Every machine in every lab falls into one of three categories. The category tells you who has to be standing there before you switch it on.
Three categories, one question
Three categories, one question
Every piece of equipment in the lab is Category 1, 2 or 3. The
category answers one question: who has to be present before you switch it on?
Permission from an instructor is required in every case. What changes between categories is
when that permission can be given, and who has to be in the room while the machine is running.
Category 1
Permission may be given in advance. Work alone once you have it.
Category 2
Permission at the time of use. A peer must be present throughout.
Category 3
Permission at the time of use. A peer and an instructor must be present throughout.
Power down safely — turn off and disconnect the equipment from its power source.
Report issues immediately — notify the instructor of any broken or malfunctioning equipment.
Return and organize — put all equipment and tools back in their designated locations.
Restore to shutdown state — return the equipment to its original, safe configuration.
Clean thoroughly — remove all dust, chips, liquids and debris from the equipment and the work area.
The habit behind the last two is 5S — the same discipline,
named and made routine.
Safety/Universal Rules
Personal Protective Equipment
What you wear, and when. Eye protection is mandatory in the lab spaces at all times; the rest depends on the task.
Personal Protective Equipment
Personal Protective Equipment
Five topics. One of them — eye protection — applies the moment you walk
in. The rest are set by what you are doing.
Eyes
Always, in the lab spaces. No exceptions.
Hearing
Prolonged exposure to loud equipment.
Feet
Closed-toe shoes, always.
Respiratory
Any grinding or sanding; hazardous dust or fumes.
Clothing & hair
Always, near anything that rotates.
Eye protection; Watch out
Eye protection
Safety glasses are MANDATORY in the lab spaces at all times.
If you wear prescription glasses
Side shields that attach to your existing frames.
Oversized safety glasses that fit over corrective glasses.
Prescription safety glasses are also acceptable.
Lens requirements
Safety glasses must be clear or yellow tinted only.
Dark or shaded safety glasses are not acceptable for indoor lab use.
Must meet ANSI Z87.1 safety standards.
Hearing protection; Watch out
Hearing protection
Industry standard: shop tools nearly always require hearing protection in
professional settings. In a teaching lab the exposure is typically shorter than in production
work, but the protection still matters.
When to use it
Required for prolonged exposure to loud equipment — grinders, sanders, planers and similar.
The rule of thumb: if you have to raise your voice to be heard by someone at arm’s
length, it is loud enough to need protection. You do not need a meter, and most shop
tools fail this test the moment they start.
The numbers behind it
OSHA measures noise as an average across the working day, in A-weighted decibels
(dBA). Two figures matter:
85 dBA
The action level, averaged over 8 hours — the point at which a workplace must run a hearing conservation programme.
90 dBA
The permissible exposure limit, averaged over 8 hours.
Above 90 dBA the allowed time drops fast — every extra 5 dBA halves it:
90 dBA
8 hours
95 dBA
4 hours
100 dBA
2 hours
105 dBA
1 hour
110 dBA
30 minutes
115 dBA
15 minutes or less
Impact noise should not exceed 140 dB peak — a single hammer blow or
nail gun can reach it, and that damage is immediate rather than cumulative.
These are OSHA workplace limits (29 CFR 1910.95). NIOSH recommends a stricter
85 dBA limit that halves the allowed time every 3 dBA rather than every 5. Hearing loss
from noise does not come back, so treat these as ceilings, not targets.
Two types available
Earplugs
Small foam plugs inserted into the ear canal. Disposable or reusable. Available on request from the instructor.
Ear muffs
Over-ear cups covering the whole ear. Reusable and adjustable. Often preferred for intermittent use.
Both types significantly reduce harmful noise levels.
Foot protection
Foot protection
Minimum requirement: closed-toe shoes are MANDATORY — no sandals, no flip-flops, no open-toe footwear.
Recommended upgrades
Slip-resistant soles, for traction on surfaces that may be slippery.
Puncture-resistant soles, against sharp metal debris.
Steel-toe or composite-toe protection — recommended, not required.
Avoid
Canvas shoes or thin-soled footwear.
High heels or unstable footwear.
Anything that does not fully enclose your feet.
You will be standing for most of the lab period — choose something
supportive and comfortable.
Respiratory protection; Stop
Respiratory protection
MANDATORY when using any grinder or sander, and when working with materials
that produce hazardous dust.
Grinding galvanized material is PROHIBITED. Zinc fumes from galvanized steel
are toxic when heated.
Health hazards
Metal dust and particles cause respiratory irritation and long-term lung damage.
Wood dust can cause allergic reactions.
Dust and fumes are not the same problem, and they do not take the
same protection. The next section is the one that decides which you need.
Respiratory protection — what to wear; Stop; Watch out
Respiratory protection — what to wear
A dust mask does nothing against fumes or vapours. An N95 is a
particle filter. It does not stop gases, welding or brazing fume, solvent vapour, or
anything else you can smell. Wearing one while you can smell the air is not protection.
For dust — grinding, sanding, sawing
N95 mask
Filters 95% of airborne particles. The minimum for dusty work.
Half- or full-face respirator
Fitted with a particulate filter, for heavy or extended dust.
For fumes and vapours
You need an approved respirator with the right chemical cartridge, not a
dust mask. Ask the instructor which cartridge before you start.
A respirator only works if it seals. A loose mask, or a beard along the
seal, defeats it.
If there is no correct cartridge available, the job does not happen until
there is.
If you can smell fumes or taste particles, your protection is inadequate.
Stop work immediately and upgrade it — or stop the job.
Loose clothing and accessories catch in rotating machinery. That is how this
causes serious injury or death — it is not a dress code.
Prohibited
Loose-fitting clothing, or garments with dangling features — drawstrings, ties and similar.
Long sleeves, hoodies or jackets near rotating equipment.
ALL jewelry, except silicone wedding rings.
Neckties, scarves and lanyards.
Hair, and what to wear instead
Hair, and what to wear instead
Hair
Long hair must be secured back and kept away from equipment.
Use hair ties, clips or caps to prevent entanglement.
Recommended
Cotton or fire-retardant materials — preferred, not required.
Close-fitting, short-sleeved shirts.
Pants without excessive loose material.
Safety/Universal Rules
Lifting and Carrying
Team lifting above 40 lbs, and the technique that keeps you in control of the load. What usually defeats a lift is the size of the thing, not its weight.
Lifting Rules; Watch out
Lifting Rules
Get a second person for anything over 40 lbs. A gym weight plate is
45 lbs and nobody lifts one in pairs. Size — not weight — is what makes shop
materials hard to carry.
Forty pounds of aluminum bar is about four inches square and two feet long: you can hold it
against your chest, see over it, and set it down where you meant to. A twenty-foot piece of tube
can weigh less than that and still put half its length out in front of you, and a sheet of
plywood fills your arms and hides the floor you are walking on. Same weight, different job.
OSHA sets no weight limit — no standard says how much a person may
lift, only that a workplace be kept free of recognized hazards. The number everyone borrows
comes from NIOSH, the federal institute that researches workplace injury:
51 lbs with two hands under ideal conditions, cut for every way a real
lift is worse. Hold that same load at arm's length instead of against you and it rates about
20 lbs. Turning a quarter circle as you lift takes off another 30%, and
nothing good to grab takes off 10% more. A load much wider than your body is outside what the equation covers
at all — used there, it underestimates the hazard.
Team lifting is required for
Anything over 40 lbs.
Items lighter than 40 lbs but awkward in shape, size or balance.
Any object that feels unstable or is difficult to grip.
The 40 lb line is as much about dropping it as about your back.
A load you cannot fully control is a hazard to your feet, the floor, the workpiece and anyone
walking past — well before it is a hazard to your spine.
If you cannot hold it against your body and keep your back straight, it is too heavy
for you to lift alone — whatever the number says. Weight still wins in the end;
that point just sits somewhere different for every person and every shape.
Proper lifting technique; Checklist
Proper lifting technique
Plan the lift — clear your path and know where you are going.
Get close to the object before lifting.
Squat down using your leg muscles; keep your back straight.
Grip firmly with both hands; avoid awkward hand positions.
Lift smoothly using your legs, not your back.
Keep the load close to your body throughout the lift.
Setting it down
Use the same technique in reverse — squat down, do not bend over.
Place objects gently. Do not drop them.
Safety/Universal Rules
Electrical Safety
Why 50 V is a workplace control threshold, why 5 V can still burn you, the inspection required before every use, cords on the floor, and what to do when someone is shocked.
Electrical Sources
Electrical Sources
What hurts you at 5 V is not what hurts you at 240 V; one is a burn hazard
while the other is a shock hazard.
5 V / 12 V
The power supply on the bench, batteries, and the battery
pack out of a cordless drill. Lower shock risk, not a magic cutoff. Not below the
burn threshold.
120 V
Wall outlets. Dangerous — can cause serious injury or
death.
240 V / 480 V
Industrial equipment. Extremely dangerous — often
fatal.
Voltage tells you whether a circuit can push current through you. It does
not tell you what that circuit can do to a ring, a dropped tool or a shorted cell.
Those are two different hazards with two different thresholds. The next two sections are
about how each hazard changes.
Electrical — Shock Hazard; Stop
Electrical — Shock Hazard
There is no magic voltage at which shock suddenly becomes possible. A shock can be
painful without being life-threatening, and its severity depends on current, path, duration, and
your body’s resistance. Higher voltage can drive more current through the body, so the risk of
serious injury rises with it. In U.S. workplace rules, 50 volts is a common
control threshold: at or above it, live parts must be guarded and work near exposed live parts
requires specific controls.
OSHA requires live parts to be de-energized before you work on or near them — and then
says that “live parts that operate at less than 50 volts to ground need not be
deenergized if there will be no increased exposure to electrical burns or to explosion due to
electric arcs” (29 CFR 1910.333(a)(1)). Read that second
half again; the rest of this page hangs on it.
At or above the line, live parts must be guarded against accidental contact.
The rule is written for “electric equipment operating at 50 volts or more”
(29 CFR 1910.303(g)(2)(i)).
That number applies to DC as well as AC. The standard does not distinguish
between them, and OSHA has stated it “considers all voltages of 50 volts or above to be
hazardous” (interpretation letter, 4 September 2015).
NFPA 70E draws the same line. Below 50 V you may work live only where the
capacity of the source and any overcurrent protection have been considered and found
not to add burn or arc exposure (2024 edition, 110.2(B) Exception No. 5).
Supporting detail: Addendum 1 — “It’s not the voltage that gets you, it’s the current”.
Supporting detail: Addendum 2 — The international standards are not one number.
In this lab, use 50 V — AC or DC. It is the number OSHA enforces,
it is the most conservative of the figures above, and it assumes nothing about your skin being
dry or your hands being clean. If a circuit is at or above 50 V, it is not something you
work on live.
Electrical — Burn Hazard; Stop
Electrical — Burn Hazard
Below 50 V, the primary concern often shifts from shock to
short-circuit current. This is the half of the page people get wrong, because the
voltage people assume is harmless is the one nobody is careful with.
Look at what the exemption above is actually conditioned on. Not shock — burns
and arcs. NFPA 70E names the same condition as the capacity of the source.
Both standards are telling you that once you are under that workplace control threshold, the
question changes from how many volts to how many amps can this thing deliver into
a dead short.
Where the current comes from
A bench supply set to 5 V will deliver its full rated current into a
short without complaint. That is what the current limit is for — and if you have wound the
limit up to get a motor turning, you have wound the protection off.
A lithium cell or pack has almost no internal resistance. Shorted, a single
cell can dump tens of amps within milliseconds. A pack does considerably worse.
A lead-acid battery is rated in hundreds of cold-cranking amps — and
that is a 30-second load test, not a ceiling. A dead short pulls far more.
None of these can push meaningful current through your body at 12 V. All of them can push
hundreds of amps through a piece of metal — and metal carrying current it was never sized
for gets hot, fast.
Metal jewelry is the classic way this happens
ALL jewelry is already PROHIBITED here — see
clothing and jewelry. That rule was written for rotating machinery. It earns its keep a
second time on the bench, and OSHA writes it a second time for exactly this reason: conductive
jewelry “may not be worn if they might contact exposed energized parts”
(29 CFR 1910.333(c)(8)) — a rule that states no voltage
floor. The same sentence gives the way out: such articles may be worn if they are
“rendered nonconductive by covering, wrapping, or other insulating means.”
A ring or a metal watch band bridging a low-voltage source is a near-zero-resistance path
across something that can supply hundreds of amps. The ring becomes the heating element. This is
documented injury, not a story: a mechanic’s gold ring touched the positive terminal of a
12 V car battery while the wrench in his hand bridged the ring and the
negative terminal, and the result was a deep circumferential burn around the base of the finger
that needed a skin graft. A review of nine ring burns at one burn center found the same pattern:
the small size of the burn hides how bad it is, because a burn that wraps a
finger is far more likely to need grafting and to leave lasting loss of function than a burn of
the same area anywhere else.
You can drop a wrench. You cannot drop a ring.
The silicone wedding ring that the PPE rule allows is also the right answer
electrically: silicone does not conduct, so it cannot become the short.
A shorted lithium cell does not just get warm
An external short is one of the recognized triggers for thermal runaway
— the cell generates heat faster than it can shed it, and the outcome is
“extremely high temperatures, violent cell venting, smoke and fire” (UL Research
Institutes). Once it has started, disconnecting it does not stop it. The cell is
now its own energy source.
NEVER leave loose cells or packs where metal can bridge the terminals
— a drawer with tools in it, a pocket with keys in it, a bin with offcuts in it. Federal
transport rules require lithium cells and batteries to be packed so their terminals cannot short
(49 CFR 173.185). The reason that rule exists is the reason to do the same
thing on your own bench.
A cell that has been shorted, dropped, crushed, punctured or has swollen is out of
service. Tell the instructor. Do not put it back on charge to find out. See
Fire Safety.
The sentence to take away: low voltage does not mean low energy.
Voltage helps determine whether a circuit can shock you. Current decides whether it can burn
you — and current is set by what the source can deliver and what is in the path,
not by the number printed on the front of the supply.
Electrical Conductors; Stop; Watch out; Checklist
Electrical Conductors
Inspect every cord, every time, before it goes into the receptacle.
Never run your hand along a cord while it is plugged in; that is a dangerous way to find fraying.
It takes about five seconds, and it is the one check that catches most of this page before it
happens rather than after.
With the cord unplugged, run it through your hand end to end. Look for frayed,
cracked, cut or exposed insulation, and for flat spots where something has been driven
over it.
Check the plug: blades all present, straight, tight in the body, not
discolored or pitted. Check the ground pin is still there — a missing
ground pin means the cord is out of service, not that you have found a workaround.
Check where the cord enters the plug and enters the tool. That is where
flexing breaks conductors, and it is where the damage hides.
Inspect extension cords for cuts, crushing and wear, and check the receptacle end for
scorching or melted plastic.
Damage like this means the cord is finished, not that it needs watching.
If you find damage, stop, unplug it, and notify the instructor. Not
“just for this one cut”. Tag it or hand it over, so the next person does not find it
the hard way.
Tape is not a repair. OSHA allows electrical tape over superficial scuffs in
the outer jacket, and has stated just as plainly that “tape repairs of the jacket may not
be used to bring a worn or frayed flexible cord into compliance” (interpretation letter,
16 December 1998). If conductors or their insulation are showing, the cord is done.
Connections and plugs
Always disconnect power before performing any maintenance or adjustment.
NEVER yank or pull a cord — grasp the plug, not the cord. Pulling by
the cord wrecks the strain relief where you cannot see it, and it is how a plug ends up
half out of the receptacle with the blades exposed.
Push a plug fully home, and look at it. A plug that will not seat is a
fault to report, not a fit problem to force.
Keep electrical connections away from water and wet surfaces. Wet skin has on the order of
1,000 ohms of resistance where dry skin has 100,000 ohms or
more, so water moves you roughly a hundredfold closer to the current every rule on this
page is trying to keep out of you.
Be aware of overhead wiring when you are handling long stock, moving a
ladder or lifting.
A partly unplugged appliance is a short waiting for something to land on it
The hazard is the gap, and it is there before anything lands in it.
Exposed blades sit at full line voltage with nothing between them but air. Anything
conductive that falls across them completes the circuit straight across the supply — and
in a shop, the thing that falls is a metal chip. What follows is not a shock.
It is a dead short: a bang, a hard flash, and enough heat at the contact point to weld and
pit the blades. It will very likely trip the breaker and it can wreck the outlet or whatever
is plugged into it. The breaker protects the wiring, not your face, and it does not act until
after the flash.
Plugs are all the way in or all the way out. Nothing in between, and nothing
left in between.
Chips travel further than you expect and they conduct — see
Metal Chips and Swarf. That is the direct line between the housekeeping rules and this one.
Cords on the floor — the one most likely to get you; Stop; Checklist
Cords on the floor — the one most likely to get you
Nothing else on this page is as likely to actually injure someone as a cord
lying across a walkway. It is not a shock hazard at all. It is a trip hazard
— and a trip in a shop is not a trip onto carpet. You land on concrete, or into a machine, or on something sharp.
The regulation treats this as a floor problem rather than an electrical one:
“walking-working surfaces are maintained free of hazards such as sharp or protruding
objects, loose boards, corrosion, leaks, spills, snow, and ice”
(29 CFR 1910.22(a)(3)), and passageways and work areas are kept “in a
clean, orderly, and sanitary condition” (29 CFR 1910.22(a)(1)). A cord
across an aisle is an obstruction in an aisle.
A trip in a shop is not a trip onto carpet. You land where the machines are.The correct route is longer and costs nothing. That is the whole argument.
What to do, in order of preference
Do not cross the walkway. Move the work to the outlet, or use a different
outlet. This is almost always available, and it is almost never the first thing anyone tries.
Route along the wall or the bench line rather than across open floor. Take
the long way around the edge of the room.
Go overhead where a drop or a reel is provided. That is what they are
for.
If it genuinely must cross, cover or anchor it. OSHA’s own guidance is
to “ensure that temporary electrical cords that cross aisles are taped or anchored to the
floor”. A cord ramp or cord cover does the same job better and protects the cord as well
as the person.
Use the shortest cord that reaches. Slack on the floor is the hazard, and a
coiled surplus in a walkway is the same hazard in a tighter package.
Unplug it and put it away when you are done, in the same movement as
shutting the tool down. The cord left out after the job is finished is the one nobody is
expecting.
PROHIBITED — running a flexible cord through a doorway, a window, or a hole in
a wall, ceiling or floor, and attaching it to building surfaces. Those are named
prohibitions in the electrical standard (29 CFR 1910.305(g)(1)(iv)),
along with using flexible cord as a substitute for the fixed wiring of a building. Flexible cord
is temporary by definition. A cord treated as permanent gets pinched, crushed and forgotten.
NEVER walk past a cord lying across a walkway and leave it because it is not
yours. If you can see it, you can move it or say something. The person who trips over it will
not have seen it.
Read from the cord’s side, the rule is the same: portable equipment must be
handled so it is not damaged, and every cord set must be inspected before use on any shift for
cuts, crushing and a pinched jacket (29 CFR 1910.334(a)). A cord that gets
walked on is a cord that fails the inspection above. This section and that one are the same
problem twice.
Keeping walkways clear is the Set in Order and Shine part of
5S. The safety case and the lean case are the same case.
If someone is shocked; Stop; Watch out
If someone is shocked
Do NOT touch them directly. If current is still flowing they are part of the
circuit, and grabbing them puts you in it as well.
Kill the power first — the machine switch, the disconnect, the
breaker, or pull the plug.
If you cannot kill it, use a dry, non-conductive object to separate them
from the source, and stand on something dry while you do it.
A small mark is not evidence of a small injury. Electrical and electrothermal
burns run deep with very little to see on the surface, and a burn that wraps a finger can cost
the use of it. Any shock, and any electrical burn, gets reported and gets looked at
— however fine the person says they are.
Safety/Universal Rules
Chemicals and Safety Data Sheets
Every chemical and liquid in the shop has a Safety Data Sheet. Read it before you use the material, not after.
What is a Safety Data Sheet (SDS)?
What is a Safety Data Sheet (SDS)?
A Safety Data Sheet is the manufacturer's written answer to
what their product can do to you, what to wear, and what to do when it goes wrong.
There are sixteen sections, always in the same order. You do not need to read a SDS front to
back but you should read the following three sections before you use a product.
Section 2
Hazard(s) identification. What the chemical can do
to you, in the manufacturer's own words — a signal word, the hazard statements, the
red-bordered pictograms.
Section 4
First-aid measures. On skin, in eyes, breathed in,
swallowed.
Section 8
Exposure controls / personal protection. Gloves,
eye protection, ventilation — the PPE answer for that specific chemical, rather
than the general one.
None of this is a local rule. OSHA requires a sheet for every hazardous chemical, and requires
the sixteen sections and the order they come in — 29 CFR 1910.1200(g).
Supporting detail: Addendum 3 — All sixteen sections, and the four OSHA does not enforce.
Supporting detail: Addendum 4 — Signal words, pictograms and H-numbers — how Section 2 is written.
Where is SDS binder located?
Where is SDS binder located?
All Safety Data Sheets are organized in a designated binder for easy reference.
Review before use — check the sheet for any unfamiliar chemical or liquid.
Ask the instructor if you cannot locate the sheet for a material.
The binder is one way of satisfying the rule underneath it.
1910.1200(g)(8) requires an employer to keep the sheets "readily accessible
during each work shift to employees when they are in their work area(s)", and allows
electronic copies in place of paper "as long as no barriers to immediate employee access in
each workplace are created by such options." Binder or screen, the test is the same: the
sheet is something you can reach now, not something you have to go and ask for.
Your responsibility: know the hazards of any chemical you are using, and
follow the proper handling procedures.
Supporting detail: Addendum 5 — Telling a current sheet from an old one.
Material Storage and incompatible materials
Material Storage and incompatible materials
Flammable liquids must be stored in an approved flammables cabinet when not in use.
NEVER store incompatible chemicals together.
All containers must be properly labeled.
“Incompatible” is not a judgement call, and answering it needs no
chemistry. It is written on the sheet, by name, in two places:
Section 10
Stability and reactivity. One of its required
entries is "incompatible materials" — what this chemical must not contact.
Beside it sit "conditions to avoid" and "hazardous decomposition products",
which is what the two of them would make.
Section 7
Handling and storage. Required to give
"conditions for safe storage, including any incompatibilities" — the same
question answered for the shelf rather than for the reaction.
So the test before two things share a cabinet: open both sheets and read Section 10 on
each. The entry may name a specific substance or a whole class of them — oxidizers,
strong acids. If either sheet names the other material, they do not go together. Read both,
because the pair may only be called out on one of them.
Supporting detail: Addendum 6 — What makes a flammables cabinet “approved”, and how to spot one.
Safety/Universal Rules
Machine Hazards and Housekeeping
The two ways a machine injures you - it catches hold and pulls you in, or it closes on you - plus the environment around it and the habits that keep both off you.
Rotating machinery; Stop; Watch out
Rotating machinery
Rotating machinery injures you by catching hold of something and pulling
it in. It does not have to catch your hand. It catches a sleeve, a glove, a lanyard or a
strand of hair, and your hand goes wherever that goes.
Gears, pulleys and belts, chains and sprockets are extremely dangerous.
Where a rotating part meets another surface there is a wedge that closes to nothing — an
in-running nip point, the place the machine feeds things into itself. It is
where the belt runs onto the pulley, where the chain runs onto the sprocket, where the gear
teeth mesh.
The contact and the injury happen in different places. You touch the belt out
in the open, where it looks like a moving strap; the belt carries you to the pulley, where there
is no gap at all. That distance is why staying clear of the nip point is not enough on its own
— anything the machine can grip is a handle it uses to bring you there.
Gloves. Gloves or rags are for handling sharp objects such as cutters, and
only once the machine is shut down. NEVER wear gloves at a running
machine — a glove catches where bare skin would pull free, and takes your hand
with it. See chips and gloves.
It does not take teeth, and it does not take speed. A plain smooth shaft turning
slowly will still wind hair or cloth onto itself, and once it has a turn or two it does not let
go.
Contact happens where the belt is open. The injury happens where it closes.
Supporting detail: Addendum 7 — The word for this, and where it comes from.
The rotating parts that have no cover
Belts, gears and chains belong behind covers. The working end of a machine does
not. The spindle — the driven shaft the motor turns — the
chuck that grips the tool or the work, and the stock (the raw
material) held in it all turn out in the open. Nothing is between you and them, because you have to
reach them to do the job.
So everything above about what gets caught applies here with nothing in the way — and it
applies to every machine that turns, not only the loud ones. A drill press is
quiet, it is slow, and it looks like the harmless one. It is still an open chuck spinning, and it
will wind hair, a sleeve or a glove onto itself like anything else. Slow is how long it
takes, not whether it happens.
The sleeve tore before the arm did. That is the shirt’s doing, not the machine’s.
The lathe is where this goes furthest, and the reason is what a lathe is. Most
machines hold the work still and move a cutter across it; a lathe does the opposite and
turns the work. What is spinning in the open is then not a bit the width of a
pencil — it is the whole part, as long and as heavy as that part happens to be. That is why
the fatality reports for lathes describe something other than a hand injury: a person wound onto
their own workpiece.
Wound on, cloth is a rope. Each revolution takes up another turn, and bracing changes nothing.
The question, before anything is switched on: what is turning, and what of mine can
reach it? A sleeve, a glove, loose hair and a strip of abrasive cloth held against the
work have each pulled somebody into a machine. Every one of them is easier to deal with before
the spindle is turning than after.
None of this is a ranking. The mechanism is the same on every machine that turns,
and the one that can catch you is whichever one you are standing at.
Supporting detail: Addendum 8 — What the investigations actually describe.
Moving machinery and pinch points; Watch out
Moving machinery and pinch points
Moving machinery injures you without ever catching hold of you.
Two surfaces close on each other with you in between. Nothing pulls you anywhere — you run
out of room.
What makes a pinch point
A pinch point is a gap that is closing: two parts, at least one of them
moving, with space between them that is on its way to nothing. That is the whole of it, and it is
why pinch points are hard to spot. There are no teeth, no edge and often no noise. A wide gap and
a narrow gap look the same until the last inch, and the gap does not care what is in it.
Two kinds of movement, and both make one:
Back and forth, up and down
A press ram, a drill head coming down, a saw guide
being lowered, a clamp closing. You are caught between the part that moves and the part that
does not.
Straight along
A table, a carriage or a saddle travelling. It closes the gap
against whatever waits at the end of its travel — a stop, a column, the machine’s
own frame, or the hand resting there.
Where they hide
Between the work and whatever holds it. A vise jaw, a clamp, a fixture: the
hand steadying the workpiece is inside the gap that is closing on the workpiece.
At the end of a table’s travel. Wind it far enough and the space
between the table and the frame goes to zero, with whatever was resting there in between.
Under anything that comes down. A head, a ram, a guard, a guide.
On hinges. Covers, doors and lids close on their own frames — at the
free edge, where a hand is holding them, and again right at the hinge, where the gap closes over
almost no distance at all.
A pinch point needs no power, no speed and no noise. A vise turned by hand
multiplies what you put into the handle many times over, and it closes slowly and quietly enough
that nothing warns you. Switching a machine off removes the part that would have closed the gap
for you. It does not remove the gap.
The question to ask
Before moving anything — a handwheel, a lever, a clamp, a guard —
what closes, and what is in the way? Follow the moving part to the end of its
travel and find what it meets there. Then look at where your hands are, and where they will still
be once you are watching the cut instead of watching your hands.
A pinch point is a gap on its way to zero. It looks safe for most of the trip.
Supporting detail: Addendum 9 — Why belts and chains count as rotating, not pinching.
Guards stay on, and taking one off is not your call; Stop
Guards stay on, and taking one off is not your call
A guard is the thing standing between you and everything the two sections above
describe. It is not an accessory, and it is not in your way — it is doing the one job
nothing else on the machine does.
No one removes a guard in this lab. A machine that needs a guard off is the
instructor’s to deal with, out of class.
That is the whole rule, and it is deliberately not a judgement call. You do not have to decide
whether this particular setup is the exception, whether the cut is short enough, or whether you
will be careful. If the guard is in the way, the answer is to stop and say so — not to
work out whether you can manage without it.
It also means a machine you find with a guard already missing is not ready to use.
Say something. You have not done anything wrong by finding it that way, and the person who uses it
after you has no way of knowing.
Supporting detail: Addendum 10 — Why the rule has no exceptions in it.
Lockout/Tagout — before anyone works on a machine; Stop
Lockout/Tagout — before anyone works on a machine
Everything on a machine that turns or travels does so because something is
powering it. Lockout/Tagout is how that power is taken away and kept away while somebody
works on the machine.
NEVER work on equipment with rotating or moving parts without first
disconnecting power.
Lockout/Tagout procedures must be followed for maintenance.
The two words
Lockout
A lock on the device that isolates the energy — the disconnect,
the breaker, the valve — so it physically cannot be switched back on.
Tagout
A tag on that same device saying who put it there and why, so nobody
removes it wondering.
Off is not disconnected, and disconnected is not still
Off is not disconnected. A machine’s own on/off switch is a control.
Someone can press it back on, and either way the machine is still connected to its supply. The
disconnect is the thing that gets locked.
Disconnected is not still. A spindle coasts. A raised head or ram drops. A
spring, a charged capacitor or air still in a line will all move something after the power is
gone. Energy already inside the machine is part of what the procedure has to deal with.
Supporting detail: Addendum 11 — What the standard actually covers.
The environment around the machine
The environment around the machine
Slip hazards
Clean dust, metal chips, water and coolant off the floor immediately.
Lighting
Ensure lighting is adequate before operating any machine.
Walkways
Keep aisles and emergency exits unobstructed.
Operating habits
Operating habits
The chuck key never leaves your hand. It is not released until it is out of
the chuck. There is no moment where the key is in the chuck and not in your grip — not to
reach for something, not to answer someone, not for a second.
Stop machines completely before taking measurements or making adjustments.
Secure all workpieces before operation — use clamps, vises or fixtures.
Never leave tools on or near operating machinery.
Supporting detail: Addendum 12 — Why the chuck key rule is worded as a grip and not as a reminder.
When to fight a fire and when to leave, and how to use an extinguisher.
Decide before you reach for anything; Stop; Checklist
Decide before you reach for anything
An extinguisher is for a small fire you caught early.
Fight it only if all four are true
The fire is small and contained — a bin, a rag, a puddle. Not spreading.
You know what is burning, and you have the right extinguisher for it.
You have a clear exit behind you and the fire is not between you and it.
Someone else has already raised the alarm.
Otherwise: get out. Pull the alarm, leave, call 911 from
outside, and tell the instructor and the fire crew what was burning.
If you try and it does not go out in the first few seconds, stop and leave.
A hand extinguisher lasts roughly 10–20 seconds. That is your whole attempt.
Using an extinguisher — PASS
Using an extinguisher — PASS
Remember the acronym: P–A–S–S.
When it looks out, back away watching the fire, exit behind
you. Do not assume it is over — a knocked-down fire can reignite.
Fire classes, and what puts them out
Fire classes, and what puts them out
Fires are classed by what is burning. An extinguisher is rated
for the classes it can handle, and using the wrong one ranges from useless to dangerous.
Most extinguishers on a wall are ABC dry chemical — one
unit covering the first three classes. Check the label; the classes it is rated for are printed
on it.
Metal fires, and what it takes to start one; Stop; Watch out
Metal fires, and what it takes to start one
Metal burns only when it is divided finely enough, and then only when several
conditions line up at once. Ordinary aluminum chips and swarf will not do this,
and neither will the quantities of fine material a lab space like this one generates. Solid stock
does not burn at all. The cases below are the ones that are genuinely different.
The form matters more than the metal
Magnesium is the real Class D case. Thin sections, chips and turnings
ignite readily and burn with intense heat and a brilliant white light, and dull tools alone can
produce enough heat during machining to start it.
Titanium turnings can ignite, and titanium fines and grinding dust are
worse — fine enough that a static discharge is a credible ignition source.
Aluminum fines — the dust off sanding, grinding, buffing and
polishing — are a genuine hazard, but only through the specific mechanisms below.
Aluminum chips and swarf are hard to ignite. Aluminum carries heat away
from a hot spot fast, it wears a tough oxide skin that holds together while the metal
underneath melts, and a chip has little surface area for its mass. Put a torch to a pile of
chips and they melt.
Solid stock does not burn. A block of aluminum is not fuel.
Magnesium and titanium are not common in student labs. A senior project
might bring one in. If you are about to cut, grind or sand either one, ask
first — every time.
Size is the usual line — shape is the exception
The line in the standard is about half a millimeter, measured across a
particle’s smallest dimension — which different editions write as
500 microns or as 420 microns (fine enough to pass a 40-mesh sieve), not two separate
limits. Below it, metal dust can carry an explosion. Above it, generally it cannot — and
generally is the word the standard uses, not never.
Flakes are the exception, and buffing and polishing make flakes. A flake is
wide but thin, so it is too big for the sieve and still burns like dust. Treat anything off a
buffing or polishing wheel as fines however big it looks. Machining chips are genuinely coarse
— that is the difference between a chip tray and a dust collector.
The ways fine metal actually ignites
A suspended dust cloud meeting an ignition source. Fines sitting in a tray
are not the hazard. Fines thrown into the air, at the right concentration, reaching a flame, a
torch, a spark or a static discharge, are — burning travels from one particle to the next
with extreme speed. It is why you never blow fine dust around, and why you do not raise a cloud
of it cleaning up.
Fines heavily mixed with rust or grinding scale. Aluminum plus iron
oxide — rust, or the scale off steel grinding — is a thermite reaction: the
aluminum strips the oxygen off the iron, so the mixture burns without needing air from outside.
That is what makes it a metal fire rather than an ordinary one, and why water and an ABC
extinguisher do nothing to it. It takes a real mixture to go — something near
three parts iron oxide to one part aluminum by weight, and an ignition source
far hotter than a spark. That is a rust-caked pile, not a trace. See Metal Chips and Swarf for how far
apart that threshold and the recycling one actually sit.
Wet fines. Aluminum fines in contact with water slowly give off hydrogen.
That is a reason not to seal damp fines into a closed container, and part of the reason water is
the wrong thing to put on a metal fire.
If fine metal does ignite
Do not fight it. Most general-purpose shops have no Class D
extinguisher — assume you do not have one unless somebody has shown you
where it is. Pull the alarm, get out, call 911, and tell the fire crew
it is a metal fire. That changes how they fight it, and they need to know
before they arrive with a hose.
PROHIBITED — the ABC extinguisher off the wall. “Dry
powder” (Class D) and “dry chemical” (ABC) are not the same thing. An ABC
unit throws an incompatible agent at pressure: it scatters burning fines and spreads the
fire.
NEVER put water on a metal fire. The stream throws burning material, can
raise an explosive dust cloud, and reacts with the metal to release hydrogen.
Alarm, evacuate, report.
Supporting detail: Addendum 13 — Why dry sand is on the list, and why it is probably not on yours.
What that means day to day
Do not let fine dust accumulate. Empty trays, vacuums and collectors rather than letting
them fill — see Machine Hazards and Housekeeping for housekeeping.
Chips and fines are disposed of differently, and the difference matters — see
Metal Chips and Swarf.
Let hot chips and debris cool before they go anywhere near a bin of paper or rag.
Ask before you machine an unfamiliar metal. If you do not know what it is,
that is the answer: ask.
Hot work and the things that start fires
Hot work and the things that start fires
Grinding throws sparks a surprising distance. Clear rag, sawdust, solvent
and packaging out of the area before you start, not after it smolders.
Oily rags — it depends entirely on which oil.Drying oils — linseed, tung, oil-based stains, varnishes and finishes
— cure by reacting with oxygen, and that reaction gives off heat. Bunched in a pile the
rags hold the heat in, and the pile can reach ignition on its own with nothing to light it.
Those rags NEVER go in a pile: spread them flat to dry, drop them in water, or
use the designated container.
Petroleum oils do not do that. Way oil, cutting fluid, hydraulic oil and
ordinary shop oil do not cure by oxidation, so a rag wiped with them will not self-heat and will
not spontaneously combust. It is still combustible — a spark or a hot
chip will light it like any oily cloth — so keep it away from hot work and out of a bin of
paper or sawdust. If you do not know which oil is on the rag, treat it as a drying
oil.
Chips come off hot, razor sharp and fast. How to handle them, how to clean them up, and the rules on compressed air.
Four reasons a chip is dangerous
Four reasons a chip is dangerous
A chip is not scrap until it has cooled and stopped moving. Straight off the
tool it is every one of these at once.
Hot
Where an aluminum chip forms, the cut runs roughly
250–650 °C (500–1200 °F), depending on the alloy
and the speed. Chips do not look it.
Sharp
The leading edge of a chip is always razor sharp. It is
a freshly cut edge and it will open a hand.
Strong
A long continuous chip is a steel ribbon. If it wraps a sleeve or a
limb it can pull you into the machine.
Slippery
Chips on the floor roll underfoot. This is one of the most common
ways people get hurt without the machine touching them.
Never clear chips with your hands; Stop
Never clear chips with your hands
Do not reach into a machine to clear chips while it is running, and do not
pick up a long stringy chip by hand at any time. Stop the spindle, then deal with it.
Gloves
Gloves may only be used for cleanup after the machine is shut
down.
Never wear gloves at a running machine. A glove catches where bare skin
would pull free, and takes your hand with it — see Machine Hazards and Housekeeping.
Brush
A brush may be used while the machine is in operation — your hands stay
outside the machine. If clearing the chip means reaching in, stop the spindle first.
On a CNC machine, take particular care: the tool can move without warning, and the
enclosure invites you to reach further in than you should.
Compressed air — there are limits on this; Watch out; Checklist
Compressed air — there are limits on this
Compressed air is convenient and it is the option people reach for first. It is also
regulated, because a chip in a moving air stream is a projectile and air
forced against skin can be driven into the body.
The rule
OSHA permits compressed air for cleaning only where it is
reduced to less than 30 psi, and only then with
effective chip guarding and personal protective equipment
(29 CFR 1910.242(b)). All three conditions, together — not the
pressure alone.
Chip guarding is anything that stops a chip reaching eyes or unbroken skin: a
protective cone nozzle covers the operator, and a screen or barrier is what covers everyone
else.
In practice
The 30 psi is measured at the nozzle, dead-ended — blocked by the
work or a hand — and is met by a limited air nozzle or a regulator, not by the supply
pressure upstream of it.
Eye protection, every time. Everyone nearby too — you do not get to decide the
range.
Never at skin, yours or anyone else’s.
Never toward another person, and check who is behind the machine first.
Never into an enclosed space.
If air would just relocate the mess into the air or across the shop, use a brush or the
vacuum instead.
Cleaning up; Stop; Checklist
Cleaning up
Use cleaning equipment or gloves to handle chips for disposal — the sharp edge does
not dull because the machine stopped.
Clear the machine so only the residue in the bottom tray remains.
Sweep the floor, and mop if the floor is wet with coolant.
If cleaning equipment such as a vacuum gets wet, open it up and let it dry
before it is put away.
Chips and fines do not go in the same place
Chips and swarf go in the recycling container. That container is for
chips only.
Fines go in the trash. Dust from sanding, grinding, buffing and polishing,
and what comes out of a dust collector — never the recycling container.
Why — two reasons, and the second one is the safety reason
The recycler pays for clean aluminum. A clean load gets the aluminum price;
mix another metal in and the whole load drops to a much cheaper one. Fines pick iron up —
off a shared belt or wheel, off steel work at the next bench — so fines do not go in.
Compare how often each container actually leaves the building. A chip
recycling container fills slowly and can stand most of a semester between pickups; the trash
goes out daily. Fines belong in the stream that leaves, not the one that stands in the corner
for months quietly collecting more of them. Anything whose problem is accumulation does
not go in the container designed to accumulate.
Two thresholds, same observation. “There is iron in the
fines” is a real problem for the recycling price and not a fire problem — and the
reason both are true at once is that the two thresholds are orders of magnitude apart. The price
threshold is a trace: a few steel chips are enough to drop the whole load to the
cheaper price. A thermite reaction needs iron oxide — rust or grinding
scale, not bright steel — at something near
three parts oxide to one part aluminum by weight, plus an ignition source far
hotter than a spark. That is most of the pile, not a trace. Most rules in a shop have a number
behind them; knowing which number you are being measured against, and how far you
actually are from it, is the difference between following a rule and understanding it.
Fine dust burns; chips do not. Aluminum chips and swarf are hard to ignite.
The fire hazard is fines — and then only when a cloud of them is thrown
into the air and meets an ignition source, or when a great deal of rust or steel grinding scale
is mixed into them. Do not let fine dust accumulate, and do not raise a cloud of it
cleaning up.
If fine metal debris does ignite, do not fight it. The ABC extinguisher on
the wall is the wrong tool and will scatter it. Alarm, evacuate, and tell the fire crew it is a
metal fire. See Fire Safety.
Safety/Universal Rules
Lab Conduct and Emergencies
What is never acceptable in a lab, what alertness actually requires, and what to do when something goes wrong.
Prohibited behavior; Stop
Prohibited behavior
NEVER operate equipment under the influence of drugs, alcohol, or medication that causes drowsiness.
NO horseplay, pranks or roughhousing in any lab area.
Do not distract others who are operating equipment.
No unauthorized experiments or modifications to equipment.
Staying alert
Staying alert
Stay focused — maintain concentration while operating equipment.
Take breaks when tired or distracted.
Ask questions if you are unsure about any procedure.
Report unsafe conditions immediately to the instructor.
Emergency procedures; Checklist
Emergency procedures
Know the location of emergency stops, fire extinguishers, first aid kits and exits.
Call 911 for serious injuries or fires.
Notify the instructor immediately of any incident, injury, or near-miss.
Do not move a seriously injured person unless they are in immediate danger.
For electrical shock specifically, the first action is different — see
If someone is shocked.
Workspace responsibility
Workspace responsibility
Clean as you go — do not wait until the end.
Report equipment problems before they become safety hazards.
Lab Conduct and Emergencies
Lean and Quality/Lean and Organization
5S Workplace Organization
The five-step workplace organization method. It is a lean manufacturing practice, and it is also why a tidy shop is a safer one.
Why 5S sits in a safety module
Why 5S sits in a safety module
5S is a lean manufacturing method for organizing a workplace. It
earns its place here because most of what it asks for is also what keeps people from getting hurt.
A cluttered bench hides a hazard. An unlabeled container is an unknown chemical. A floor with
chips on it is a slip. Every one of those is a 5S failure before it is an incident — which is
why the shutdown steps in After operating any equipment are 5S in
everything but name.
This page is the basics. 5S will get its own expanded treatment later.
Sort — Seiri
Sort — Seiri
Separate necessary items from unnecessary ones.
Remove or relocate items that do not belong in the work area.
Keep only what you need for the task in front of you.
Set in Order — Seiton
Set in Order — Seiton
Organize and label the remaining items clearly, for easy identification.
A place for everything, and everything in its place.
Create logical, efficient storage systems.
Shine — Seiso
Shine — Seiso
Clean work areas to maintain high hygiene standards.
Reduce accident risk through cleanliness and organization.
Inspect while cleaning — that is how problems get found early.
Before starting: check the blade, guide and feed path; Checklist
Before starting: check the blade, guide and feed path
Confirm that the blade suits the material and cut. With the machine stopped and isolated for setup, expose only the blade height needed for the cut, following the installed saw's instructions.
Check the blade guard and the saw's anti-kickback equipment. A missing or malfunctioning device means the setup is not ready. No one removes a guard in this lab. A machine that needs a guard off is the instructor's to deal with, out of class (see Machine Hazards and Housekeeping).
Choose the guide for the cut: the rip fence for ripping, or the approved crosscut setup. In our labs, do not use the sled with the rip fence.
Plan support for the board throughout the cut and place the push stick within reach before starting. Check where both hands will go as the trailing end approaches the blade.
Control blade contact and kickback throughout the cut
Control blade contact and kickback throughout the cut
Kickback is material thrown back toward the feed side by the blade. Binding between the blade and fence is one cause. Do not make a cut that traps a loose cutoff there.
Use the approved guide to keep the board aligned; do not steer it freehand.
For a rip cut, push the part between the fence and blade. Use the push stick to keep hands out of the blade path, including at the end of the cut.
Feed steadily at a rate the blade can cut. Ease the feed through harder areas; do not force a struggling cut.
Keep clear of the blade while it coasts. Stop it completely before removing scraps or reaching for a finished piece near it.
Supporting detail: Addendum 14 — Why one feed rate does not fit every cut.
If material binds or kicks back: stop and report it
If material binds or kicks back: stop and report it
Do not reach after a thrown piece or try to free material beside a moving blade. Stop the saw from a safe position and notify the instructor. Have the setup checked before restarting; clearing a jam follows the isolation procedure in Machine Hazards and Housekeeping.
Support the work, keep the exposed blade short and feed without twisting or pinching the band.
Category 3 in both labs; vertical and horizontal setups differ
Category 3 in both labs; vertical and horizontal setups differ
A band saw cuts with a continuous toothed band. A vertical saw can follow a wood outline; a horizontal saw lowers its blade through clamped material. See How Saws Cut Wood and Choosing a Woodworking Machine.
Before starting: match the blade and stabilize the work; Checklist
Before starting: match the blade and stabilize the work
Confirm that the installed blade suits the material, thickness and intended curve. Teeth per inch (TPI) alone do not establish suitability.
Check that wheel covers are closed. On the vertical saw, in our labs, set the upper blade guard approximately 1/4 inch above the work, with the machine off.
In our labs, use stock with a flat supporting surface. On the vertical saw it rests flat on the table; on the horizontal saw it seats against the vise's fixed surface and is firmly clamped.
Plan forward exits from the cut and hand positions that stay out of the blade path. Avoid a layout that requires twisting the band or repeatedly backing out.
Feed steadily; do not force a curve or withdraw against a moving band
Feed steadily; do not force a curve or withdraw against a moving band
Vertical saw: hold the work flat against the table and feed at a moderate, steady rate the blade can cut. Keep hands away from the line of cut. Do not twist the blade to force a tighter turn. In our labs, stop the machine before backing out of a long cut; wait until the band has stopped.
Horizontal saw: keep the work clamped. Where the saw has a hydraulic feed control, use the trained adjustment procedure to set a controlled descent for the material and section. Do not apply the vertical saw's hand-feeding method to this setup.
Supporting detail: Addendum 15 — Why thickness matters as well as material.
If the blade breaks or pinches: stand clear and stop
If the blade breaks or pinches: stand clear and stop
If the band breaks, step clear and use the emergency stop if safely reachable. Do not open wheel covers or try to catch the band. If the blade pinches, stop and get the instructor before freeing the work under the isolation procedure in Machine Hazards and Housekeeping.
Support the board against the fence, keep clear of the full blade path and use the cutting motion taught for the installed saw.
Crosscuts and angled ends: Category 3 in the woods lab
Crosscuts and angled ends: Category 3 in the woods lab
A miter saw cuts a board to length or cuts an angled end. The miter setting turns the cut across the table; the bevel setting tilts the blade. See How Saws Cut Wood and Choosing a Woodworking Machine.
Before starting: set angles, support the board and check clearance; Checklist
Before starting: set angles, support the board and check clearance
With the machine off and isolated for setup, set and secure the miter and bevel angles. Mark the cut and check its alignment with the stationary blade's path; a laser, if fitted, is an alignment aid.
Seat the board against the fence and table. Support long ends at the same height as the saw table so the board cannot tip during the cut.
Check that the moving guard works and shields the blade. If a dust collector is fitted, check that it is ready for use.
Check the entire blade path at the selected angles, including clearance from clamps. In our labs, keep all body parts at least 6 inches from the blade and never cut small pieces. If the piece cannot be supported while maintaining that clearance, stop and ask for another method.
Keep the work still and use the motion taught for this saw
Keep the work still and use the motion taught for this saw
Secure the work against the fence using the trained holding or clamping method. Do not improvise a stacked-board cut; have the instructor establish the setup.
With hands outside the blade path and the blade clear of the work, start the saw and let it reach cutting speed.
Make the cut with controlled feed using the motion demonstrated for the installed saw. A sliding saw needs its own cutting sequence. Have that demonstrated before using the slide; do not interpret “pull through” as permission to pull a spinning blade toward you through the board.
At the end of the cut, release the trigger, keep the head controlled and wait for the blade to stop before lifting it or removing the work and cutoff.
Use a blade and material combination approved for the installed saw. Changing the blade alone does not make a woodworking miter saw suitable for metal, masonry or wet cutting.
If the board shifts or the blade binds: release the trigger
If the board shifts or the blade binds: release the trigger
Keep clear of the blade and let it stop. Do not reach in to reposition the work or free a cutoff while it moves. Notify the instructor and follow the isolation procedure before clearing a jam.
Use push blocks, suitable stock and shallow cuts to keep hands clear of the cutterhead while establishing a flat face or straight edge.
Flat faces and straight edges: Category 3 in the woods lab
Flat faces and straight edges: Category 3 in the woods lab
A jointer establishes a flat face or a straight edge at a set angle to an adjacent face. It does not by itself make opposite faces parallel. See Milling Rough Lumber Square for the sequence and Choosing a Woodworking Machine for machine selection.
Before starting: check the stock, guard and depth of cut; Checklist
Before starting: check the stock, guard and depth of cut
In our labs:
Check for nails, screws, loose knots, splits and other defects. Do not feed wood containing metal; ask the instructor about defective or unstable stock.
Use stock at least 1/4 inch thick and 10 inches long. These minimums do not make an otherwise unstable setup acceptable.
Set the infeed table for no more than 1/16 inch removal per pass, with the machine isolated for setup.
Check that the swinging cutterhead guard covers the cutter and returns freely. Do not use a setup that defeats it.
Plan the feed with the grain, with a cupped face concave-side down so the board does not roll. Have the instructor check stock that will not sit stably.
Have push blocks ready. Turn on dust collection and open the machine's collection gate before cutting.
Keep hands 4 inches away and transfer pressure with push blocks
Keep hands 4 inches away and transfer pressure with push blocks
In our labs, keep hands at least 4 inches from the cutterhead and never pass hands over it. Do not hook fingers around the end or side of the board. Use push blocks or the trained push-assist device; plan hand transfers before starting.
Stand to the side of the board near the cutter, not behind its feed line. Start the jointer and wait for full speed.
Feed with slight, even pressure against the table and fence. Keep the board stable rather than forcing it flat.
Once the leading portion has passed the cutter by more than the 4-inch margin, use the push block to apply downward pressure on the outfeed side. Transfer hands without passing them over the cutterhead.
Complete the pass while maintaining control and clearance. Let the guard return over the cutter before lifting the board away.
If the board kicks back or control is lost: stop the jointer
If the board kicks back or control is lost: stop the jointer
The cutter can throw a board opposite the feed direction. Do not chase it or reach toward the cutter. Stop the jointer from a safe position and notify the instructor before another pass.
Before starting: secure the bit, work and vise; Checklist
Before starting: secure the bit, work and vise
Select a bit and spindle speed suitable for the material and hole diameter. Have the instructor confirm an unfamiliar setup; a list of bit types is not approval to use every type in this press.
With the machine isolated for setup, seat and tighten the bit using the installed chuck's procedure. The chuck key never leaves your hand. It is not released until it is out of the chuck. Do not count on a key ejecting itself (see the chuck-key rule).
Clamp wood and metal to the table, or grip the work in a vise secured to the table. Secure small parts in a suitable vise or fixture; clamp larger parts with adequate support. Handholding is not workholding.
Check that the bit's full travel clears the table, vise and clamps. For a through-hole, provide clearance beneath the work or suitable sacrificial backing.
Secure the table at the required height and check that the work cannot rotate or lift when the bit catches.
Feed steadily and keep hands away from the rotating work
Feed steadily and keep hands away from the rotating work
A bit can catch and turn an unsecured part into a spinning lever. That is why a vise must be secured as well as tightened around the work.
Start with the bit clear of the work. Feed steadily so it cuts without being forced.
Ease the feed as the bit breaks through the underside. Keep hands clear rather than reaching underneath to support the exit.
Withdraw the bit under control, then stop the spindle before releasing or moving the work.
Supporting detail: Addendum 16 — Why larger drills usually need fewer revolutions per minute.
If the bit breaks or the part comes loose: stand clear
If the bit breaks or the part comes loose: stand clear
Do not grab a spinning part. Step clear and stop the drill press using a safely reachable stop control. For a broken bit, use the emergency stop if safely reachable. Wait for motion to cease and notify the instructor; do not restart until the fault and workholding have been checked.
In VCarve: match the material, preview the paths, then post
In VCarve: match the material, preview the paths, then post
Create or open the .crv job. Measure the material and match its width, height, thickness and units. In the lab's demonstrated setup, XY zero is the bottom-left corner and Z zero is the material surface.
Import the DXF vectors, remove unwanted geometry and join the outlines needed for the paths. Leave space for clamps and check the actual cutter path against their positions.
Create the pocket and profile toolpaths. Match the selected tool to the installed cutter; check cutting depths, feeds and speeds. Plan tabs or other workholding so the cut pieces remain secured.
Preview all toolpaths in their cutting order: pockets first, outside profiles last in this workflow. Check the first cutting location, remaining tabs, cut depth and clearance above clamps.
Save the intended toolpaths with the demonstrated Axiom HHC CNC (mm) (*.mmg) post processor and transfer the .MMG file to the supplied USB drive. Confirm the file selected at the machine is the one you previewed.
The preview checks the programmed cut; it does not prove that the real clamps are clear. The material position and zero settings at the router must match the job.
Before running: secure the cutter, material and every cut piece; Checklist
Before running: secure the cutter, material and every cut piece
With router power off and the machine made safe for tool setup, remove the magnetic dust boot. Check cutter insertion and tighten the collet with the appropriate wrenches, as demonstrated.
Use the installed power-up procedure, insert the USB drive, and select All axis home on the controller with the travel area clear. Homing finds the machine's references; it does not locate the workpiece.
Clamp the material on the spoilboard, the sacrificial surface above the machine bed. Keep clamps out of the entire tool path, leave the zero corner accessible, and tighten clamps progressively in the demonstrated zig-zag order.
Check that the material and the pieces cut from it will remain held throughout cutting. A loose piece can be struck and thrown by the cutter.
Set XY zero at the job's datum and Z zero at the material surface, using the demonstrated touch-off or tool-setting puck method. Clear the puck and its cord from the tool's path after setting.
Raise the router as demonstrated, refit the dust boot, turn on router power, open the dust-collection gate and start dust collection.
Keep clear of the cutter and the moving carriage throughout operation. The dust boot helps collect debris; it does not make the cutting area safe to reach into.
At Run, check the spindle and first movement against the preview
At Run, check the spindle and first movement against the preview
In our lab's demonstrated controller workflow, press RUN/PAUSE, choose UDisk File, select the intended .mmg file and review SetWorkParam. Confirm the parameters with the checkout instruction before accepting them. Accepting starts a countdown, followed by spindle startup and travel to the first toolpath location.
If the spindle does not start or the first location is wrong, press STOP/CANCEL. Resolve the cause with the instructor before restarting. Do not reach in to change the router switch while the program continues moving.
In our labs, watch the process and listen for unusual noises. Keep the controller accessible. Use STOP/CANCEL for a problem with the run or the emergency stop for an emergency, as demonstrated during checkout. Notify the instructor and use Lab Conduct and Emergencies when needed.
After cutting, switch off the router before removing the work
After cutting, switch off the router before removing the work
In our lab's sequence, turn router power off, wait for the cutter to stop, raise it to the demonstrated Z clearance, and remove the dust boot before unclamping and removing the workpiece. Refit the dust boot afterward.
Cut the retaining tabs using an approved tool and its own operating procedure; the lab instruction advises against popping the parts out. Stop dust collection when it is no longer needed, return tools and clamps, and complete shutdown and cleanup.
Safety/Equipment
Manual Lathe
Check workholding and material support before starting; keep clear of the rotating work and stop for hazardous chip strings.
Manual lathe: Category 3 in the Metals lab
Manual lathe: Category 3 in the Metals lab
A lathe rotates the workpiece against a cutting tool. See Lathe Operations for chucks, work support and turning operations.
Check the setup and the material extending through the spindle; Checklist
Check the setup and the material extending through the spindle
In our labs, check the setup before starting the lathe.
Check that the chuck or other workholding grips the part securely and that the cutting tool is secured.
The chuck key never leaves your hand. It is not released until it is out of the chuck (see the chuck-key rule).
Check the support for long material, including material extending through the back of the spindle. In our labs, never run long, unsupported material through the spindle.
Check the planned movement of the tool and carriage against the chuck, workpiece and supports.
Locate the emergency stop and foot brake, and confirm how to operate them before starting.
A long unsupported bar can whip as it rotates. Support at the cutting end does not establish that the part behind the spindle is safe.
The whole workpiece rotates; chip strings can catch and cut
The whole workpiece rotates; chip strings can catch and cut
The chuck, workpiece and any material projecting from the spindle are rotating hazards. Apply the entanglement rules to the entire setup, including its back side.
In our labs, stop and clear long chip strings when they become a hazard. Never pull a chip string by hand. Use Metal Chips and Swarf for removal and cleanup. If long strings keep forming, have the instructor review the cutting setup before continuing.
If the work shifts or the setup behaves unexpectedly, stop safely
If the work shifts or the setup behaves unexpectedly, stop safely
Do not try to steady rotating work or catch a loose part. Use the stopping controls you were shown if you can reach them safely, keep clear, and notify the instructor. Use Lab Conduct and Emergencies for an injury or emergency.
Check workholding, cutter clearance and cutting settings; recognize the different categories for manual and CNC mills.
Manual mill: Category 3; CNC mill: Category 2 in the Metals lab
Manual mill: Category 3; CNC mill: Category 2 in the Metals lab
A vertical mill uses a rotating cutter to remove material held in a vise or clamps. See Vertical Mill Anatomy and Motion for the machine's parts.
The manual mill is Category 3 in the Metals lab; the CNC mill is Category 2 there. Use Equipment Categories and Supervision for the corresponding permission and supervision requirements.
Check clamping, cutter travel and cutting settings before the cut; Checklist
Check clamping, cutter travel and cutting settings before the cut
In our labs, check and recheck the workpiece clamping before beginning an operation.
Check the vise or clamps and the cutter's retention. Confirm the tool can follow the planned path without striking the workholding.
Identify the closing gaps between the moving table, workholding and machine frame. Keep the planned travel clear.
Check spindle speed, feed, depth of cut and width of cut for the planned operation.
Check coolant and slide lubrication as directed for the installed mill. Report low levels, damage or a maintenance need rather than adjusting the machine's sliding fits yourself.
A rotating cutter and a moving table create different hazards
A rotating cutter and a moving table create different hazards
The cutter can cut or catch what touches it; the table can close a gap against the column, vise or clamps. Keep clear of both the cutting area and the table's travel. CNC motion follows the program, so a pause in motion is not permission to reach in.
Use Machine Hazards and Housekeeping for stopping before measurements and for isolation before adjustments or maintenance. Use Metal Chips and Swarf for chip removal, including the required controls if compressed air is used.
If a tool breaks or the work comes loose, step away
If a tool breaks or the work comes loose, step away
In our labs, step away if a tool breaks or the workpiece becomes loose. Stop the mill if it is safe to do so; do not endanger yourself to reach a control. Notify the instructor in every case.
Keep hands away from the cutting nozzle and clear of its travel. The jet cuts material, and the moving head can trap a hand. See Machine Hazards and Housekeeping for movement, guards and stopping. OMAX safety information is further reading for the installed-machine training.
Prepare the file and toolpath: lab steps 1–10
Prepare the file and toolpath: lab steps 1–10
This is our lab's OMAX operating sequence. Follow it with the machine-specific instruction you received at checkout.
Export the CAD file to DXF or DWG, as for a laser-cut part.
Turn on the OMAX machine.
Turn on the water: the top water line under the sink.
Open ProtoMAX Layout software.
Click File → “Open file for other CAD software.”
Use the move, rotate and duplicate tools to lay out the parts. One square is equal to one inch.
Click Autopath to create toolpaths. Check that the path cuts on the correct side of each line and cuts inside items before outside items, so the part is not cut loose before its interior features are cut.
Click Post.
Select the starting position, normally the bottom left.
Save the post. It saves as an .omax file.
Verify settings, follow the prompts and dry-run: lab steps 11–15
Verify settings, follow the prompts and dry-run: lab steps 11–15
Right-click on Post and open the .omax file in ProtoMAX Make.
When Make asks for cutting parameters, select the appropriate material and enter its thickness. The lab procedure says to oversize the thickness “by just a bit”; confirm that allowance with the instructor.
If the machine was just turned on, Make shows a red homing button at the top of the screen. Make sure nothing obstructs the nozzle's movement before clicking it to home the machine.
Follow all the on-screen steps. These include, but are not limited to:
Attaching the abrasive hose.
Testing the nozzle for abrasive flow.
Placing and securing the material.
Homing the nozzle to the starting position on the material.
Adjusting the water height if necessary.
Dry-running the program.
Flipping down the splash guard.
Run the program.
In step 14, “homing” to the material means the job's starting position; it is distinct from the machine-homing step in step 13. Have both positions demonstrated during checkout.
A dropped part or a fault needs a safe stop, not a reach into the tank
A dropped part or a fault needs a safe stop, not a reach into the tank
Do not reach into the cutting area to retrieve a part while the machine is operating. If the material moves or the cut behaves unexpectedly, keep clear and use the stopping procedure demonstrated during checkout. Notify the instructor; follow Lab Conduct and Emergencies for an emergency.
The lab sequence above ends at running the program. Have the instructor demonstrate shutdown and safe part recovery before using the machine; a part falling into the tank is not a recovery procedure. Use Equipment Operating Procedure for the general shutdown and reporting requirements.
Safety/Equipment
Prusa 3D Printers
Obtain project approval, match the sliced file to the printer and filament, and physically check the machine before setting it ready.
3D printers: Category 1 in the Rapid Prototyping Center
3D printers: Category 1 in the Rapid Prototyping Center
These printers build parts from filament, layer by layer. See 3D Printing from CAD for preparing a model and FDM 3D Printing for the printing process.
Get the project and material approved before printing
Get the project and material approved before printing
In our labs, a DET faculty member must approve a 3D-printing project before it starts. A project assigned by DET faculty needs no separate project approval, but must stay within its own guidelines and all RPC rules.
For approval, explain what the item is, where its design came from, how it will be made, the material amount and source, and its intended use; supply the digital file through the instructor's designated channel.
No personal material without prior approval.
No weapons, weapon-like items, weapon components, ammunition, dangerous materials or drug paraphernalia.
No commercial use. Class projects take priority over personal projects.
Slice for the selected printer, then check it in person; Checklist
Slice for the selected printer, then check it in person
In PrusaSlicer, arrange and orient the model. Select the printer and filament, and set supports, infill and brim as needed. Slice, review the preview, material use and estimated time, then export the .gcode or .bgcode file.
Use the lab's private job-identification instructions to name the file. In Prusa Connect, select a printer matching the type used when slicing.
Check that printer's queue before uploading the file. In our labs, talk with the uploader before deleting a named job you think is no longer needed.
Upload the file to the selected printer's dashboard, or use the guide's Send to Connect workflow from PrusaSlicer.
Before choosing Set Ready and Print Now, go to the machine and check:
The build plate is clear.
The loaded filament type matches the sliced file.
There is enough filament for the job.
If you are unsure the machine is ready, choose Add to print queue and check it before setting it ready later.
Hot surfaces and moving parts remain hazards during remote printing
Hot surfaces and moving parts remain hazards during remote printing
The nozzle and heated bed can burn, including after motion stops. Let them cool before handling the finished print or build plate. Keep hands and tools out of the printer's moving area; use Machine Hazards and Housekeeping for the general movement and isolation rules. See Prusa's hot-part precautions for further reading, not permission to service lab equipment.
The lab guide uses Prusa Connect or its app to monitor progress. A remote status display does not replace the physical readiness check. Set Ready can release the next queued job, so use it only after checking the machine and clearing the work area.
When your print is finished and safe to handle, remove it, check the plate and material again, and set the printer ready for the next job. Remove scrap and purged filament, return tools and leave the work area tidy.
Report jams and faults; do not repair the printer yourself
Report jams and faults; do not repair the printer yourself
In our labs, report jams, malfunctions and other technical problems to DET faculty. Do not try to fix equipment yourself. Stop a failing print using the controls covered in your training, and do not set a faulty printer ready for another job.
The student guide permits resetting an offline printer only when it is not currently in use. If you cannot establish that, or if a fault remains, report it rather than repeatedly resetting. Use Lab Conduct and Emergencies for an injury or emergency.
Materials and Manufacturing Processes/Foundations
What Is Manufacturing?
Turn materials into useful products by choosing processes that fit the material, quantity, cost and required quality.
Manufacturing turns materials into useful products
Manufacturing turns materials into useful products
Manufacturing changes materials into parts and products people can use. A board becomes a shelf, plastic pellets become a bottle, and metal sheet becomes a bracket. Shape, properties, joints and surfaces all contribute to the result.
A process is an operation that makes one of those changes. Most products need several processes. A useful plan states what each operation must achieve and how the result will be checked.
Primary processing makes usable material; secondary processing makes parts
Primary processing makes usable material; secondary processing makes parts
Primary processing converts raw resources into usable materials and common supply forms. Secondary processing turns those materials into parts or products. Stock means material supplied for further work, such as sheet, rod, boards or pellets.
Metal
Ore is refined into metal and made into stock such as sheet; sheet is then cut and bent into a bracket.
Plastic
Chemical feedstocks are made into polymer resin, often supplied as pellets; pellets are then molded into a bottle cap.
Wood
Logs are sawn into lumber; boards are then cut, joined and finished as furniture.
Glass
Mineral ingredients are melted and made into sheet glass; sheets are then cut and edge-finished for a window.
These terms describe a material's place in the supply chain. They do not replace the five process categories: sawing a log and sawing a furniture part are both separating.
Supporting detail: Addendum 17 — Why the boundary needs context.
Choose a process that fits material, quantity, cost and quality
Choose a process that fits material, quantity, cost and quality
Material
Can it tolerate the heat, force or chemical exposure? A process that bends metal sheet may crack a ceramic plate.
Quantity
A few parts favor flexible methods with little dedicated tooling. Repeated production can justify a mold or other tool made specifically for that part.
Cost
Count material, setup, tooling, labor, processing time, scrap and inspection. Cheap starting material can be expensive to turn into an acceptable part.
Required quality
Specify dimensions, allowable variation, strength and surface condition. Choose a route that can meet them consistently, then verify it.
For a small plastic cover, 3D printing may be useful for a few trial pieces; molding may suit repeated production after the design settles. Neither route wins from quantity alone: material behavior, geometry and acceptance requirements still matter.
Prototype, batch and mass production describe production situations, not universal numerical cutoffs. Manufacturing economics and design for manufacturing develop this comparison further.
Characteristics: What is the material like? Compare properties, useful forms and limitations.
Forming: How can it take a shape?
Separating: How can material be removed or cut apart?
Fabricating: How can parts be joined?
Conditioning: How can its internal properties be changed?
Finishing: How can its surface be protected or improved?
This is the collection's learning map for the later plastics, wood and metals topics. Characteristics is the starting description, not a sixth process category.
The map is not a mandatory factory sequence. Wood may be dried before cutting; a metal part may be annealed between forming steps; some surfaces are finished before assembly. A product may repeat a category or omit one.
Materials and Manufacturing Processes/Foundations
Manufacturing Process Categories
Classify an operation by its main purpose: separating, forming, fabricating, conditioning or finishing.
Five categories describe the change an operation makes
Five categories describe the change an operation makes
Name the operation's intended result. Are we removing material, creating shape, joining parts, changing internal properties or treating a surface?
These are five kinds of change, not five steps that every product must follow in order.
This collection uses the course's five-category model. In this model, forming includes casting, molding and additive manufacturing such as 3D printing. Other technical references may separate those into their own process groups.
Separating removes material to make a size, shape or opening
Separating removes material to make a size, shape or opening
Separating cuts material apart or removes it from a workpiece, the piece being worked on. Look for a cut edge, hole, slot or reduced dimension as the intended result.
Sawing: cut a wooden board or plastic rod to length.
Drilling: remove material to make a hole in a metal bracket or wooden panel.
Milling: a rotating cutter removes material to make a flat face, pocket or slot.
Laser cutting: remove material along a narrow path to cut a suitable sheet material.
Supporting detail: Addendum 18 — A laser cut does not have to vaporize all the removed material.
Forming creates shape without using material removal as the shaping method
Forming creates shape without using material removal as the shaping method
Forming gives material a shape by filling a mold, deforming it or building it up. The central action creates the shape rather than cutting unwanted material away.
Casting and molding: pour metal into a mold, mold a plastic cap, or cast a concrete planter.
Bending: bend sheet metal into a bracket or bend prepared wood around a form.
Forging: press or hammer metal into a new shape.
3D printing: build a plastic part in layers.
Forming can still produce excess material. Trimming a molded edge or cutting away printed supports is a separate separating operation. “Forming” does not promise zero waste.
Fabricating joins parts into an assembly
Fabricating joins parts into an assembly
Fabricating brings separate parts together so they work as one assembly. Ask whether the intended result is a joint.
Welding: join metal frame members or suitable plastic parts.
Adhesive bonding: glue wooden strips together or bond a panel to a frame.
Fasteners: use screws, bolts or rivets to hold parts together.
Joinery: assemble matching wooden joint features, such as a mortise and tenon.
Cutting the joint features is separating; fitting and securing the parts is fabricating. In industry, “fabrication” can describe a whole production job. Here it has the narrower meaning joining.
Conditioning changes internal properties
Conditioning changes internal properties
Conditioning changes how the material behaves through its structure, moisture content or chemical state. A new outline or a decorative coating is not its main goal.
Heat treating: use a controlled heating and cooling cycle to change properties of a suitable metal.
Drying or seasoning wood: reduce moisture content before later processing or service.
Curing: allow a resin's chemical reaction to develop its intended properties.
Annealing: use a controlled thermal cycle to relieve stress or change structure, as appropriate to the metal, plastic or glass.
Conditioning can also change dimensions. Drying wood may shrink; heat treatment may distort a part. “Changes properties” does not mean “leaves every dimension unchanged.”
Finishing treats the surface for protection or appearance
Finishing treats the surface for protection or appearance
Finishing changes surface condition, appearance or protection. It may add a layer, remove a little material or alter the surface itself.
Painting: coat a wooden panel or metal housing.
Plating: deposit a metal layer on a part.
Staining: change wood's color; stain alone does not necessarily provide a protective film.
Polishing: improve the surface of metal, suitable plastic or glass.
A surface location alone does not decide the category. Surface hardening primarily changes material properties, so it belongs under conditioning in this model.
For overlapping processes, state the purpose and pick the primary category; Practice
For overlapping processes, state the purpose and pick the primary category
Identify one operation. Break a long manufacturing description into separate actions.
State its acceptance goal. What result tells you this operation is complete?
Choose the category that best matches that goal. Name any secondary effect in the explanation.
Sanding
Sanding a block down to a specified thickness is primarily separating. Sanding out visible scratches before a clear coat is primarily finishing, although both remove material.
Bent lamination
Bonding thin wood layers around a curved form combines fabricating and forming. If the stated goal is the curve, call forming primary; if the question focuses on the bond between layers, call fabricating primary.
Resin and adhesive curing
Curing a resin part to develop properties is conditioning. Bonding two parts with that resin is primarily fabricating; curing is the property-changing step that enables the joint.
Welding
A weld can change nearby material properties, but a step intended to join two frame members is primarily fabricating.
If the description only says “sanding” or “curing,” explain what purpose you are assuming. A defensible classification includes the reason.
Compare exactly four families: Metals, Plastics (polymers), Wood & Composites, and Ceramics & Glass.
Use four material families as the starting point
Use four material families as the starting point
The course uses exactly four families: Metals; Plastics (polymers); Wood & Composites; Ceramics & Glass. A family helps you predict useful behavior. It does not specify a material well enough to manufacture a part.
Classify the material in the named part, not the entire product. A kettle can have a metal body, a plastic handle and a glass window.
Supporting detail: Addendum 19 — Why another book may show a different family list.
Metals combine useful strength, stiffness and conductivity
Metals combine useful strength, stiffness and conductivity
Metals include metallic elements and alloys, mixtures designed for useful properties. Steel, aluminum and copper are everyday examples.
Many metals conduct heat and electricity well and can deform permanently without breaking. Many are strong and stiff compared with unreinforced plastics. Density varies: aluminum is much less dense than steel, so “metal” does not always mean the heaviest choice.
Typical matches include copper wire for electrical conduction, aluminum cookware for heat transfer, and steel fasteners for carrying loads. Corrosion behavior depends on the alloy and environment. Rust specifically concerns iron-containing materials; other metals can corrode without rusting.
Metals may be cast, formed, cut, joined, heat treated and coated. Those process choices depend on the specific alloy and condition. Detailed metal processing belongs in the later metals topics; Milling Operations and Lathe Operations show separating operations.
Plastics are usually light, moldable and poor conductors
Plastics are usually light, moldable and poor conductors
Plastics (polymers) are materials based on long molecular chains, usually with additives to adjust their behavior. Polyethylene containers, acrylic display panels and nylon gears belong here.
Common unfilled plastics have relatively low density and low thermal and electrical conductivity. They can range from flexible to rigid, and from tough to brittle. Heat, sunlight and chemicals affect different grades differently.
Thermoplastics can soften on heating and be reshaped under suitable conditions. Thermosets develop a chemically linked structure during curing and cannot simply be remelted into a new shape.
“Light” does not mean “floats.” Solid acrylic is denser than water. A hollow product may float because its overall density includes the trapped air.
Supporting detail: Addendum 20 — A supplier value that checks the floating claim.
Wood & Composites depend on grain, layers and reinforcement
Wood & Composites depend on grain, layers and reinforcement
Wood has a cellular structure and grain. It is often light for its useful stiffness, relatively easy to cut and join, and a poor heat conductor. Strength and movement depend on direction and moisture content.
A composite combines materials so they work together. Examples include plywood, wood-fiber board, glass-fiber-reinforced plastic and carbon-fiber-reinforced plastic. The material surrounding and holding reinforcement is the matrix; the reinforcement helps carry load.
Do not assume every composite behaves like wood or like unfilled plastic. Fiber direction, layer arrangement, binder and moisture exposure affect the result. A composite can offer useful strength or stiffness for its mass while still being difficult to cut, join or repair.
Plywood shelves and glass-fiber-reinforced boat panels belong to the same course family, but need different processing choices. Later wood topics develop grain and moisture behavior.
Ceramics & Glass often resist heat and wear but can fracture abruptly
Ceramics & Glass often resist heat and wear but can fracture abruptly
Ceramics & Glass include fired clay products, porcelain, window glass and engineering ceramics such as alumina. Many are hard, resist chemical attack and carry compression well. Many also have little ability to deform permanently before fracture.
A tile can resist scratching yet break when struck. Hardness is not toughness. Many familiar ceramics and glasses are electrical insulators, but the family contains exceptions; thermal conductivity also varies widely.
Shaping may occur before firing, while hot, or through suitable cutting and grinding afterward. Glass can be formed while hot and annealed to reduce residual stress. Finished ceramic parts are often harder to machine than common metals or plastics.
Supporting detail: Addendum 21 — Hard to machine does not mean impossible to machine.
Compare typical behavior, then check the specific material; Practice
Compare typical behavior, then check the specific material
Common tendencies, not design values or a ranking from best to worst. Compare materials at the same temperature, condition and loading direction.
Use Material Properties to put a precise name to the requirement. Then select a grade, species or composite construction and check its data. No family wins on every property.
Distinguish strength, stiffness, hardness and toughness, then compare physical and chemical behavior, cost and workability.
State the requirement before choosing the material
State the requirement before choosing the material
“Strong,” “light” and “durable” are starting points. A useful comparison says what load, temperature, environment and lifetime the part must handle.
Mechanical properties describe behavior under force. Physical properties describe features such as density and heat or electrical behavior. Chemical properties describe interaction with the environment. Cost and workability determine whether a suitable material can become a practical product.
Start with the four material families, then compare actual materials within them. Processing and condition matter: a material name alone does not tell you its final properties.
Strength describes the stress a material can withstand before a specified limit, such as permanent deformation or fracture. Stress relates force to the area carrying it. A thicker part may carry more load without being made of a stronger material.
Tensile strength
Resistance to a pulling load. Think of a tie rod being pulled along its length.
Compressive strength
Resistance to a pushing or crushing load. Think of a block squeezed between two surfaces. A material good in compression may be much less capable in tension.
Stiffness
Resistance to elastic deformation, the change that recovers when the load is removed. A shelf that sags too far may be strong enough to avoid failure but insufficiently stiff.
A part's stiffness depends on both its material and its geometry. Compare similarly shaped specimens when comparing materials; do not infer material stiffness by comparing a thin wire with a thick bar.
Supporting detail: Addendum 22 — Stress, strain and modulus give the comparison units.
Hardness, toughness, brittleness and ductility answer different questions
Hardness, toughness, brittleness and ductility answer different questions
Hardness
Resistance to local indentation or scratching, depending on the test. It can help resist wear, but hardness alone does not determine wear performance.
Toughness
Ability to absorb energy before fracturing. A part that must survive a blow needs more than a hard surface.
Brittleness
A tendency to fracture with little permanent deformation. Glass may resist scratching but crack instead of bending permanently.
Ductility
Ability to deform permanently in tension before fracture. A ductile metal can be drawn into wire. Elastic stretch that disappears when unloaded is not the same as ductility.
Do not treat these as synonyms. A hard ceramic tile can be brittle; a ductile metal can bend before it breaks. Toughness depends on both the stress sustained and the deformation before fracture, as well as test conditions.
Supporting detail: Addendum 23 — Why a single “toughness number” needs its test method.
Density and thermal behavior decide weight and temperature limits
Density and thermal behavior decide weight and temperature limits
Density
Mass per unit volume. At equal volume, lower density gives lower mass. A large hollow metal part can weigh less than a small solid plastic part, so compare the whole design too.
Melting point or melting range
The temperature or range where a material melts. It helps choose processing conditions, but it is not the allowable service temperature: a loaded part may lose useful stiffness or strength earlier.
Thermal conductivity
How readily heat travels through a material. A heat spreader benefits from high conductivity; an insulating handle usually benefits from low conductivity.
Electrical conductivity
How readily electric current passes through a material. A wire needs a conductor; its surrounding insulation needs low conductivity under the intended conditions.
Many common metals conduct heat and electricity well. Many unfilled plastics, dry woods and familiar ceramics are poor electrical conductors. Additives, moisture and temperature can change those tendencies.
Supporting detail: Addendum 24 — Not every material has one useful melting-point number.
Corrosion resistance is resistance to a particular environment
Corrosion resistance is resistance to a particular environment
Corrosion resistance is the ability to resist chemical or electrochemical deterioration in service. A metal that works well indoors may perform differently in salt water or against another metal.
Rust is one form of corrosion involving iron. Aluminum and stainless steel can resist many exposures, but neither is immune to every environment. Coatings can protect a surface, and their condition matters.
For plastics, wood and composites, also consider chemical attack, sunlight, moisture and decay as appropriate. “Does not rust” is not the same as “will last outdoors.” Name the exposure before selecting a family or grade.
Cost and workability belong in the same comparison
Cost and workability belong in the same comparison
Workability means how readily a material can be processed into an acceptable part. It is specific to the operation: a material that molds well may be difficult to bond, and one that cuts readily may be unsuitable for bending.
Cost includes more than price per mass. Consider how much material the design needs, available supply forms, tooling, processing time, waste, inspection and any protective finish.
A family profile narrows the search: common metals often offer stiffness and conductivity; plastics often offer low mass and moldability; wood and composites offer useful directional performance; ceramics and glass often offer hardness and chemical resistance. The particular material decides whether those benefits meet the job.
Use Manufacturing Process Categories to describe the required operations. Detailed manufacturing economics and design for manufacturing extend the cost comparison.
Choose a candidate, give a reason, and name what still needs checking; Checklist; Practice
Choose a candidate, give a reason, and name what still needs checking
Write the required function and service conditions.
Name the properties that control success.
Screen the four families, then identify a specific candidate material.
Check direction, temperature, moisture, processing condition and data source.
Check workability and total cost, then verify the finished part against its requirements.
For a heat-spreading plate, Metals is a sensible starting family because common choices such as aluminum and copper conduct heat well. The next checks include temperature, dimensions, corrosion exposure and cost. That is a justified candidate, not a complete design specification.
Identify an additive process by what it places, what joins the material, and what the part still needs after the build.
Classify the mechanism before comparing process names
Classify the mechanism before comparing process names
Additive manufacturing builds three-dimensional geometry by adding material. The standard process families describe how material is placed and joined. They are different from this course's five purpose categories, which describe what an operation is intended to accomplish.
Use three questions when you meet an unfamiliar name: What feedstock enters?What places or selects each region?What joins or solidifies it? Then ask what must happen after the build before the part is ready to inspect or use.
For the course's purpose model, additive shape-building is primarily Forming. Removing supports is a later Separating operation; curing or heat treatment can be Conditioning; finishing can change a surface. The seven AM families below do not replace those five purpose categories.
Seven families place and join material in different ways
Seven families place and join material in different ways
Family
Feedstock and joining mechanism
A useful boundary
Material extrusion
Material is pushed through a nozzle and selectively deposited. A common filament route softens thermoplastic, then adjacent roads bond as they cool.
FDM is a registered trademark of Stratasys; FFF is generic usage for filament fabrication. Neither name covers every extrusion feedstock.
Vat photopolymerization
Light selectively cures liquid photopolymer held in a vat. SLA, DLP and masked exposure systems select regions differently.
Cleaning, support removal and material-specific post-curing may remain. “Resin printing” does not identify one universal exposure method.
Powder bed fusion
A thin powder layer is spread, then thermal energy selectively fuses regions. Polymer SLS uses a laser; HP Multi Jet Fusion applies agents and heat. Metal routes use laser or electron-beam energy.
Polymer and metal PBF share a family, not one identical workflow. Loose powder can support polymer SLS parts, while some metal routes need supports for anchoring or heat flow; process-specific exceptions exist.
Binder jetting
A printhead selectively deposits binder into a powder layer. Repeating the powder-and-binder cycle produces a fragile green shape.
The printed shape is not automatically a finished dense part. Curing, depowdering, debinding, sintering or infiltration depend on the material and route.
Material jetting
Droplets containing build material are selectively deposited, then solidified or cured. PolyJet is a Stratasys photopolymer-and-UV example.
The jetted liquid is build material, not merely binder placed into a powder bed. PolyJet is one branded implementation, not the family name.
Directed energy deposition
Powder or wire is delivered to a target while focused energy creates a local melt zone. Deposited tracks solidify on a substrate or existing part.
The feed arrives at the deposition point rather than being spread as a complete powder layer. Repair and large features are useful contexts; finishing and inspection still matter.
Sheet lamination
Sheets are bonded to build thickness, with shape developed layer by layer.
The family name alone does not establish the sheet material, bonding method, accuracy or present-day machine capability.
Material names do not move freely between families. A printer, process version and qualified feedstock must be considered together. Polymer, metal, ceramic, composite, sand and cementitious examples exist in particular systems; that does not mean every material works in every printer.
Powder and droplets can play three different roles
Powder and droplets can play three different roles
Similar words do not mean the same mechanism. Follow what the droplets contain and when the material becomes the intended solid.
Powder bed fusion
The powder is the build material; selected regions are thermally fused during the build.
Binder jetting
The powder is the build material; jetted binder holds a green shape that may require later densification.
Material jetting
The droplets themselves contain build material; a separate support material may also be deposited in some systems.
HP Multi Jet Fusion belongs with powder bed fusion because agents help control where powder is fused by heat. It is not binder jetting simply because a printhead deposits an agent. See the manufacturer's mechanism comparison for that distinction.
The build is one stage of the manufacturing route; Checklist; Practice
The build is one stage of the manufacturing route
Judge a route from feedstock through the inspected part, not from the printer alone. Depending on the family and material, the route may include cooling, unpacking and depowdering; washing and post-curing; support removal; debinding and sintering; heat treatment; machining; surface finishing; or inspection.
State the material, required geometry, load direction, critical surfaces and fit.
Identify what carries an overhang during the build and whether that material can be removed afterward.
Trace trapped powder, uncured resin, support material or internal passages to an exit or cleanup method.
Name the state at the end of the machine cycle: finished solid, green part, supported part, powder-filled part or another intermediate state.
List the post-build and inspection steps required before the part can meet its intended requirement.
No family is the universal best choice. Surface, accuracy, properties, cost and throughput depend on the actual material-process-machine combination, build use, postprocessing and acceptance requirements. Continue to FDM 3D Printing for the material-extrusion mechanism and 3D Printing from CAD for the filament CAD-to-slicer workflow.
Follow the shared powder-layer cycle, then distinguish polymer SLS and MJF from stated metal laser and electron-beam routes.
Powder bed fusion repeats a spread, select, and lower cycle
Powder bed fusion repeats a spread, select, and lower cycle
Powder bed fusion (PBF) is one additive-manufacturing family. A machine spreads a thin powder layer, applies thermal energy to selected regions, lowers or advances the build, and repeats. Unselected powder remains around the growing parts until they are unpacked.
The family name does not specify one material or energy source. Polymer and metal examples can share the layer cycle while differing in temperature, atmosphere, thermal behavior, support strategy, cooldown, powder recovery, postprocessing and inspection.
Start with Additive Manufacturing Process Families for the seven-family map. PBF thermally fuses powder during the build; it is not binder jetting, where deposited binder first creates a green shape.
Supporting detail: Addendum 26 — Readable process sources.
Polymer SLS and MJF select powder in different ways
Polymer SLS and MJF select powder in different ways
Selective laser sintering (SLS)
A laser scans selected regions of a polymer powder layer and thermally joins the particles. Unfused powder surrounds the parts in the stated process, so dedicated support structures are generally unnecessary; the build must cool before unpacking and depowdering.
Multi Jet Fusion (MJF)
A printhead places fusing and detailing agents on polymer powder, then applied heat fuses selected regions. The agents control fusion; they are not binder that leaves a green part for later sintering.
Both examples belong to PBF because powder is thermally fused during the build. Neither description proves that any polymer powder, color, wall, gap or enclosed cavity will work on a particular machine.
Loose powder can carry surrounding geometry during these stated polymer builds, but it must still be removed. A sealed hollow region can trap powder. An internal passage needs an accessible route for cleaning and inspection; “no dedicated supports” does not mean “no design constraints.”
Metal laser and electron-beam PBF need process-specific thermal reasoning
Metal laser and electron-beam PBF need process-specific thermal reasoning
The metal examples here use a laser or electron beam to melt or fuse selected regions of metal powder. The part develops through repeated melt-and-solidify events, so orientation and connection to the build system can affect heat flow, residual stress, distortion and later removal.
In a stated laser PBF case, sacrificial supports may anchor an overhang to the build plate and conduct heat away. Loose metal powder surrounding the part is not automatically an adequate thermal path. That does not create a universal rule that every metal PBF system and geometry needs the same supports.
Electron-beam PBF has process-specific strategies and exceptions. Current commercial examples can reduce or replace traditional supports for some parts. Record the exact machine, material, melt strategy, orientation and acceptance plan instead of transferring one support rule to every metal powder process.
Supporting detail: Addendum 27 — Why the support statement is qualified.
Design powder access and the post-build route with the part; Checklist; Practice
Design powder access and the post-build route with the part
The layer cycle is shared; support, thermal and post-build assumptions are material- and process-specific. Geometry must allow powder removal and inspection.
Mark enclosed volumes, channels and lattice spaces; give loose powder a stated removal and inspection route.
State the material, machine/process variant, energy route and build orientation rather than writing only “PBF.”
Identify what supports geometry and, for the stated thermal case, what anchors the part and conducts heat.
Plan cooldown, unpacking, depowdering and any support removal before choosing inaccessible geometry.
List required postprocessing and inspection. A completed build is not automatically a qualified service part.
Polymer chains, thermoplastics and thermosets, common plastics, and what resin identification codes actually tell you.
Plastics get their behavior from polymer chains
Plastics get their behavior from polymer chains
A polymer is a substance made of very large molecules built from repeating units. Small starting molecules called monomers react to build those molecules. Many polymers have long chains; some also have branches or chemical links between chains.
A plastic combines a polymer with ingredients that may change its color, flexibility, processing behavior or resistance to weather. The polymer name is a starting point, not a complete material specification. Two grades of the same plastic can behave differently.
Plastics is one of the four material families in the material-family foundations topic. A polymer reinforced with glass or carbon fibers is a composite; the course places composites in Wood & Composites.
Thermoplastics soften again; cured thermosets do not remelt
Thermoplastics soften again; cured thermosets do not remelt
The useful distinction is behavior on reheating
Type
What happens
Examples and recycling
Thermoplastic
Heating makes the material soft enough to reshape or flow. Cooling makes it firm again. Reheating can repeat this change, within the material's processing limits.
PE, PP, PVC, PLA, ABS, PETG, acrylic, polycarbonate and nylon. Clean, compatible material can often be remelted for recycling; contamination, degradation and available collection systems limit actual recovery.
Thermoset
Curing forms a network of chemical links between molecules. The cured material cannot be melted back into a moldable liquid. Excessive heating degrades it.
Cured epoxy and unsaturated polyester resin. They cannot be recycled by ordinary melt-and-remold processing; specialized recovery methods may exist.
Curing is a chemical change; cooling is a temperature change. A two-part epoxy becoming solid is not simply a hot plastic cooling down.
Supporting detail: Addendum 28 — Softening, melting and heat resistance are different questions.
Light weight and corrosion resistance come with limits
Light weight and corrosion resistance come with limits
Light weight: many unfilled plastics have much lower density than metals. Low weight does not automatically mean high stiffness.
Chemical resistance: plastics do not rust like steel, but a chemical may soften, swell or crack a particular plastic. Check the material, chemical, temperature and exposure time together.
Low softening or melting temperatures: many common thermoplastics are easy to form with heat but unsuitable for hot, loaded service.
Creep: slow deformation under a sustained load. A plastic shelf can keep sagging even when its load stays constant.
UV degradation: sunlight can discolor or embrittle susceptible grades. Outdoor service calls for a suitable resin and stabilization, not just a preferred color.
Electrical insulation: many unfilled plastics resist current flow. Conductive fillers and special formulations can change that behavior.
Supporting detail: Addendum 29 — Why a short strength test does not settle a long service life.
Match common thermoplastics to their useful properties
Match common thermoplastics to their useful properties
These are typical uses and tradeoffs, not design ratings for every grade. All materials in this table are thermoplastics.
Common plastics: a first selection, followed by a grade data sheet
Material
Typical uses and strengths
Watch for
PLA — polylactic acid
Models, packaging and filament; stiff, often made from renewable feedstocks.
Ordinary grades have limited heat resistance and can be brittle. Bio-based does not mean an item belongs in home compost or a recycling bin.
ABS — acrylonitrile butadiene styrene
Housings and toys; a useful balance of toughness and rigidity.
Ordinary grades weather poorly outdoors; some solvents attack it.
PETG — glycol-modified PET
Clear displays, formed packaging and filament; tough and readily thermoformed.
Scratches and limited service temperature. PETG is not interchangeable with bottle-grade PET.
Acrylic / PMMA — polymethyl methacrylate
Signs, displays and glazing; clarity, stiffness and good weathering.
More prone to cracking under impact than polycarbonate; vulnerable to some solvents.
PC — polycarbonate
Impact-resistant glazing and housings; transparent and tough.
Scratching and chemical attack; select an appropriate UV-resistant grade for outdoor exposure.
HDPE — high-density polyethylene
Bottles, tanks and pipe; tough with useful chemical resistance.
Low stiffness compared with metals, creep and substantial thermal expansion.
LDPE — low-density polyethylene
Film and squeeze bottles; flexible and tough.
Less stiff than HDPE and limited temperature capability.
PP — polypropylene
Containers, caps and living hinges (thin flexible connections); light and chemically resistant.
Creep, UV sensitivity in unstabilized grades and reduced toughness in cold service.
PVC — polyvinyl chloride
Rigid pipe and window profiles; plasticized grades make flexible tubing and cable insulation.
Properties depend strongly on additives; limited temperature range.
Nylon / PA — polyamide
Gears, bearings and cable ties; strength, toughness and wear resistance.
Absorbed moisture changes dimensions and mechanical properties.
Supporting detail: Addendum 30 — Material references for checking a particular choice.
Epoxy and polyester resin cure into thermosets
Epoxy and polyester resin cure into thermosets
Two common thermosetting resin systems
Resin
Typical uses and strengths
Limitations
Epoxy
Adhesives, cast parts and composite matrices; good adhesion and generally low cure shrinkage.
Mixing and cure conditions affect properties. Often costs more than general-purpose polyester resin; unprotected epoxy can degrade in sunlight.
Unsaturated polyester resin
Fiberglass boat shells and panels; economical for many composite parts.
Typically greater cure shrinkage and lower adhesive performance than epoxy. Cured resin cannot be remelted.
“Polyester” alone is ambiguous. PET packaging is a thermoplastic polyester. The unsaturated polyester resin used in a conventional fiberglass layup cures into a thermoset. See the hand-layup card in Plastic Forming Processes.
Supporting detail: Addendum 31 — Where the resin comparison comes from.
Resin codes identify plastic; they do not promise recycling; Practice
Resin codes identify plastic; they do not promise recycling
The number on a container is a resin identification code (RIC). It can help sorting, but it does not say whether the local recycling program accepts that product.
The seven code-to-resin matches, checked against current public guidance
Code
Plastic
1 — PET / PETE
Polyethylene terephthalate
2 — HDPE
High-density polyethylene
3 — PVC
Polyvinyl chloride (vinyl)
4 — LDPE
Low-density polyethylene
5 — PP
Polypropylene
6 — PS
Polystyrene
7 — OTHER
Resins outside the first six categories; also some combinations of resins. It is not one particular plastic.
For example, code 5 identifies PP; it does not prove that a PP lid is accepted with PP containers. Use the collector's instructions for that item. Do not assign PETG to code 1 just because its name contains PET.
Supporting detail: Addendum 32 — Verified code sources and the standard's exact distinction.
How eight plastic and composite processes shape material, what they can make, and where tooling and geometry limit the choice.
Start with the shape and how the material becomes solid
Start with the shape and how the material becomes solid
These processes make a shape by moving softened material, stretching sheet or curing resin in tooling. A mold shapes a part against its surfaces; a die gives flowing material a cross-section. Tooling is the equipment made specifically to produce the part.
Use the process-category foundations topic for the five-category framework. Here, follow what happens to the material: thermoplastics usually set by cooling; thermosets set by curing. Review Plastics as Materials if that distinction is unclear.
The starting form and the finished shape narrow the choice before cost enters the discussion. The diagrams show typical versions of each process.
Injection molding fills a closed cavity, then repeats the cycle
Injection molding fills a closed cavity, then repeats the cycle
In conventional thermoplastic injection molding, a heated barrel and screw prepare the melt. The screw advances to push a measured shot (the material delivered in one injection) through a nozzle into a clamped mold.
A thermoplastic cycle. Cooling overlaps filling and packing; the five labels describe the main jobs, not five completely separate thermal events.
Clamp: close the mold and hold it against the pressure of the incoming melt.
Inject: fill the cavity.
Hold/pack: maintain pressure to feed additional material as it shrinks, while the gate can still pass melt.
Cool: allow enough heat to leave for the part to keep its shape during removal.
Eject: open the mold and push the part free, commonly with ejector pins. Close for the next cycle.
Materials and products: thermoplastics such as ABS, PP and nylon become housings, caps, clips and gears. Specialized injection systems also mold thermosets; those require curing, so the cooling-based cycle above is not universal.
Tooling and quantity: detailed, pressure-resistant molds are a substantial initial investment. Repeated cycles and multiple cavities can make the investment worthwhile for many identical parts.
Supporting detail: Addendum 33 — See the machine and cycle in a public explainer.
Sprue, runner and gate carry melt into the part
Sprue, runner and gate carry melt into the part
In a conventional sprue-and-runner layout, the sprue receives melt from the nozzle, a runner distributes it, and a gate is the restricted entrance to a part cavity. One mold may contain several cavities, and one cavity may have several gates.
Draft is a slight taper on a surface in the mold-opening direction. It helps the part release instead of scraping along the tool. Injection molding can produce ribs, bosses (raised features around holes) and fine detail, but every feature must have a way out of the mold.
An undercut traps material behind a tool feature. It may require a moving side core, another special mechanism or a redesigned part. A simple two-part mold cannot produce every enclosed hollow shape.
Uniform walls reduce sink marks and uneven shrinkage; Practice
Uniform walls reduce sink marks and uneven shrinkage
Aim for a reasonably uniform wall thickness, with gradual transitions where thickness must change. A thick mass cools differently from an adjacent thin wall. Its shrinkage can pull the surface inward, leaving a sink mark, or contribute to distortion.
A solid block under a thin housing wall is therefore a warning sign. Hollow out the bulky region where possible and use appropriately sized ribs for support. Packing and cooling settings also matter; changing the drawing is not the only remedy.
Supporting detail: Addendum 34 — Three design clues to recognize.
Blow molding inflates a hot tube or preform into a hollow part
Blow molding inflates a hot tube or preform into a hollow part
A mold closes around a hot parison (tube), or a previously molded preform. Air pressure expands the material against the mold, then it cools. Extrusion blow molding starts with a tube; injection-based versions start with a molded preform.
Materials and products: thermoplastics; HDPE detergent bottles and PET beverage bottles are familiar examples made by different blow-molding variants.
Tooling and quantity: dedicated molds and machinery favor repeated production, especially large packaging runs. Mold complexity and the chosen variant affect cost; lower forming pressure does not make the whole production line inexpensive.
Geometry: good for thin-walled hollow containers. Stretching affects wall thickness; external detail is controlled better than internal detail. It does not directly make a solid gear or complex internal ribs. Mold parting lines, and pinch-off seams in extrusion-blown parts, may remain visible.
Supporting detail: Addendum 35 — Public process reference.
Rotational molding coats a mold to make a large hollow shell
Rotational molding coats a mold to make a large hollow shell
A measured charge, usually thermoplastic powder, goes inside a mold. Heating and slow rotation about two axes distribute material over the inside surface as it melts. The mold keeps moving during cooling before the shell is removed.
Materials and products: predominantly polyethylene; tanks, playground shells and kayaks.
Tooling and quantity: molds do not withstand injection pressure, so tooling is often less costly for a large part. Heating and cooling the mold takes time, making low-to-medium quantities attractive compared with faster processes.
Geometry: large hollow parts with relatively even walls are a strength. Local thickness, corners and fine tolerances still need care. Tiny details, very thin walls and solid precision parts are poor fits. This is slow coating of the mold, not high-speed centrifugal casting.
Supporting detail: Addendum 36 — Public process reference.
Thermoforming stretches a sheet into a tray or shell
Thermoforming stretches a sheet into a tray or shell
Heat thermoplastic sheet until it is pliable, form it against a tool, cool it and trim the edge. In vacuum forming, removing air between sheet and tool lets outside air pressure press the sheet against the tool. Pressure forming adds pressure on the other side.
Materials and products: thermoplastic sheets such as PETG, ABS and polystyrene; packaging trays, display covers and equipment liners.
Tooling and quantity: a simple one-sided tool can suit prototypes or short runs. Durable tools and automated equipment also support very large packaging volumes.
Geometry: best for open, sheet-like shapes with draft. Deep draws stretch and thin the sheet; the tool controls one surface most directly. It cannot create a solid boss or a closed bottle from one sheet in this basic process. Undercuts complicate release.
Supporting detail: Addendum 37 — Public process reference.
Extrusion makes a continuous, constant cross-section
Extrusion makes a continuous, constant cross-section
A screw moves and melts plastic, then pushes it continuously through a shaped die. Cooling and sizing equipment establish the final dimensions. The product is cut to length or wound.
Materials and products: commonly thermoplastics such as PVC and PE; pipe, tubing, sheet, film and window profiles.
Tooling and quantity: a profile die is often simpler than a complex injection mold, but the production line and setup still cost money. Long runs spread those costs over many meters of product.
Geometry: the die can make solid or hollow cross-sections. It cannot directly put a cap on the end of a tube or create isolated holes along one side; those require other operations. A long product with the same section everywhere is the main clue.
Supporting detail: Addendum 38 — Public process reference.
Compression molding presses a charge between matched tools
Compression molding presses a charge between matched tools
Place a measured amount of material in an open mold. Closing the heated tool applies pressure and spreads the charge into shape. With a thermosetting compound, the part cures before removal; cooling alone is not what hardens it.
Materials and products: often thermosets or fiber-filled thermosetting compounds; electrical components and composite body panels. Thermoplastic sheet composites can also be compression molded, with a cooling-based solidification step.
Tooling and quantity: matched tools and a press require investment, often justified by repeated medium-to-high production. Tooling is not automatically cheap; size, surface quality and precision matter.
Geometry: both faces can be shaped, including ribs and shaped panels. Material must flow before it cures; extremely thin features, deep narrow details and trapped undercuts are difficult.
Supporting detail: Addendum 39 — Public process reference.
Casting fills a mold with liquid resin for small quantities
Casting fills a mold with liquid resin for small quantities
Liquid resin fills a mold and hardens. In common small-batch resin casting, mixed components react and cure. A flexible mold made from a master pattern can reproduce surface detail.
Materials and products: often thermosets such as epoxy, polyurethane or unsaturated polyester; prototypes, decorative replicas and electrical encapsulation. Casting is broader than polyurethane casting; some cast plastics, such as cast acrylic, are thermoplastic after polymerization.
Tooling and quantity: flexible molds can have a low initial cost but limited life. Labor and cure time make this useful for short runs rather than a default for millions of pieces.
Geometry: good detail and some undercuts are possible with flexible tooling. Trapped air, cure shrinkage and heat from the reaction limit thin passages and thick pours. A closed hollow space still needs a removable or sacrificial core, or a different casting method.
Supporting detail: Addendum 40 — Public process reference.
Hand layup builds a fiber-reinforced composite against a tool
Hand layup builds a fiber-reinforced composite against a tool
In wet hand layup, reinforcing fabric or mat is placed against a mold, wetted with liquid resin and consolidated to reduce trapped air. Layers build thickness, then the resin cures.
Materials and products: usually a thermosetting polyester or epoxy matrix with glass or carbon fibers; boat shells and custom covers. These are composites in the Wood & Composites material family. Prepreg layup uses reinforcement already containing resin and is a related but different route.
Tooling and quantity: relatively simple one-sided molds support small runs and large custom parts. Manual work and cure time limit production rate.
Geometry: good for broad shells. The mold gives one face its finish; the other depends on the layup. Tight corners, inaccessible cavities and precise thickness on both faces are difficult. Fiber direction affects strength, so layer arrangement is part of the design.
Supporting detail: Addendum 41 — Public process reference.
Use geometry, material, quantity and tooling cost to narrow the process choice, then estimate cost per part and production rate.
Check geometry and material before comparing prices; Checklist
Check geometry and material before comparing prices
A low quoted price is irrelevant if the process cannot make the required shape or use the required material. Start with Plastics as Materials and the capability cards in Plastic Forming Processes.
Describe the geometry: hollow container, open sheet-like shell, constant cross-section or discrete solid part.
Choose a material type and candidate grade that meet the load, temperature and environment.
State the quantity, expected repeat orders and required delivery rate.
Check how the part leaves the tool: draft, undercuts and access to internal spaces.
Compare tooling, per-part cost, achievable detail and likely defects for the remaining processes.
Use part shape to build a short list; Practice
Use part shape to build a short list
Starting candidates, not exclusive rules
Need
Start with
Then ask
Many thin-walled hollow containers
Blow molding
Can the hot tube or preform stretch into this shape with an adequate wall?
A large hollow shell in a modest quantity
Rotational molding
Are the longer cycle and achievable detail acceptable?
An open tray or sheet-like cover
Thermoforming
Will the sheet thin too much, and can it release from the tool?
A long constant cross-section
Extrusion
Which end features or side holes would need later operations?
Many detailed discrete parts
Injection molding
Can walls stay reasonably uniform, and does quantity justify the mold?
Repeated thermoset parts or composite panels
Compression molding
Can the charge fill the matched tools before curing?
A few detailed resin parts
Casting
Will mold life, trapped air and cure time meet the need?
A custom fiber-reinforced shell
Hand layup
Is the labor acceptable, and can the reinforcement reach every region?
“Solid” does not mean “make every region thick.” An injection-molded housing is a discrete part, yet hollowing out bulky sections often improves it. Several processes can make a tank; size, quantity, resin and detail determine the better candidate.
Spread tooling cost over the number of acceptable parts; Practice
Spread tooling cost over the number of acceptable parts
A simple comparison is average cost per part = tooling cost / quantity + variable cost per part. Variable cost includes the costs that grow with production, such as material and processing time. Tooling cost is paid even if only a few parts are made.
Illustrative estimates, not supplier prices: suppose two processes can both meet a cover's specification. Route A costs $900 for tooling and $14 per part. Route B costs $18,000 for tooling and $2 per part.
Average cost per acceptable part, assuming no scrap or extra charges
Quantity
Route A
Route B
100
$900 / 100 + $14 = $23.00
$18,000 / 100 + $2 = $182.00
5,000
$900 / 5,000 + $14 = $14.18
$18,000 / 5,000 + $2 = $5.60
Supporting detail: Addendum 42 — Find the quantity where the two estimates are equal.
Cycle time and cavity count set the ideal production rate; Practice
Cycle time and cavity count set the ideal production rate
A cavity makes one part per cycle. With cycle time in seconds, ideal parts per hour = 3600 / cycle time × cavities.
For a 30-second cycle and two identical cavities: 3600 / 30 × 2 = 240 parts/h. That assumes uninterrupted operation and every part acceptable. Use the complete repeating cycle time, including opening and ejection; do not add overlapping cooling time twice.
Actual useful output is lower when setup, stoppages or rejects occur. More cavities may increase tooling cost and require a larger machine, so a higher ideal rate does not by itself settle the process choice.
Explain the choice with both a benefit and a limitation
Explain the choice with both a benefit and a limitation
A useful selection sounds like this: “For 300 large hollow PE garden reservoirs, investigate rotational molding because the shape fits and tooling can be economical at modest quantities. Confirm wall control and cycle time before committing.”
The quantity alone does not prove that choice. A narrow neck, precision sealing face, delivery deadline or different resin could change it. State the assumptions, identify a credible alternative, and compare the features that matter.
Supporting detail: Addendum 43 — Further process-selection reading.
Materials and Manufacturing Processes/Plastics
Cutting and Machining Plastics
Choose a separating process for the plastic and the feature, then control heat, chips and edge damage.
Choose the cut from the material and the feature
Choose the cut from the material and the feature
Separating removes material. A saw makes a blank, a drill makes a round hole, and a router or mill can make an outline, pocket or slot. Identify the resin and grade before choosing the process: two clear sheets can be acrylic and polycarbonate, with very different cutting behavior.
Process
Useful for
What controls the result
Sawing
Straight cuts or curved blanks on a band saw
Use a blade intended for the plastic and thickness. Teeth must cut without grabbing or packing the cut with chips; the finest tooth spacing is not always best.
Drilling
Holes through sheet or solid stock
Use suitable drill geometry, support the exit surface and provide chip clearance. Brittle acrylic can crack when the drill grabs at breakthrough.
Milling and routing
Accurate edges, slots and pockets
Sharp cutting edges, room for chips to escape and a supported workpiece reduce melting and chatter.
Laser cutting
Sheet profiles in an approved material
The resin, additives, thickness and laser wavelength matter. A glossy edge alone does not prove dimensional accuracy.
Hot-wire cutting
Contours in suitable thermoplastic foam
A heated wire softens a narrow path. This is not a general cutting method for solid plastic sheet or every foam formulation.
Heat builds up near the cut because plastics generally conduct heat poorly. Softened chips can stick to the tool or weld back onto the edge. The symptoms are smeared surfaces, strings of softened material and chips packed into the cutter.
Slowing the feed alone can make melting worse. Feed is how quickly the tool advances through the work; spindle speed is how quickly it turns. Too little advance per tooth lets the edge rub instead of taking a useful chip. Start with cutting data for the resin and tool, keep the tool sharp, and maintain chip clearance. Reducing excessive spindle speed may help, but feed, speed and cut depth must be considered together.
Deep holes need a planned way to clear chips. Coolants and cleaners must be compatible with the plastic; an unsuitable liquid can cause fine cracks called crazing. Use Feeds and Speeds for the relationships, not its metal cutting values as plastic settings.
Supporting detail: Addendum 44 — Why a slower cut can produce more heat.
Acrylic, PVC and polycarbonate behave differently under a laser
Acrylic, PVC and polycarbonate behave differently under a laser
Acrylic (PMMA) absorbs the infrared energy of a CO₂ laser. Concentrated heating removes material along the cut and can leave a smooth, glossy edge. That result depends on the sheet grade, thickness and process settings; it is not a promise for every clear plastic or every laser.
PVC is not a laser-cutting substitute for acrylic. Heating PVC can release hydrogen chloride; with moisture it forms hydrochloric acid, creating an exposure and corrosion concern. This is a chemical incompatibility, not simply a poor-looking edge.
Polycarbonate is often a poor choice for a clean CO₂-laser-cut sheet edge. It can yellow, char and leave a degraded edge instead of acrylic's clear finish. Specialized processes can cut some polycarbonate, so “polycarbonate cannot be laser processed” is too broad. Routing or sawing is often the better starting choice for a clear polycarbonate profile. Do not assign PVC's chlorine chemistry to polycarbonate.
Supporting detail: Addendum 45 — Manufacturer references and the limits of a material list.
Trim the molding excess without cutting into the part; Practice
Trim the molding excess without cutting into the part
A gate is the entry from a molding flow channel into the part cavity. Degating separates the part from that feed connection. Flash is a thin unwanted fin, often at a mold joint; trimming removes it. A burr is a raised edge left by cutting. These are different defects, even when the same trimming tool can remove them.
Support the part near the cut and leave the required contour intact. Cutting into the wall creates a notch that may start a crack. For batches, tumbling with suitable media can remove small burrs, but it can also round wanted edges or damage thin features. Inspect the dimensions and surface after the trial.
Match solvent cement, adhesive, welding or mechanical joints to the plastic pair, load and need for disassembly.
Start with both plastics and what the joint must do; Checklist
Start with both plastics and what the joint must do
Fabricating joins pieces into a useful assembly. Name both materials, then state the load, service temperature, appearance and whether the assembly must come apart. A leak-tight seam, a removable cover and a clear display corner need different joints.
These routes identify candidates. The actual grade, joint shape and service conditions decide whether a candidate works.
Identify the two resins and any coating or surface contamination.
State the load direction, environment and need for disassembly or sealing.
Check the joining product or process guidance for that material pair.
Make a representative trial joint and inspect it after full cure or cooling.
Solvent cement softens the surfaces; adhesive adds a bond layer
Solvent cement softens the surfaces; adhesive adds a bond layer
Solvent cementing uses a compatible liquid to soften or dissolve the surfaces so polymer chains can mix across the joint. As solvent leaves, the joint develops strength. It is chemical softening, not heat melting. Acrylic-to-acrylic is a common application; PVC and ABS also have specific cement systems. The cement must match the resin and fit of the joint.
Adhesives bond through a separate layer. Epoxies, cyanoacrylates and other formulations have different gap, flexibility and temperature limits. “Plastic glue” does not mean it bonds every plastic. Allow the specified cure time before loading; a joint that holds itself together may not have reached service strength.
Polyethylene (PE) and polypropylene (PP) resist many ordinary adhesives. Their low surface energy makes it difficult for an adhesive to spread into intimate contact, called wetting. Specialized adhesives or a controlled surface treatment can help; sanding alone is not a universal fix. See Chemicals and Safety Data Sheets for chemical handling.
Supporting detail: Addendum 46 — Why a clean-looking bond can peel off.
Welding needs compatible thermoplastics and a designed joint
Welding needs compatible thermoplastics and a designed joint
Plastic welding heats the joint region so compatible thermoplastics can fuse. Cooling while the joint is held in position completes the connection. Cured thermosets do not remelt into a comparable fusion weld. Even two thermoplastics are not automatically weld-compatible.
Method
How the joint forms
Typical reason to choose it
Hot-gas welding
A controlled stream of heated gas softens the joint faces and compatible filler rod.
Accessible seams or repairs in weldable sheet.
Extrusion welding
A tool supplies molten compatible filler while the base surfaces are preheated.
Larger seams needing more deposited material than a small rod weld.
Hot-plate welding
A heated tool softens mating faces; the tool withdraws and the faces are pressed together.
Parts with accessible matching joint faces.
Hot-wire or resistance-element welding
Electrical resistance heats a wire or element at a designed joint region. Tool arrangements differ.
A localized joint designed for that heating arrangement; not the foam-cutting process.
Ultrasonic welding
A horn applies rapid mechanical vibration under force, generating heat at the joint.
Repeated assembly of compatible molded parts with a suitable joint geometry.
Heat sealing
Heat and pressure fuse compatible film surfaces or their sealant layers.
Bag and packaging seams; not every multilayer film seals to itself.
Supporting detail: Addendum 47 — Why heat alone does not guarantee a strong or sealed weld.
Hot-melt adhesive is not a fusion weld
Hot-melt adhesive is not a fusion weld
A hot-melt adhesive is applied molten and usually gains handling strength as it cools. The adhesive melts; the two parts do not have to melt together. Choose the formulation for both surfaces, the available assembly time and the service temperature. An ordinary hot-melt joint may soften or creep under sustained load in warmth. Fast setting is not the same as suitability for structural service.
Use mechanical joints when access and disassembly matter; Practice
Use mechanical joints when access and disassembly matter
A snap fit bends a feature during assembly so it catches behind another feature. It needs room to flex, rounded transitions and a resin that tolerates the required strain. Some snap fits release repeatedly; others are intentionally difficult to undo.
Thread-forming screws for plastics create their mating thread in a designed hole. Repeated removal can wear plastic threads. A threaded insert supplies a metal thread; a heat-set insert is installed by locally softening a thermoplastic around it. Hole size, surrounding wall thickness and installation conditions come from the insert supplier. A metal insert cannot rescue an undersized plastic wall.
Through-bolts and suitable washers can spread the clamping load. Excessive tightening can crack brittle plastic; sustained load can cause creep, a gradual change in shape, and reduce clamping force. Allow for movement and thermal expansion rather than trapping a sheet tightly at every hole.
Compare two cases: a clear permanent acrylic corner is a candidate for compatible solvent cement; a PP cover that must be removed regularly is a candidate for screws and a suitable thread arrangement. An adhesive that works on the first pair tells you little about the second.
Supporting detail: Addendum 48 — Insert dimensions come from the chosen insert system.
Read an FDM part as deposited roads and layers, then choose orientation, walls, infill and supports for its job.
A slicer turns a solid model into deposited layers
A slicer turns a solid model into deposited layers
Material extrusion is the standard family in which material is selectively dispensed through a nozzle. This page covers thermoplastic filament printing, often called fused filament fabrication (FFF). Fused deposition modeling (FDM) is a registered trademark of Stratasys for an implementation of this mechanism. The machine feeds filament into a heated nozzle and lays down narrow roads of softened material that bond as the part builds. Relative motion between the nozzle and build plate advances the layers; the nozzle itself does not have to move upward on every printer.
A slicer converts the model into tool paths, including walls, internal fill and any temporary supports. Preview those paths before printing. An enclosed shape on a CAD screen does not tell you how its underside will be supported.
A section through a partly printed part. Walls, infill and supports are different tool paths. The large lines are illustrative, not a scale drawing.
Supporting detail: Addendum 49 — Where additive manufacturing fits the five course categories.
Layer height, walls and infill do different jobs
Layer height, walls and infill do different jobs
Layer height is the vertical increment between layers. A smaller height makes steps on sloping surfaces finer and usually adds print time. It does not make all small horizontal features printable: nozzle size, road width and motion accuracy also matter.
Walls or perimeters trace the boundary. Top and bottom layers close the part. Infill is the pattern inside those boundaries. More infill generally adds material and time, but strength also depends on walls, orientation, bonding and load direction. A 20% infill setting does not mean the entire part uses 20% of its solid volume, because the walls and skins remain.
Simple layer-count example: for a 24 mm height with every layer 0.20 mm thick, 24 ÷ 0.20 = 120 layers. Real slicers may use a different first-layer height or variable layers. Halving layer height roughly doubles the layer count, not necessarily the total print time.
Orient for the load as well as for fewer supports; Checklist
Orient for the load as well as for fewer supports
FDM parts are anisotropic: properties depend on direction. A load that pulls layers apart can expose a weaker bond than a load carried along continuous deposited roads. Avoid placing the main tensile load across layer interfaces when an orientation can carry it along the layers. This is a design starting point, not a strength rating.
An overhang extends beyond the layer below. A short bridge spans between supported ends. A long unsupported underside may need temporary support material. Support contacts can leave marks, so keep them away from critical visible or mating surfaces where possible. There is no universal overhang angle that works for all materials and settings.
For a rectangular test bar pulled along its length, laying its length in the build plane usually gives a better starting orientation than standing it upright and pulling across stacked layers. A bracket may have several important load directions; choose a compromise or change the design, then test it.
Mark the main load direction and critical fit surfaces on the model.
Compare orientations for layer direction, build-plate contact and unsupported undersides.
Preview walls, infill and supports one layer at a time.
Check that support can actually be removed from each enclosed space.
Choose filament for service conditions and printer capability
Choose filament for service conditions and printer capability
Filament
Useful starting point
Check before choosing
PLA
Stiff models and easy-to-print prototypes
Heat exposure and impact requirements; a neat print is not automatically suitable for a warm enclosure.
PETG
Tougher functional parts with useful layer bonding
Stringing, moisture and support-removal behavior for the grade.
ABS / ASA
Applications needing greater heat resistance than ordinary PLA; ASA is often chosen for outdoor exposure
Warping control, equipment capability and processing requirements.
TPU
Flexible parts
Hardness grade and whether the feed system can handle flexible filament.
Nylon (polyamide)
Tough engineering parts
Moisture control, dimensional change and the required printing conditions.
PVA is used as a water-soluble support material in compatible multi-material systems; it is not a universal companion for every filament. Use the exact filament manufacturer's settings and the printer's limits. Consult Equipment Operating Procedure and Chemicals and Safety Data Sheets for process controls.
Supporting detail: Addendum 50 — Material guidance is grade-specific.
Estimate mass from deposited volume, not infill alone; Practice
Estimate mass from deposited volume, not infill alone
Mass = deposited volume × density. If a simplified model has 8 cm³ of solid walls and skins plus a 32 cm³ interior at 25% infill, its estimated deposited volume is 8 + (32 × 0.25) = 16 cm³. At an assumed density of 1.24 g/cm³, that is 19.84 g. Supports, brims and purge material add more.
This estimate treats infill percentage as a volume fraction of the interior. A slicer estimates the actual paths more closely. Time also includes travel, acceleration, heating and cooling constraints; volume alone does not give an exact printing duration.
Separate property changes from surface treatments, and match annealing, smoothing and coatings to the exact plastic.
Conditioning changes properties; finishing changes the surface
Conditioning changes properties; finishing changes the surface
Conditioning changes the material's state or properties: relieving internal stress, developing a thermoset cure, or controlling absorbed moisture. Finishing changes the surface for appearance, protection or function. A part can need both. Removing a support is Separating; sanding the resulting surface is Finishing.
Start with the resin, dimensions and service requirement. A glossy surface does not prove that a part is strong, properly cured or dimensionally correct.
Annealing relieves stress, but can change dimensions
Annealing relieves stress, but can change dimensions
Annealing uses a controlled heating, holding and cooling schedule. In acrylic it can reduce stress left by machining, bending or polishing. It is not a general instruction to heat near molding temperature. Use the resin supplier's schedule for the grade and thickness, including support of the part during treatment.
Printed PLA can also be annealed. Depending on its formulation and thermal history, heating can allow more crystalline order and improve heat resistance. Shrinkage, expansion in another direction or warping can spoil a fit. Measure before and after; do not assume every strength property improves.
Supporting detail: Addendum 51 — Stress relief and crystallinity are different changes.
Curing creates a network; drying removes moisture
Curing creates a network; drying removes moisture
A thermoset cure is a chemical reaction that builds links between polymer chains. Resin and hardener, heat or light may initiate the reaction, depending on the system. Correct proportions, time and temperature matter. A prescribed post-cure can develop properties further; an already cured thermoset will not simply remelt like a thermoplastic.
Drying moisture-sensitive filament addresses a different problem. Moisture can affect extrusion and part quality, but drying does not replace annealing or cure. Use a drying schedule intended for the material; excessive heat can deform filament or its spool.
Remove scratches progressively before adding gloss or paint
Remove scratches progressively before adding gloss or paint
Sanding replaces a coarse scratch pattern with progressively finer scratches. Start with the finest abrasive that will remove the defect efficiently. Within the same grit system, a larger number generally means a finer abrasive. A sequence such as P240 → P320 → P400 → P600 illustrates progression; it is not a required recipe for every plastic or coating.
Remove the previous scratch pattern before moving on and clean away abrasive residue between stages. Wet sanding with suitable waterproof abrasive can reduce loading and heat where the material and equipment permit it. Keep corners and fit surfaces from rounding over. Paint may need a controlled scuffed surface rather than a polished one; follow its preparation specification.
Tumbling can finish many parts together, but media and time affect edge rounding and small features. Buffing can improve gloss, but excessive heat or pressure can smear the surface. Check a representative sample rather than equating more polishing with a better part.
Flame and solvent smoothing are material-specific processes
Flame and solvent smoothing are material-specific processes
Flame polishing can smooth suitable acrylic edges by briefly softening the surface. It can also round edges and introduce stress. It is not a general treatment for clear plastics: polycarbonate is not interchangeable with acrylic, and a process must be validated for its exact grade. A clear edge is not necessarily an optically accurate or low-stress edge.
Solvent or vapor smoothing softens a compatible polymer's surface chemically. Acetone smoothing is associated with ABS and ASA; do not transfer that recipe to PLA or PETG. Smoothing can erase fine lettering, change dimensions and alter mechanical performance. It does not guarantee that weak layer bonds inside a print have been repaired.
Supporting detail: Addendum 53 — Why a clear surface can crack later.
Coatings need adhesion as well as the right appearance; Practice
Coatings need adhesion as well as the right appearance
For paint, remove contamination with a compatible cleaner, prepare the surface as specified and use a primer or adhesion promoter when the coating system calls for one. PE and PP often need special preparation or products because of low surface energy. A primer is not automatically compatible with every plastic. Trial the complete system, including cure, on a representative sample.
Dip coating deposits a liquid film as the part is withdrawn, followed by drying or curing as the formulation requires. Withdrawal rate and liquid properties affect thickness. Powder coating plastics requires a suitable way to attract or deposit the powder and a cure that the part can withstand; an insulating plastic does not become conductive merely because a grounding wire touches it.
Electroplating needs a conductive surface. Plastics therefore require preparation and a conductive layer before electroplating. Decorative options also include printing, decals, in-mold labels and dyes for receptive polymers. Choose them for the required abrasion, outdoor exposure and chemical resistance; decoration is not automatically protection.
Supporting detail: Addendum 54 — Powder coating needs a complete substrate and cure system.
Read tree structure, distinguish botanical groups, and choose species for their properties rather than their names.
Wood belongs to the Wood & Composites family
Wood belongs to the Wood & Composites family
Wood is a cellular material whose properties depend on direction. Long cells run mainly along the trunk; their arrangement helps explain why a board carries loads and splits differently along and across its grain.
In the material-family model, wood belongs to Wood & Composites. Engineered wood products combine veneers, strands, particles, or fibers with binders. These products are why composites share this family. See Engineered Wood Products for the product choices; the material families and manufacturing process categories are foundation topics.
Supporting detail: Addendum 55 — What makes the cell walls work together?.
Read a trunk from bark to heartwood
Read a trunk from bark to heartwood
Bark
Outer bark protects the tree. Inner bark carries sugars made by the leaves.
Cambium
A thin growing layer produces new wood toward the inside and new inner bark toward the outside.
Sapwood
The outer wood conducts water and contains living storage cells. Many of its conducting cells are already dead at maturity.
Heartwood
Older inner wood no longer conducts water. Deposits can change its color and decay resistance; heartwood is not automatically stronger or decay-resistant in every species.
Pith and rays
The pith marks the central stem tissue. Rays run radially across the wood and contribute to storage and transport across the trunk.
A growth ring records a growth cycle. In many temperate trees, earlywood develops earlier in the season and latewood later. Their cells differ in size and wall thickness, creating visible bands. Ring contrast varies by species; ring width alone is not a strength grade.
Hardwood and softwood describe the tree, not its hardness; Practice
Hardwood and softwood describe the tree, not its hardness
Hardwoods come from angiosperm trees; softwoods come from gymnosperm trees, commonly conifers. Leaf shedding is not the defining test: some hardwood trees are evergreen, and some conifers shed their needles.
Balsa is a very soft hardwood. Southern yellow pine is a softwood but can be much harder than balsa. Ask about the species and the property you need, rather than treating the category name as a test result.
Supporting detail: Addendum 56 — How the cell structure differs.
Connect grain orientation and moisture changes to board movement, defects, and design choices.
Follow the grain through the face, edge, and end
Follow the grain through the face, edge, and end
Grain describes the direction of wood cells. Figure is the visible pattern created by growth structure and the way the wood is cut. A board's broad surface is its face, its narrow long surface is its edge, and its cut end exposes end grain. Face and edge grain usually run generally along the board; they are not separate botanical structures.
Wood is generally stronger in tension along the grain than across it. A short projection with grain running across its narrow base can split off even if the rest of the part is thick. Knots divert nearby grain, and sloping or interlocked grain makes a board less predictable.
During machining, a cutting edge can lift fibers ahead of the cut and tear them out. Grain direction helps predict that result, but does not replace the machine's operating procedure. See Machine Hazards and Housekeeping and Equipment Operating Procedure for safety; wood separating and finishing are later topics.
Sawing orientation changes figure and movement
Sawing orientation changes figure and movement
Read the growth rings on the end of a board. Plain-sawn boards have rings more nearly parallel to the broad face and often show cathedral-shaped face figure. Quarter-sawn boards have rings more nearly perpendicular to the face; their width follows the radial direction more closely. Rift-sawn boards have an intermediate, oblique ring angle and commonly show straight face grain.
Quarter-sawn oak can expose conspicuous ray fleck. Rift-sawn oak is often selected for straight grain with less prominent fleck. Trade descriptions and angle boundaries vary, so inspect the end grain as well as the sales label. The diagram shows selected orientations, not a mill's complete cutting plan.
Moisture content uses oven-dry wood mass as its reference
Moisture content uses oven-dry wood mass as its reference
MC (%) = (wet mass − oven-dry mass) / oven-dry mass × 100. A sample weighing 150 g before drying and 100 g after oven drying has 50% MC. MC can exceed 100% because the reference is dry wood mass, not the original wet mass.
Water occupies cell cavities and is also held in cell walls. At the fiber saturation point, the walls are saturated while the cavities contain no free liquid water. Below this region, loss of water from the cell walls causes appreciable shrinkage. It is not one exact threshold for every species and condition.
Equilibrium moisture content (EMC) is the moisture content wood approaches in a particular surrounding humidity and temperature. A board can be dry today and absorb moisture later.
Green
Freshly cut or unseasoned; moisture varies greatly.
Air-dried
Dried by surrounding air; the achievable condition depends on the climate and storage.
Kiln-dried
Dried in a controlled chamber. This is a drying history, not a promise that the board will never move or that every kiln-dried product has the same MC.
Choose and acclimate material for its intended service environment. Use measurements to judge readiness; a fixed number of days cannot guarantee equilibrium for every thickness and starting condition.
Most movement is across the grain; Interactive
Most movement is across the grain
For normal straight-grained wood, shrinkage is usually greatest tangentially (along growth rings), smaller radially (across rings), and much smaller longitudinally (along the cells). Swelling reverses the moisture-loss trend. Actual amounts depend on species, grain orientation, and the moisture interval.
Do not apply a green-to-oven-dry shrinkage percentage directly to a small seasonal humidity change. A movement estimate needs a species-specific coefficient, board orientation, starting MC, and expected service MC. Reaction wood and juvenile wood can also depart from ordinary longitudinal behavior.
Estimate movement using starting dimension × coefficient × (final MC − starting MC), with both MC values within 6–14%. The attachment experiment below separates total width change from travel at a particular point.
Wood movement and attachment clearance — both moisture contents must be 6–14%.
Change = starting dimension × coefficient × (final MC − starting MC), with MC entered as a percentage (8, not 0.08). Negative means shrinkage; positive means swelling. Use the tangential coefficient CT for the width of a flat-sawn board or when the ring orientation is unknown, and the radial coefficient CR for the width of a quarter-sawn board or the thickness of a flat-sawn one.
Worked example: a flat-sawn white fir board 9.15 in wide at 8% MC, CT = 0.00245, reaching 11% MC: 9.15 × 0.00245 × (11 − 8) = 0.0672525 in wider, about 9.2173 in final width. The exact conversion starts at 232.41 mm and ends at about 234.118 mm. The Handbook's separately rounded 232 mm example ends at about 233.705 mm.
Predict: with one ideal fixed reference on a stationary support, does center fixing make the right edge move half as far, the same distance, or not at all, compared with fixing the left edge?
Same total width change, different edge travel: 8% to 11% MC
Fixed reference
Left edge travel
Right edge travel
Center
0.0336 in outward
0.0336 in outward
Left edge
0 (fixed)
0.0673 in outward
For uniform free strain, signed point displacement = (signed distance from the fixed reference ÷ installed width) × total width change. Center fixing halves the edge travel, not the total width change. A point closer to the reference travels less.
Compare available travel in each direction from the installed position. With 0.040 in outward travel, center-fixed edges remain inside the travel window, while the opposite edge of the left-edge-fixed board exceeds it. Drying reverses the movement: 8% to 6% MC gives 0.0224 in inward travel at each center-fixed edge, exceeding a separate 0.020 in inward allowance. Enough travel in one direction does not supply travel in the other.
Each estimate starts from the installed dimension and MC. Edge points are geometric tracking points, not a fastening layout. The support is stationary, with one ideal fixed reference and otherwise free uniform width change; friction, warp, strength, restraint stress and cracking are not calculated. Exceeding a travel window does not predict what the restrained board will do. A result within the window does not approve a joint.
Commercial lumber is rarely perfectly flat- or quarter-sawn, so this method can overestimate width shrinkage and underestimate thickness shrinkage. Board properties and ring angles vary. These are approximate estimates; no correction or safety factor is added. Outside 6–14% MC a different method applies.
Name the distortion before deciding what to do; Practice
Name the distortion before deciding what to do
Defects described by shape
Defect
What you see
Cup
Curvature across the width: the face resembles a shallow trough.
Bow
Curvature along the length, out of the broad face's plane.
Crook
Curvature along the length within the face's plane; the edge wanders sideways.
Twist
The corners no longer lie in a common plane.
Check / split
A separation along the grain. A check may be confined to a surface or end; a split extends through the piece.
Unequal shrinkage, uneven moisture, and irregular grain can contribute to warp. Drying stresses can open checks and splits. A stain is a color change, not automatically proof of lost strength; decay is a different concern.
Allow solid wood to change width; Checklist; Practice
Allow solid wood to change width
A solid-wood tabletop needs room to expand and contract across its grain. Suitable slotted attachments let it move relative to a supporting frame. A panel held in grooves needs clearance rather than rigid restraint across its full width. Details depend on the joint and expected movement.
Choose the fixed reference deliberately, then check travel from each attachment's installed position in both moisture directions. Slot length alone does not give clear travel: the fastener occupies space, and its starting position divides the available movement. The experiment above uses clear travel directly rather than inferring a hardware size.
Do not assume that a finish locks moisture out. It can slow moisture exchange, but does not eliminate seasonal movement. Plywood often solves a panel-stability problem better than simply making a solid board thicker.
Identify the grain direction and width that can move.
Check moisture against the intended service environment.
Inspect for warp, splits, and grain interruptions before laying out parts.
Check that attachments allow the expected movement.
Wood conditioning and fabricating cover drying and joint-making in more detail; Engineered Wood Products compares alternatives to solid lumber.
Separate sales size from measured size and calculate board footage using an explicit dimension convention.
Nominal size is a name; actual size is what fits; Practice
Nominal size is a name; actual size is what fits
A nominal lumber size identifies a product category. Dry, surfaced construction lumber sold as a 2 × 4 commonly measures 1-1/2 × 3-1/2 in in cross-section. Rough, green, specialty, and reclaimed stock can differ. Measure the piece when fit matters.
Drying and surfacing help explain the difference, but nominal names are not a universal subtraction rule. Do not assume that removing the same amount from every nominal size will give its actual dimensions.
Quarter thickness and surfacing describe different things
Quarter thickness and surfacing describe different things
Hardwood thickness is often named in quarter-inch increments before final surfacing: 4/4 means nominal one-inch stock and 8/4 means nominal two-inch stock. Neither guarantees that much finished thickness. Drying, flattening, and planing reduce the usable material.
Rough
Sawn surfaces remain; allow material for flattening and sizing.
S2S
Surfaced on two sides, normally the two broad faces. Do not assume the edges are straight or ready for a joint.
S4S
Surfaced on all four long sides: both faces and both edges. Ends are not included in the four.
Ask for the supplied thickness, width, length, moisture condition, grade, and surfacing. A thickness label alone is not a complete purchase specification.
A board foot is volume, not length
A board foot is volume, not length
One board foot (BF) is the volume of a piece 1 in × 12 in × 12 in: 144 cubic inches. With thickness and width in inches and length in feet:
If all three dimensions are in inches, divide by 144 instead. Multiply by the number of identical boards only after finding the volume of one.
Supporting detail: Addendum 59 — Why the mixed-unit formula divides by 12.
State the measuring convention. A physical-volume calculation uses actual dimensions. A sales tally may use nominal thickness or other trade rules and may round individual board measurements. Ask the seller; do not replace a quoted tally basis with finished dimensions without saying so. The examples here explicitly specify their basis and use unrounded arithmetic until the final answer.
Keep purchase tally and finished volume separate; Interactive; Practice
Keep purchase tally and finished volume separate
Suppose a seller specifies a tally using nominal 1 in thickness, measured 7 in width, and 9 ft length. The tally is 1 × 7 × 9 / 12 = 5.25 BF.
If that board finishes at 3/4 in thick with the same width and length, its physical volume is 0.75 × 7 × 9 / 12 = 3.9375 BF, or 3.94 BF to two decimals. These answers describe different quantities. The finished volume does not change the stated sales agreement.
A board tally is not a finished-parts yield. Allow for saw cuts, defects, flattening, trimming, and the layout of the parts. Appearance grades and structural grades answer different questions; an attractive board is not automatically suitable for a load-bearing member.
Build a list of boards below to compare the sales tally with actual volume, calculate cost, and estimate a material allowance.
Say which allowance you mean. This calculator treats the allowance as the share of the material you buy that will not end up in parts: BF to buy = needed BF ÷ (1 − allowance), so a 20% allowance means buying 1.25 times what you need. Many shop guides instead say “add 20%” to what you need (× 1.20), which is a different definition and buys less. Both are used; check which one a source or an instructor means before you compare numbers.
Compare veneers, strands, particles, fibers, and laminations to choose a wood product for its intended use.
Engineered wood changes the arrangement of the wood
Engineered wood changes the arrangement of the wood
Engineered products combine wood pieces with binders to make sheets or members that a single log could not supply as consistently. They belong to Wood & Composites: the wood supplies much of the structure, while the binder holds the selected arrangement together.
Engineering redistributes natural variability; it does not make all products equally strong, waterproof, or free of manufacturing defects. Select the product grade, thickness, orientation, exposure suitability, and fastening details for the job.
Plywood cross-laminates veneers to restrain movement
Plywood cross-laminates veneers to restrain movement
A veneer is a thin sheet of wood. In plywood, adjacent veneer layers commonly have grain at right angles. Each layer restrains the cross-grain movement of neighboring layers, making the panel more stable in its plane than a comparable wide solid-wood board.
Conventional plywood commonly has an odd number of plies in a balanced layup, with matching face-grain directions. Odd ply count is not a universal rule for every panel construction. The grain direction of the faces still matters to panel stiffness and strength; cross-lamination does not mean equal performance in every direction.
Plywood serves cabinet boxes, furniture panels, sheathing, and subfloors when the appropriate product is selected. Face appearance, core voids, bond durability, and panel rating vary. A decorative face veneer does not establish a structural rating.
Choose the sheet by its structure and service conditions; Practice
Choose the sheet by its structure and service conditions
Sheet goods: useful differences
Product
Structure and strengths
Limits and typical uses
OSB: oriented strand board
Wood strands bonded in layers with deliberate orientation. Structural grades provide useful panel strength and stiffness.
Common in wall, roof, and floor sheathing. Follow the marked strength direction and rating. Edges can swell when wetted; it is not a decorative substitute for every plywood face.
MDF: medium-density fiberboard
Fine wood fibers and resin produce a smooth surface without solid wood's visible grain pattern. Well suited to painted profiles.
Common in interior cabinet doors and trim. Heavy; ordinary grades swell with moisture. Edge fastening needs suitable hardware and preparation. Moisture-resistant grades are not automatically waterproof.
Particleboard
Small wood particles bonded into an economical, comparatively uniform panel; useful as a substrate under a decorative surface.
Common in interior furniture and laminate countertops. Ordinary grades are moisture-sensitive, edges are vulnerable, and fastener holding and shelf deflection need attention.
Painting a moisture-sensitive board does not turn it into a product rated for prolonged wet exposure. For wood dust and product-handling hazards, use Personal Protective Equipment and Chemicals and Safety Data Sheets rather than inferring precautions from a product's name.
Glulam bonds lumber laminations with their grain generally parallel to the member's length. It is used for structural beams and columns, including large members and curved forms.
LVL (laminated veneer lumber) bonds thin veneers with grain predominantly along the member. It is part of the structural composite lumber group and is commonly used for beams and headers over openings. It is not simply thick plywood: its layup favors lengthwise performance.
Use the manufacturer's design information for a particular structural product. Product names alone do not give allowable loads, spans, or permission to cut holes. Lamination and bending methods belong to the later wood forming and fabricating topics.
Match teeth to grain direction, leave room for chips, and include the saw's kerf in every cutting layout.
Teeth remove chips; the kerf is the wood they remove
Teeth remove chips; the kerf is the wood they remove
Sawing is a Separating process: each tooth removes a small chip, and successive teeth make a slot. The slot's width is the kerf. The space ahead of a tooth, called the gullet, carries chips out of the cut.
Many steel saw teeth have set: teeth bend slightly to alternating sides so the cut is wider than the blade body. Carbide-tipped circular blades commonly get that clearance from tips wider than the steel plate instead. Set and kerf are related, but they are not the same measurement.
A rip cut runs along the grain, usually to reduce a board's width. A crosscut runs across the grain, usually to reduce its length. Describe the cut relative to the grain, not just as a long or short cut.
Ripping teeth commonly have a flat, chisel-like cutting edge. Crosscut teeth commonly have alternating bevels that score and sever fibers at the sides of the cut. These are useful patterns, not universal rules: combination and specialty blades use other arrangements.
For circular blades of the same diameter, more teeth generally share the work into smaller bites at the same feed and rotational speed. That can improve a crosscut surface, but leaves less space for chips. Thick ripping cuts often benefit from fewer teeth and larger gullets. “Thicker wood needs more teeth” is not a general rule.
Band and reciprocating blades commonly specify teeth per inch (TPI). Tooth spacing must suit the thickness engaged in the cut. A coarse blade has more chip space; a finer blade can suit thinner stock and finer work. Blade width also matters on a band saw: a narrower blade can follow a tighter curve.
Hook angle describes the tooth face's lean relative to a radial line on a circular blade. More positive hook generally gives a more aggressive bite; low or negative hook is less aggressive. Machine type and the blade maker's intended application matter along with the desired finish. A ripping blade is not automatically appropriate on a miter saw.
See Feeds and Speeds for the relationship between tooth engagement, feed and cutting speed; metal-cutting settings do not transfer directly to wood.
Supporting detail: Addendum 63 — Blade terminology reference.
Count cuts before calculating strip yield; Practice
Count cuts before calculating strip yield
Start with the usable width after any edge preparation. Let W be usable board width, s the required strip width and k the kerf, all in the same units. These ideal layouts assume straight cuts, exact dimensions and no extra finishing allowance.
One cut per strip, leaving an offcut:used width = n(s + k). The maximum whole number is floor(W / (s + k)); “floor” means round down. For a 12 in board, 3 in strips and a 1/8 in kerf, floor(12 / 3.125) = 3 strips. Three cuts use 9.375 in, leaving 2.625 in. Four strips alone use 12 in, leaving no room for the cuts.
All final pieces use both original outside edges:W = ns + (n − 1)k for an exact partition. There are only n − 1 cuts between n pieces. If a layout leaves an extra offcut to separate, count that extra cut too. Draw the layout before choosing a formula.
Real layouts also allow for defects, edge trimming and later machining. Kerf is material removed, not useful strip width.
Start with the required cut, surface or hole, then match the machine and cutter to that result.
Choose the required geometry before choosing the machine; Checklist
Choose the required geometry before choosing the machine
A machine name does not describe a finished part. First state the result: a straight edge, a curved outline, a flat face, a hole or a round profile. Then consider the workpiece dimensions, accuracy, surface quality and available tooling. The machines below remove material and belong to Separating.
This is a selection guide, not an operating procedure. Machine-specific use belongs with Machine Hazards and Housekeeping and Equipment Operating Procedure. Grain and moisture are covered in the wood-as-a-material topic; the operation selected here depends on those properties.
Describe the surface or cut that must exist when the operation is complete.
Identify which existing face or edge can locate the workpiece.
Check machine capacity and whether the cutter can reach the feature.
Decide whether the cut is final size or leaves material for another operation.
Match the cut to a suitable starting machine; Practice
Match the cut to a suitable starting machine
Common choices; capacity and tooling can change the selection
Required result
Starting choice
What distinguishes it
Straight rip to width
Table saw
The fence locates a straight reference edge for a parallel cut.
Square crosscut or miter
Miter saw; table saw with crosscut sled or miter gauge
A miter is an angled cut across the width. Crosscut capacity limits the workpiece size.
Dado across a face
Router; table saw with compatible dado tooling
A dado is a flat-bottomed channel across the grain. Not every table saw accepts a dado set.
Curved outside outline
Band saw or jig saw
A band saw uses a continuous loop; a jig saw uses a short reciprocating blade.
Resaw into thinner boards
Band saw
The cut passes through the board's width to divide its thickness. Resaw capacity and blade selection matter.
Enclosed interior opening
Jig saw or scroll saw
A starter hole gives blade access without a cut from the outside edge. A scroll saw suits fine, intricate work; its blade can be threaded through the hole.
Router bits make profiles and channels; templates repeat shapes; Practice
Router bits make profiles and channels; templates repeat shapes
A router spins a router bit. Straight or spiral bits make channels and pockets; roundover and chamfer bits change an edge's profile. A bearing-guided bit or guide bushing can follow a template, which is a pattern used to reproduce an outline.
Routers may be handheld, mounted in a table or moved by a CNC machine. A shaper commonly carries profile cutters on a table-mounted spindle. Both shape wood, but their cutters and mounting systems are not interchangeable merely because the resulting profile looks similar.
Supporting detail: Addendum 64 — Why “router bit” is more useful than “end mill” here.
Spindle and faceplate turning put grain differently relative to the axis
Spindle and faceplate turning put grain differently relative to the axis
In typical spindle turning, grain runs mainly parallel to the rotation axis, as in a handle or table leg. In typical faceplate or bowl turning, grain runs mainly across the axis, as in a bowl blank. Faceplates and chucks are workholding methods; the name alone does not guarantee the grain orientation.
Turning removes material to make circular features. It does not bend the wood. Lathe Operations explains metal-lathe operations as a separate topic; wood turning has different tools and workholding practices.
Choose a drill bit for the hole's bottom, edge and diameter; Practice
Choose a drill bit for the hole's bottom, edge and diameter
Common wood-hole tools
Bit
Useful result
Limit to remember
Twist
General holes in a range of diameters
The usual point leaves a conical bottom in a blind hole.
Brad-point
Accurately located holes with clean entry edges in wood
The center point projects beyond the cutting lips.
Forstner
Clean-sided blind recess with a largely flat bottom
Most leave a small center-point mark; “flat” does not mean perfectly featureless.
Spade
Economical larger holes where finish is less critical
Usually leaves a center-point recess and a rougher result.
Hole saw
Large through-hole by cutting around a core
Leaves a plug; it does not clear a flat-bottomed pocket.
A drill press improves control of axis and depth; it does not make every bit suitable for every hole. Cutter geometry, workpiece support and setup still affect accuracy.
Establish one flat face and one square edge before making the opposite surfaces parallel and cutting to length.
A jointer establishes flatness; a planer establishes thickness
A jointer establishes flatness; a planer establishes thickness
Stock is the material a part starts from. Rough lumber may have uneven surfaces or warp. A jointer removes material to establish a flat face. With that face as a reference against a square fence, it can establish a straight edge at 90° to the face.
A thickness planer cuts the upper face relative to the face supported by its bed. With a flat reference face down, it makes the opposite face parallel and brings the board to thickness. Jointing both faces separately does not ensure they are parallel.
Supporting detail: Addendum 65 — Why a planer alone can preserve a bow.
Build reference surfaces in order: face, edge, thickness, width, length; Practice
Build reference surfaces in order: face, edge, thickness, width, length
This is the geometry sequence for preparing rough stock. It assumes enough material remains for the finished dimensions and that the stock fits the equipment. It is not a machine setup guide; use Equipment Operating Procedure and Machine Hazards and Housekeeping for operation.
Face-joint: establish a flat face and mark it as the reference.
Edge-joint: use the reference face to establish one straight edge square to it.
Plane: place the reference face against the planer bed and bring the opposite face parallel to it at the required thickness.
Rip: use the straight reference edge to locate the cut; make the opposite edge parallel at the required width.
Crosscut: establish a square end, then cut the other end to the required length.
Any preliminary breakdown into shorter, oversized blanks comes before final sizing. Leave allowance for the later cuts; an early rough crosscut is not the final crosscut in this sequence.
Try the order on a warped board: what each machine removes or copies; Interactive
Try the order on a warped board: what each machine removes or copies
Pick a board with cup, bow, twist or crook, as defined in Grain and Moisture Movement. Choose the next operation, predict the result, then check it with a straightedge, winding sticks and a square. Try the planer first, then the reference order, and compare. This is reference-surface geometry, not machine operation: see Jointer, Table Saw and Equipment Operating Procedure before using the machines.
Square a warped board. With JavaScript, this card is an interactive board you can machine one operation at a time: pick a cup, bow, twist or crook, predict what the jointer, planer or table saw will do, and check the result with a straightedge, winding sticks and a square. The figures below come from the same model.
The reference order on four warped boards
Each strip starts with a rough board (warp exaggerated to be visible) and applies face-joint, edge-joint, plane, rip and crosscut. Every later step uses a surface an earlier step made true.
Cup board, Joint face, Joint edge, Plane, Rip, Crosscut. Final: face A 0.0 mm out of flat, thickness 19.0 mm, edge A 0.0° off square.Bow board, Joint face, Joint edge, Plane, Rip, Crosscut. Final: face A 0.0 mm out of flat, thickness 19.0 mm, edge A 0.0° off square.Twist board, Joint face, Joint edge, Plane, Rip, Crosscut. Final: face A 0.0 mm out of flat, thickness 19.0 mm, edge A 0.0° off square.Crook board, Joint face, Joint edge, Plane, Rip, Crosscut. Final: face A 0.0 mm out of flat, thickness 19.0 mm, edge A 0.0° off square.
Planer first: thickness becomes even, the cup stays
Cup board, Plane, Joint face, Joint edge, Plane, Rip, Crosscut. Final: face A 0.0 mm out of flat, thickness 13.1–19.0 mm, edge A 0.0° off square.
Worked example (cupped board). The rough board’s face A is 6.2 mm out of flat. In the flexible-board example the planer presses it flat, cuts the top parallel to the pressed underside, and releases it: thickness becomes 19.0 mm, but face A is still 6.2 mm out of flat and face B now copies the cup (6.1 mm). Flattening face A afterwards leaves the board 13.1–19.0 mm thick, short of 19 mm. In the reference order the same board finishes at 19.0 × 110.0 × 520.0 mm with every check at zero within the model’s tolerance.
Cup board: what each step leaves (model mm). Planer: flexible board pressed flat by the rollers.
Order
After
Face A out of flat
Face B out of flat
Thickness
Edge A off square
Planer first
Rough board
6.2
6.1
36.0
6.9°
Planer: face A on the bed, plane to 19 mm
6.2
6.1
19.0
6.9°
Jointer: flatten face A
0.0
6.1
12.9–19.0
0.8°
Jointer: straighten edge A against the fence
0.0
6.1
12.9–19.0
0.0°
Planer: face A on the bed, plane to 19 mm
0.0
6.1
12.9–19.0
0.0°
Table saw: rip to 110 mm, edge A on the fence
0.0
3.4
13.1–19.0
0.0°
Crosscut: square both ends to 520 mm
0.0
3.4
13.1–19.0
0.0°
Reference order
Rough board
6.2
6.1
36.0
6.9°
Jointer: flatten face A
0.0
6.1
29.9–36.0
0.8°
Jointer: straighten edge A against the fence
0.0
6.0
29.9–36.0
0.0°
Planer: face A on the bed, plane to 19 mm
0.0
0.0
19.0
0.0°
Table saw: rip to 110 mm, edge A on the fence
0.0
0.0
19.0
0.0°
Crosscut: square both ends to 520 mm
0.0
0.0
19.0
0.0°
Edge before face. On the twisted board, jointing edge A first and face A second leaves edge A 1.9° out of square: where the twisted face touched the fence, its local angle set the edge angle. Flatten the face first, then use it against the fence.
What the model assumes
Geometry only, in millimetres. The board is a grid of points on its faces, edges and ends. Every cut is a plane or a surface built from straight lines, and a point outside the cut slides inward along the board until it reaches the cut, so no step can add material.
Jointer face: an ideal long, flat table. The board rests on its lowest points; the cut stays parallel to that resting plane and passes continue until the deepest hollow is reached. The pass count shown is an illustrative step, not a depth-of-cut recommendation.
Jointer edge and table-saw rip: the edge rests on its outermost points along a long table or fence, so the cut is straight along the length. The face touching the fence or table beside the cutter sets the edge angle, so a flat face gives a square edge and a twisted face does not.
Planer, flexible-board example: feed-roller pressure is assumed to bend the board until its overall curve lies on the bed; the top is cut parallel to that pressed underside and the warp returns on release. A stiffer board, or one shimmed on a flat sled, can instead keep its resting attitude; switch the planer to the rigid case to compare. Neither case is a rule for every board or planer.
Crosscut: each end is cut perpendicular to face A and edge A near that end, first end just to clean up, second end at the finished length.
Warp amounts (cup 6 mm, bow 14 mm, twist 12 mm, crook 16 mm on a 640 × 150 × 36 mm blank) are deliberately large illustrative values, not measured boards. Machine setup, feed, guards, snipe, tearout, kickback and moisture movement are outside this model.
Check geometry instead of counting machine passes; Checklist
Check geometry instead of counting machine passes
One pass is not proof that a surface is ready. The result of each stage is the reference for the next. Flatness means a surface lies in a plane; parallel faces maintain a constant separation; square surfaces meet at 90°.
Check the reference face for flatness with a straightedge and for twist with winding sticks, a matched pair of sighting bars.
Check the reference edge for straightness and squareness to the face.
Measure thickness at several positions after planing.
Check width, parallel edges, end squareness and final length.
Recheck dimensions and geometry if material removal releases stresses and the board moves.
Stop and reconsider the intended dimensions if flattening would make the board too thin or too narrow. No sequence can recover material already removed. Use How Saws Cut Wood to account for kerf in the width and length layout.
Materials and Manufacturing Processes/Wood
Bending and Laminating Wood
Compare steam bending, kerf bending, bent lamination and veneering by what changes shape and what holds the result.
Separate the bending step from the cutting and bonding steps
Separate the bending step from the cutting and bonding steps
Bending changes the shape of wood and belongs to Forming. A complete route can use several of the five process categories: cutting thin strips or kerfs is Separating; bonding layers is Fabricating. Veneering bonds a thin wood facing to a supporting base, so it is not automatically a bending operation.
Wood remains in the Wood & Composites material family. See Manufacturing Process Categories for the process model. Wood structure, moisture and engineered-wood products belong to the wood-as-a-material topic; here the question is how to obtain a shape.
What bends, and what retains the shape?
Route
What changes
Main trade-off
Steam bending
One piece is softened, bent over a form and restrained while it sets and dries.
Continuous grain can follow the curve, but stock quality and bend severity strongly affect success.
Kerf bending
Partial-depth slots let the remaining thin web bend; slots close on the inside.
Material removal reduces the intact section and leaves visible or concealed slots.
Bent lamination
Thin strips bend together over a form; cured adhesive holds the assembly.
Repeated curves are practical, but strip preparation, glue lines and springback matter.
Veneering
A thin facing bonds to a substrate, flat or curved.
The base supplies the shape and support; a face veneer alone is not a thick structural member.
Steam makes suitable wood more bendable; the form holds the curve
Steam makes suitable wood more bendable; the form holds the curve
Heat and moisture soften the wood's lignin-rich matrix, allowing the piece to deform more readily. The wood does not become a liquid. It is bent around a form, a shaped support, and held while it cools and dries. Clear, straight-grained white oak and ash are common candidates; species alone does not guarantee a successful bend.
The outside of a bend tends to stretch while the inside compresses. Too much stretching can split the outer fibers; too much compression can wrinkle the inner face. Grain deviations, drying history, moisture, thickness and bend radius all matter. A larger radius is a gentler bend. There is no single radius-to-thickness ratio that works for every piece.
Supporting detail: Addendum 66 — Why heat and moisture work together.
Bent lamination uses thin strips and adhesive to retain a curve; Practice
Bent lamination uses thin strips and adhesive to retain a curve
Thin strips bend more easily than one solid piece of the same total thickness. Bent lamination brings prepared strips together with adhesive over a form, then restrains them until the bond has developed as specified for that adhesive. The strips commonly run with their grain along the curve. Alternating grain direction is not a requirement of bent lamination.
Springback is the tendency for a bend to open when restraint is removed. It can occur in both steam-bent and laminated parts. Thinner laminations can reduce springback for a given total thickness and curve, but adhesive behavior, layer count and material also matter. A trial bend establishes any form compensation; there is no universal correction percentage.
Do not rank every “hot/wet” part above every “cold/dry” part in strength. Compare the actual grain path, remaining section, bond quality, loading and service conditions.
Kerf bending trades an intact section for easier curvature
Kerf bending trades an intact section for easier curvature
A series of partial-depth slots on the inside of the intended curve leaves a thin continuous web on the outside. The slots narrow as the piece bends. Slot depth and spacing, the remaining web and the desired radius determine how it deforms.
This method can suit curved coverings where the slotted side is concealed. It also removes load-carrying material. Filling or bonding the slots does not automatically restore the properties of the original uncut board. A backing or supporting structure may be part of the design; structural performance needs its own justification.
Veneer follows a prepared substrate; it does not replace it
Veneer follows a prepared substrate; it does not replace it
Veneer is a thin wood layer. A substrate is the base it is bonded to. Veneering puts a chosen grain appearance over that base and can cover a flat surface or an appropriate curved form. The substrate must have the intended shape and a sound, even bonding surface.
In book matching, adjacent veneer leaves are opened like book pages to make a mirrored pattern. In slip matching, leaves are placed beside one another in the same orientation for a repeated pattern. Neither arrangement is the same as alternating structural grain directions through a panel's thickness.
Unequal face and back construction can encourage a panel to warp. Veneer thickness, grain, adhesive and the balancing back layer belong in the layup design. Glue selection and detailed bonding methods belong to wood fabrication; engineered panels belong to the material topic.
Materials and Manufacturing Processes/Wood
Drying and Conditioning Wood
Compare drying methods, prepare stock for its service environment and calculate moisture content on an oven-dry basis.
Condition the wood for the environment where it will be used
Condition the wood for the environment where it will be used
Conditioning changes material properties. Drying removes moisture so wood can be prepared for a particular use. It does not permanently freeze the moisture content: dried wood still exchanges moisture with surrounding air. Review the wood-as-a-material topic for the underlying grain and movement behavior.
Not every use requires dried wood, but closely fitted indoor furniture generally does. Choose a target moisture content appropriate to the expected indoor temperature and humidity, then check the actual stock before final machining and assembly. A mill's drying target and a suitable in-service range are not necessarily identical. “Kiln-dried” describes a process; it is not a measurement of what the board contains today.
For indoor furniture in most of the United States, the USDA Wood Handbook recommends 8% average moisture content, with individual pieces at 6–10%, at installation. Regional guidance differs: the dry Southwest uses a 6% average (4–9% for individual pieces), while damp, warm coastal areas use an 11% average (8–13%). Use these as starting points and match the actual service environment. See Table 13–2 and Figure 13–1, page 13–5.
Supporting detail: Addendum 67 — Why the indoor moisture target depends on the building.
Air drying follows the weather; kiln drying controls the conditions
Air drying follows the weather; kiln drying controls the conditions
Two drying routes, often used in sequence
Route
How it works
What it can and cannot do
Air drying
Boards are stacked with spacers called stickers so air can reach their faces, with support and protection from direct rain.
Needs little purchased drying energy, but speed and final moisture depend on climate, species and thickness. Outdoor air drying may not reach the target for heated indoor furniture.
Kiln drying
A chamber controls temperature, humidity and airflow through a drying schedule.
Can reach lower, more controlled moisture levels. An unsuitable schedule can cause cracks, internal damage, distortion or residual stress.
Drying faster is not always drying better. The outside of a board may dry while the center remains wet. Suitable schedules manage this difference; elapsed time or a dry-feeling surface alone does not prove the board is ready.
Radio-frequency and microwave systems both use electromagnetic energy for dielectric heating, but the terms are not synonyms. Industrial systems control frequency, power and moisture removal; this is a process overview, not a household-microwave procedure.
Acclimate stock with airflow and repeated measurements; Checklist
Acclimate stock with airflow and repeated measurements
Acclimating means giving lumber time to approach the conditions in the intended working or service environment. There is no reliable fixed number of days for every board. Thickness, initial moisture, species and humidity all affect the time required.
Identify the intended service environment before choosing the moisture target.
Support boards flat with aligned stickers and space for airflow.
Check several boards and locations with a suitable moisture meter, using its species and temperature corrections where required.
Record repeat measurements and look for stability, not just one favorable reading.
Recheck after major material removal or a change of storage environment before final fitting.
Meter depth and measurement method matter: a surface reading can miss a wetter core. Keep stock in suitable conditions after drying. Joint design still needs to allow movement; see Wood Joinery and Fasteners.
Calculate moisture content using oven-dry mass as the denominator; Practice
Calculate moisture content using oven-dry mass as the denominator
On the oven-dry basis used for wood, MC (%) = (initial mass − oven-dry mass) / oven-dry mass × 100. Both masses must refer to the same sample and use the same units. “Initial” means the sample's mass before the moisture determination; it need not be freshly cut green wood.
For an illustrative sample with initial mass 230 g and oven-dry mass 200 g, the water removed is 230 − 200 = 30 g. Then MC = 30 / 200 × 100 = 15.0%.
Supporting detail: Addendum 68 — Why dividing by the initial mass answers a different question.
Distinguish temporary softening from permanent treatment
Distinguish temporary softening from permanent treatment
Heat and moisture in steaming can soften wood enough for bending. The softening is conditioning; changing the shape is Forming. The part must be restrained as it dries and sets, and some springback can occur. Species, grain quality, thickness and bend radius govern success; there is no universal bending radius for all wood.
Other treatments have specific purposes. Resin impregnation introduces resin into wood; impreg is resin-treated wood, while compreg also uses compression during manufacture. Increased dimensional stability or hardness can come with changes in other properties. Decorative color is not what defines compreg.
Pressure treatment is a delivery method, not a promise of every kind of resistance. Preservative treatment and fire-retardant treatment use different systems for different purposes. Neither the word “treated” nor “pressure-treated” alone establishes water exclusion, chemical resistance or suitability for an application. Use the treatment identification and product specification.
Wood–plastic composites made by combining wood particles or fibers with a polymer are a materials topic. Irradiation is not a universal requirement for making them. Finishing preparation is covered in Preparing and Finishing Wood; chemical handling belongs in Chemicals and Safety Data Sheets.
Materials and Manufacturing Processes/Wood
Wood Joinery and Fasteners
Choose joints and fasteners by the load, glue surfaces, assembly access and movement the connection must allow.
Choose the connection for the load and the grain direction
Choose the connection for the load and the grain direction
Joining separate parts is Fabricating. Start with the direction a load will push or pull, then choose the surfaces that carry it. A shelf needs support underneath; a frame must resist being pushed out of square. A joint that works well for one can be a poor choice for the other.
There is no single strongest joint. Wood species, dimensions, grain direction, fit, adhesive and loading all matter. A snug fit locates parts; it should not require enough force to split them. Most glued joinery is not an engineering interference fit.
Recognize the shoulders, sockets and mating surfaces
Recognize the shoulders, sockets and mating surfaces
Schematic exploded profiles, not cutting dimensions. The colored parts remain separate so the contact surfaces are visible.
Simple joints: geometry, use and limits
Joint
What it is and where it fits
Strength consideration
Butt
One unshaped end or edge meets another piece. Common in simple assemblies.
An end-to-face butt joint offers little resistance to opening without reinforcement. A long-grain edge-to-edge panel joint is a different, often effective glued connection.
Rabbet
A step cut along an edge or end receives another part; useful for cabinet backs and box corners.
The shoulder locates the part and carries load in one direction. Glue or fasteners resist separation.
Dado
A channel across the grain receives a shelf or divider.
The bottom and shoulders provide bearing and location. Too deep a cut weakens the remaining side panel.
Groove
A channel along the grain; useful for a panel edge or drawer bottom.
A groove can retain a panel while allowing it to move. Do not automatically glue a solid panel all around.
Lap
Parts overlap. In a half-lap, material is removed from each so the assembled faces are flush.
A fitted half-lap can give broad glue contact in frames; the cut also reduces each member's section.
Miter
Angled ends meet, often two 45° cuts for a 90° frame corner.
Hides end grain, but an unreinforced corner is vulnerable to opening. A spline, dowel or other reinforcement can help.
Add glue area, alignment or mechanical interlock where needed; Practice
Add glue area, alignment or mechanical interlock where needed
Reinforced and interlocking connections
Joint
Geometry and typical use
What to check
Mortise and tenon
A projecting tongue, the tenon, enters a matching socket, the mortise. Used in rails and legs.
Long-grain cheeks provide glue area; shoulders help resist racking (being pushed out of square). Keep enough wood around the socket.
Dowel
A separate round wooden pin enters matching holes in both parts; used in furniture frames and alignment.
Hole position, depth, dowel size and bonded embedment determine performance. A misaligned hole can prevent the shoulders from closing.
Biscuit
A thin oval insert enters matching slots; useful for aligning panel edges during assembly.
Do not assume an alignment biscuit gives the same reinforcement as a deep dowel or tenon.
Pocket screw
A screw driven through an angled recess joins one part to another; common in face frames.
Use the matching screw and jig setting. Clamp the parts against shifting; leave enough wood for the head and threads.
Box/finger
Alternating rectangular fingers mesh at a corner; common in boxes.
Many glue surfaces resist separation when properly bonded. Straight fingers do not lock against withdrawal as dovetails do. Here “finger” means a box corner, not an industrial end-splice.
Dovetail
Flared tails fit between matching pins; common at drawer corners.
The taper mechanically resists withdrawal in one direction. Thin pins, short grain or poor fit can still fail; orientation matters.
Give screw threads something to grip and the head something to pull
Give screw threads something to grip and the head something to pull
A pilot hole guides the screw and reduces splitting in the receiving piece. A clearance hole lets the screw pass freely through the near piece so its head can pull that piece against the far one. A countersink is a tapered seat for a matching flat head. These holes do different jobs.
Choose pilot diameter from the screw maker's guidance for the wood and screw. A hole that is too small risks splitting; one that is too large removes thread engagement. Threads gripping both pieces before the gap closes can hold the pieces apart.
Use wood screws intended for the application. Drywall screws are intended to attach gypsum board; their head geometry and often brittle behavior make them a poor default for furniture or load-bearing wood joints. Purpose-designed structural screws also differ from ordinary wood screws. Match corrosion protection to the environment and any wood treatment.
Nails are quick to install and many tolerate bending better than hardened screws, but withdrawal resistance depends on shank form and grain direction. Brads are slender finish nails with small heads: useful for light trim and positioning, not a substitute for a designed load-carrying joint.
For repeated disassembly, consider bolts with nuts, cross-dowels, threaded inserts or cam connectors. These knock-down fittings use reusable mating hardware. Capacity still depends on the wood bearing around the fitting, edge distance and the specific hardware, not merely on having metal threads.
Let a wide solid-wood part move across its grain; Checklist; Practice
Let a wide solid-wood part move across its grain
A tabletop fastened rigidly across its width can split or distort as moisture changes. Use a connection designed to permit movement, such as tabletop clips or correctly oriented slotted screw holes. Locate the part while leaving travel in the direction it needs; a screw tightened so hard that nothing can slide defeats the slot.
A frame-and-panel assembly can hold a solid panel in grooves without gluing the panel's perimeter. A manufactured panel may need a different detail: do not assume every wood product moves like solid wood.
Identify the grain direction and the expected load in each part.
Dry-fit the joint and confirm that shoulders close without splitting or distortion.
Check fastener access, edge distance and the intended disassembly method.
Confirm that the attachment leaves room for cross-grain movement.
Match the adhesive to the fit and exposure, then prepare the surfaces and hold the assembly through the specified cure.
Build the joint around sound, closely fitted glue surfaces
Build the joint around sound, closely fitted glue surfaces
Glue needs clean, sound surfaces and a joint designed for the load. For ordinary PVA wood glue, prepare mating surfaces that contact closely without being forced into shape. Paint, finish, dust and old adhesive can prevent a reliable bond.
Long grain is a surface running along the wood fibers; end grain exposes their cut ends. A long-grain edge joint can provide broad, continuous contact. End grain can absorb liquid adhesive rapidly and leave too little at the interface; a plain end-grain butt joint also has limited bonded area and unfavorable loading. End grain can bond, but adding more glue does not automatically make that joint equivalent to a fitted tenon or lap.
Fiber direction and adhesive coverage both matter. The diagram is a simplified comparison, not a strength ranking of every possible joint.
Supporting detail: Addendum 69 — What “stronger than the wood” actually demonstrates.
Choose the adhesive for fit, exposure and repair needs; Practice
Choose the adhesive for fit, exposure and repair needs
Adhesive families: starting points, not product specifications
Adhesive
Useful for
Fit and exposure limits
PVA, including yellow wood glue
Closely fitted wood-to-wood joints in furniture and cabinetry.
Not a structural gap filler. Water resistance varies from interior formulations to products rated for specified wet exposure; color does not establish the rating.
Polyurethane wood glue
Moisture-curing bonds where the product lists the materials and exposure.
Expanding foam is not sound replacement wood in a loose joint. Clamp to control expansion. Do not transfer one product's water rating to the whole family.
Epoxy
Some repairs, mixed-material joints and gaps using a suitable resin, hardener and structural filler.
Mix the specified ratio. A fairing filler meant for easy sanding is not necessarily a structural adhesive filler. Water and temperature performance depend on the system and cure.
Hide glue
Traditional furniture and repairs where future disassembly matters.
Hot hide glue and liquid hide glue have different working times. Close fit is important; heat and moisture can weaken the bond as well as aid repair.
CA (cyanoacrylate)
Small parts, small repairs and rapid positioning.
Thin and gel grades suit different gaps. Short working time and often brittle bonds limit its use for large assemblies or impact loads; check the exact grade.
Construction adhesive
Building assemblies and dissimilar materials listed on the cartridge.
A broad product category, not one chemistry. Bead size, gap limits, compatibility, support time and water resistance are product-specific. It is not automatically suitable for precision furniture joints.
Hot-melt adhesive sets quickly as it cools and is useful for temporary positioning or packaging. Do not assume that quick set gives a durable furniture bond.
Open time is the period after spreading adhesive during which the surfaces may remain apart. Assembly time includes getting the joint together and into clamps; manufacturers may define open and total assembly time separately. Clamp time is how long the assembly must be restrained. Full cure is when the adhesive reaches its specified cured properties under the stated conditions.
These are not interchangeable. A joint that can leave the clamps may still be unready for machining or service loads. Check the exact product's instructions for temperature, moisture, timing and exposure. A fixed “30 minutes for all yellow glue” rule is unreliable.
PVA requires time for water loss and bond development; one-part polyurethane depends on moisture; epoxy working time depends on its resin/hardener system and temperature. Hot hide glue has a short working window as it cools. CA can fix parts very quickly, so trial assembly is especially important. Construction adhesive often needs continued support after initial grab.
Supporting detail: Addendum 70 — Where to find product-specific instructions.
Use clamps to close the joint, not to repair a bad fit; Checklist
Use clamps to close the joint, not to repair a bad fit
Apply enough pressure to seat the surfaces and maintain alignment, following the adhesive instructions. Excess force can dent the wood, bow a panel or force out too much adhesive. A gap that closes only under severe force is a fitting problem.
Bar and pipe clamps span large assemblies; C-clamps apply local pressure; spring clamps suit light holding jobs. Cauls are straight blocks or beams used to distribute pressure and help keep faces aligned. Protect visible surfaces and prevent the cauls from becoming glued to the assembly.
A small, reasonably even bead of squeeze-out can indicate coverage, but it does not prove the entire bond is sound. A dry spot may be hidden inside. Excess glue can seal the surrounding pores and leave a pale patch under stain. Remove it by a method appropriate to the adhesive and surface; do not smear it into a wider area. Inspect again before finishing.
Dry-fit all parts and place the clamps and cauls within reach.
Read the product's assembly, clamp and cure requirements.
Spread adhesive as directed, assemble within its working time and close the joint.
Check alignment, flatness and diagonals where a rectangular assembly must be square.
Inspect squeeze-out and clean surrounding surfaces appropriately.
Keep the joint restrained and unloaded for the specified intervals.
Prepare a uniform surface, distinguish color from protection and choose a finish for appearance, wear and repair.
Remove each grit's scratches before moving to a finer abrasive; Practice
Remove each grit's scratches before moving to a finer abrasive
Start with the least coarse abrasive that removes the actual defects efficiently. Higher grit numbers generally mean finer particles within the same grading system. A possible bare-wood sequence is 80 → 120 → 150 → 180, but sound, smooth stock may start later. Stop at the grit recommended for the chosen stain or finish; 220 is not a universal destination.
Each step removes the previous step's scratches. Jumping straight from a coarse grit to a very fine grit leaves deep scratches that the fine abrasive removes slowly. Inspect under light across the surface, remove dust between steps and replace clogged abrasive. Finish hand sanding along the grain where practical; machine sanding also requires control of pressure and motion.
Do not use prolonged sanding to hide a poorly fitted joint. It can round edges, dish a surface or sand through a thin veneer. Remove glue residue before coloring; a smooth glue patch may still reject stain.
Treat raised fibers, defects and open pores as different problems
Treat raised fibers, defects and open pores as different problems
Water can raise loose fibers and make a previously smooth surface feel rough. When the finishing system calls for it, lightly dampen bare wood, let it dry, then sand the raised fibers lightly with the final preparation grit. This grain raising step reduces roughness under later water-based coats. Heavy sanding can expose fresh fibers and restart the problem.
Preparation products do different jobs
Product or step
Purpose
Check before using it
Defect filler or putty
Fill a small hole or surface defect.
Some products harden and sand; others remain softer and belong after finishing. Color and stain uptake may differ from wood. Sawdust mixed with glue does not reliably stain like the surrounding wood.
Grain/pore filler
Fill open pores for a level surface, especially under a glossy film.
Choose compatible filler and test whether it goes before or after coloring. Filling pores is optional when visible texture is wanted.
Pre-stain conditioner
Reduce uneven stain absorption on blotch-prone wood.
It can lighten or alter the result; it does not guarantee uniform color. Follow the compatible stain system and its timing.
Sanding sealer
Provide a readily sanded initial coating in a compatible system.
It is not required under every finish. The wrong sealer can reduce adhesion or durability.
Bleaching changes wood color chemically; it is not the same as staining. Product chemistry determines the sequence, drying and any required follow-up preparation. Do not use a universal “bleach immediately after final sanding” rule. Consult Chemicals and Safety Data Sheets and Personal Protective Equipment for chemical handling and protection.
Use stain or dye for color, then decide what protection is needed
Use stain or dye for color, then decide what protection is needed
Pigment stain contains fine solid particles that lodge in pores and surface texture. It can emphasize grain and partly obscure it. Dye dissolves in its carrier and can give transparent color; it can still absorb unevenly. Some commercial stains contain both pigment and dye. A gel stain has a thicker consistency and often gives more surface color control on vertical or blotch-prone work.
Coloring alone is not normally the protective finish. Follow the product's application and wipe-off interval: leaving ordinary wiping stain on indefinitely is not a dependable way to make it darker. Test the complete stain-and-topcoat sequence because the clear coat changes the appearance too.
Compare a low-build oil finish with a protective surface film
Compare a low-build oil finish with a protective surface film
Idealized finish families. Real products overlap: an oil–varnish blend can build some film, and film finishes also penetrate surface pores.
Choose by the service conditions and exact formulation
Finish
Appearance and use
Tradeoff
Drying oils, such as linseed or tung oil
Usually applied thinly for a low-build, grain-enhancing surface.
Easy to renew in many applications, but thin oil treatments usually give less wear and spill protection than a suitable film. Drying oil cures; mineral oil does not cure the same way.
Shellac
A resin coating available in different colors; useful for furniture and compatible sealing applications.
Repairable, but vulnerable to alcohol and heat. Check wax content and compatibility before applying another finish over it.
Lacquer
A family of film coatings often used for furniture and sprayed production work.
Many dry quickly; conventional solvent lacquers can be repaired by re-dissolving the surface. Catalyzed products cure differently and are not equally repairable.
Varnish/polyurethane
Film-forming resin systems often selected for wear and spill resistance.
Repair and recoating need preparation. Modern varnishes commonly use synthetic resins. Exterior protection requires an exterior formulation; “varnish” alone does not promise UV resistance.
Water-based clear coatings
Often chosen to retain a lighter color; may use acrylic, polyurethane or blends.
Water-based identifies the carrier, not a separate guarantee of durability. Grain raising and intercoat adhesion need attention. Color change depends on both coating and wood.
Wax or paint
Wax offers a low-build, easily refreshed surface. Paint supplies opaque color in a film.
Wax alone offers limited protection. Paint hides grain and needs compatible preparation, primer where specified, and a suitable topcoat system.
Names such as “Danish oil” or “tung oil finish” may describe blends rather than pure oil. Read the product description. No ordinary finish makes wood completely moisture-proof or eliminates the movement allowance in Wood Joinery and Fasteners.
Match application method and recoat timing to the product
Match application method and recoat timing to the product
Brushing suits many small assemblies; use a compatible brush and maintain a wet edge without repeatedly working a coating that has begun to set. Wiping gives thin, controllable applications when the product is designed for it. Spraying can coat complex shapes evenly but needs suitable equipment, setup and the safety controls in Chemicals and Safety Data Sheets.
Roller coating suits suitable products on broad surfaces. Industrial curtain coating passes panels through a flowing sheet of finish; dip coating immerses parts. Electrostatic spraying requires a suitable coating and process setup to attract charged droplets to the work; ordinary dry wood does not automatically provide that setup.
Build the recommended coats and observe the recoat window. Sand between coats only as directed, with the specified abrasive and after sufficient drying. A fixed 320-grit rule does not fit every coating. Dry-to-touch is not full cure; allow the specified cure before service or final rubbing to adjust sheen.
Choose with a sample board and the expected wear in mind; Checklist; Practice
Choose with a sample board and the expected wear in mind
A frequently wiped surface needs a finish rated for that use; a lightly handled decorative object may favor appearance and easy renewal. Compare resistance to water, cleaning products, abrasion and heat, then consider color, sheen, repairability and available application equipment. A durable film is useful only if it adheres and cures properly.
Prepare a sample of the same wood with the intended sanding sequence.
Test any conditioner, filler and colorant together with the topcoat.
Record products, grits, application method and drying intervals.
Inspect color, texture and adhesion after the specified cure.
Choose the complete system before coating the finished assembly.
Supporting detail: Addendum 71 — Further product-specific preparation guidance.
How bonding, grains and alloy condition affect the properties used to choose a metal.
Metal selection starts with the job the part must do
Metal selection starts with the job the part must do
A metal can carry a load, conduct current, transfer heat or resist wear. Those are different jobs. Start with the required behavior, then compare a particular alloy in a particular condition. An alloy combines a base metal with other elements to change its behavior.
Metallic bonding helps explain conduction and forming
Metallic bonding helps explain conduction and forming
In a metal, some electrons are shared throughout the structure rather than tied to one bond between two atoms. Their mobility helps metals conduct electricity and heat. Metallic bonding can remain intact while atoms rearrange during permanent deformation, which helps explain why many metals can be rolled or drawn.
Most engineering metals contain many tiny crystals called grains. Atoms have an ordered arrangement inside each grain; adjacent grains have different orientations. Grain size, alloy chemistry and processing history all influence properties.
Supporting detail: Addendum 72 — Why two pieces of the same alloy can behave differently.
Strength, hardness, ductility and toughness answer different questions
Strength, hardness, ductility and toughness answer different questions
Mechanical properties used when comparing metals
Property
Question it answers
Selection example
Strength
How much stress can the material withstand? Yield strength concerns the start of permanent deformation; tensile strength concerns the maximum stress in a tensile test.
A loaded bracket must resist permanent bending.
Hardness
How strongly does the surface resist local indentation?
A wear surface may need hardness, but hardness alone does not predict every kind of wear.
Ductility
How much permanent deformation can occur before fracture?
A formed part needs enough ductility to survive bending.
Toughness
How much energy can the material absorb before fracture?
A part struck repeatedly needs resistance to fracture, not simply a hard surface.
Strong does not mean stiff. Stiffness describes elastic deflection. Hardening a steel can raise its strength substantially without a comparable change in its elastic stiffness. Geometry also affects how far a part bends.
Pull a tensile specimen: strength, stiffness, ductility and toughness on one curve; Interactive
Pull a tensile specimen: strength, stiffness, ductility and toughness on one curve
A tension test pulls a specimen of known size until it breaks and records force against stretch. Dividing by the original area and gauge length turns that record into an engineering stress–strain curve, and one curve answers four different questions: how stiff, how strong, how far it stretches and how much energy it absorbs.
The curves below are synthetic teaching curves, shaped to resemble common behaviour. Read the method from them, not the numbers for any real alloy.
Tensile test: one curve, four different properties. This fallback shows the same synthetic curves and calculations as the live lab.
A round specimen with a chosen gauge length L0 = 50 mm and diameter 12.5 mm (original area A0 = 122.7 mm²) is pulled by a moving crosshead. Engineering stress σ = F/A0 (N/mm² = MPa). Engineering strain ε = ΔL/L0 (mm/mm, shown here in %). Both use the original dimensions, so engineering stress falls after the neck forms even though the force is concentrated on a shrinking section.
Synthetic specimen A (ductile, low-carbon-steel-like; illustrative, not a grade). Shaded: area under the curve to fracture. Dashed red line: unloading from 10% strain.
Yield strength (0.2% offset): draw a line with slope E starting at 0.2% strain; where it meets the curve, σy ≈ 250 MPa (at 0.325% strain). Specimen A then stretches along a level yield plateau (stress constant at 250 MPa up to 1.5% strain) before strain hardening makes the curve rise again.
Ultimate tensile strength (UTS): the highest engineering stress, 400 MPa at 20% strain. A neck begins to form after this peak.
Toughness (tensile): the area under the curve to fracture, ∫σ dε ≈ 107 MJ/m³ (1 MPa × 1 = 1 MJ/m³ = 1 J/cm³) of work per original volume. For this gauge volume that is about 659 J. This is not fracture toughness KIC, which is measured on a cracked specimen.
Worked example: unloading leaves permanent set. Stop at ε = 10.0%, where σ = 371 MPa. Removing the load follows a straight line parallel to the elastic slope, so the elastic part σ/E = 371/200 000 = 0.185% springs back. Permanent set = 10.0% − 0.185% = 9.815%, or 4.91 mm on the 50 mm gauge length. Below the yield point the same rule gives zero set: at 0.1% strain and 200 MPa, 0.1% − 200/200 000 = 0.
The same specimen at four moments. Length to scale; the neck shape is illustrative only.
Before loading. Gauge length 50.0 mm (original L₀ = 50.0 mm). Drawn to scale.
At the peak (UTS): stretched uniformly, no neck yet. Gauge length 60.0 mm (original L₀ = 50.0 mm). Drawn to scale.
After the peak: deformation concentrates in a neck. Gauge length 63.5 mm (original L₀ = 50.0 mm). Drawn to scale; neck shape illustrative.
Fractured; pieces fitted together. Broken pieces fitted back together: gauge length 64.9 mm (original L₀ = 50.0 mm). Drawn to scale; neck shape illustrative.
Compare the four synthetic specimens. Each ranks differently on each property: the stiffest is not always the strongest, and the most ductile is not the toughest.
All four synthetic curves on one set of axes; the right panel magnifies the first 1% of strain, where the elastic slopes differ.
A Ductile, low-carbon-steel-like
B Aluminium-alloy-like
C Brittle, gray-iron-like
D Polymer-like (cold drawing)
Read from the four synthetic curves (illustrative; not material data)
Specimen
Stiffness E (GPa)
0.2% offset yield (MPa)
UTS (MPa)
Elongation after fracture (%)
Area to fracture (MJ/m³)
A: Ductile, low-carbon-steel-like
200
250
400
29.8
107
B: Aluminium-alloy-like
70
266
310
12.6
38
C: Brittle, gray-iron-like
100
none: fractures first
215
0.1
0.42
D: Polymer-like (cold drawing)
2.5
36.7
48.0
53.2
21
Specimen C fractures before the 0.2% offset line reaches its curve, so it has no offset yield strength in this test: the value is undefined, not zero. Specimen D (polymer-like) reaches its peak stress early and then draws a neck along the specimen; its offset value is shown only for comparison.
Model, assumptions and sources
The four curves are synthetic: piecewise cubic curves through chosen points, shaped to resemble common behaviour. They are not measurements, grades, certification values or design allowables. Real results depend on composition, processing, specimen geometry, test speed and temperature, none of which are modelled.
Unloading and reloading follow a straight line with the initial elastic slope E (an ideal elastic approximation, no hysteresis). The load never goes below zero: once the unload line reaches zero load the specimen is slack. Permanent set = ε − σ/E, never negative. Elongation after fracture uses the same rule at the fracture point.
The specimen length is drawn to scale. Its thinning before the peak keeps volume constant; the neck and the fracture are drawn only to show where deformation concentrates, not calculated from a necking or fracture law. True stress, strain rate, temperature and hardness are outside this lab.
The area under the curve is work per original volume in this tension test (MPa = MJ/m³). Impact and fracture-toughness tests measure related but different behaviour.
Sources: ASTM E8/E8M, Standard Test Methods for Tension Testing of Metallic Materials (the test method and its definitions; consult the current edition). W. D. Callister Jr. and D. G. Rethwisch, Materials Science and Engineering: An Introduction, chapter “Mechanical Properties of Metals” (engineering stress and strain, modulus, 0.2% offset yield, tensile strength and necking, ductility, toughness as area under the curve, elastic recovery on unloading).
Density, conductivity and corrosion can decide the choice
Density, conductivity and corrosion can decide the choice
Density is mass per volume. Compare equal volumes when comparing densities; a large aluminum part can still weigh more than a small steel part. Use Geometry, Mass, and Force and Dimensional Analysis for mass, weight and unit calculations.
Conductivity describes how readily heat or current travels through a material. Metals vary widely: choosing a good conductor is different from choosing a high-strength alloy.
Corrosion resistance depends on the metal and its surroundings. Stainless steel and aluminum can corrode. Water, salts, trapped moisture and contact with other metals can change performance. A protective surface film helps only while the environment allows it to remain effective.
Supporting detail: Addendum 73 — Why connecting two different metals can change corrosion.
Ferrous means iron-based; a magnet does not identify the grade; Practice
Ferrous means iron-based; a magnet does not identify the grade
Ferrous metals have iron as their base: steels and cast irons belong here. Nonferrous metals have another base, such as aluminum, copper or titanium. Nonferrous does not mean that no trace of iron can be present.
Magnetic response is a clue, not a material certificate. Some stainless steels are weakly magnetic or effectively nonmagnetic in certain conditions. Appearance and a magnet cannot establish an alloy, its temper or its strength.
Carbon, alloy, stainless and tool steels, plus the difference between a steel family and a complete material specification.
Steel is iron-based, with carbon and other elements controlling behavior
Steel is iron-based, with carbon and other elements controlling behavior
Steel contains iron and carbon, often with additional alloying elements. Both composition and processing matter. The same grade can arrive softened for machining or hardened for service.
Use four practical groups: carbon steel, alloy steel, stainless steel and tool steel. These are useful buying categories, not four mutually exclusive chemical definitions: stainless and tool steels also contain alloying elements.
The four steel groups are a selection map. They do not replace grade and condition.
Carbon steel spans easy forming through hardenable cutting edges
Carbon steel spans easy forming through hardenable cutting edges
Relative carbon levels; actual grade limits come from the specification
Group
Typical behavior
Typical uses
Low carbon
Generally readily formed and welded; limited response to ordinary through-hardening.
Sheet parts, brackets and general fabrication.
Medium carbon
More potential for heat-treated strength; forming and welding require more consideration.
Shafts, axles and machinery parts.
High carbon
Can develop high hardness after suitable treatment; less forgiving of forming and impact.
Springs and some cutting tools.
These are trends, not a strength ranking of every item on a shelf. Compare the delivery condition and required properties before substituting one grade for another.
Alloy, stainless and tool steels solve different service problems
Alloy, stainless and tool steels solve different service problems
Choose a family, then qualify a specific grade
Family
Composition idea and purpose
Uses and limits
Alloy steel
Intentional additions such as chromium, nickel or molybdenum adjust properties and heat-treatment response.
Loaded shafts and gears. Alloy steel is not automatically corrosion resistant.
Stainless steel
Chromium supports a protective surface film; other elements adjust performance.
Food equipment, fittings and exposed hardware. Grade, cleaning and environment still matter.
Tool steel
Carbon and alloy additions support hardness, wear resistance or performance at elevated temperature.
Dies, punches and cutting tools. Heat treatment must balance wear resistance against chipping.
Use Heat Treating Metals to distinguish hardening from tempering. Hardenability means the ability to harden to depth under given cooling conditions; it is not the same as a measured surface hardness.
Grade labels identify a material; they are not a heat-treatment recipe
Grade labels identify a material; they are not a heat-treatment recipe
Common labels include 1018 and 1045 for carbon steels, 4140 for alloy steel, 304 and 316 for stainless steels, and O1, A2 and D2 for tool steels. Different designation systems have different rules. Do not apply a four-digit carbon-steel decoding rule to stainless or tool-steel labels.
On an order, identify the governing material specification, grade, delivery condition, form and dimensions. A short grade name alone does not specify strength, hardness, surface finish or dimensional tolerance. Ask for the required certification when traceability matters.
Use the current governing specification or the producer's grade sheet for composition limits and treatment requirements.
Decode carbon and alloy steel numbers; read stainless and tool grades separately
Decode carbon and alloy steel numbers; read stainless and tool grades separately
In the common AISI/SAE four-digit carbon and alloy steel system, the first two digits identify the steel series: 10 is plain carbon steel and 41 is chromium-molybdenum steel. The last two digits give nominal carbon content in hundredths of a percent.
Reading the series and nominal carbon content
Grade
Series
Nominal carbon
1018
10: plain carbon
18 → 0.18%
1045
10: plain carbon
45 → 0.45%
4140
41: chromium-molybdenum
40 → 0.40%
304 and 316 stainless: their chemistries are similar, but 316 has an added alloying element, molybdenum. This improves resistance to chloride exposure and urban or industrial pollution compared with 304.
Tool-steel groups: O1 is an oil-hardening grade, A2 is an air-hardening grade, and D2 is a high-carbon, high-chromium grade. These labels describe different tool-steel groups; they are not carbon-percentage codes.
Supporting detail: Addendum 74 — Sources and quoted designation meanings.
Cast iron is a separate iron-based material, and it can be machined
Cast iron is a separate iron-based material, and it can be machined
Cast irons generally contain more carbon than steels. Their properties depend strongly on how carbon appears in the structure. Gray iron contains graphite flakes and is useful for machine bases and housings where vibration damping matters; it is relatively brittle in tension. Ductile iron contains graphite nodules and can provide much greater ductility.
Casting creates the initial shape. Machining can then finish bores, faces and other accurate features. “Cast” and “machined” are not competing material identities. White cast iron contains substantial hard carbide and behaves differently from graphite-containing irons.
Watch the steel-family series at its original publisher; Practice
Watch the steel-family series at its original publisher
Aluminum, copper alloys, titanium, zinc and magnesium as choices for weight, conductivity, corrosion and manufacturing needs.
Choose the useful property, then check the tradeoff
Choose the useful property, then check the tradeoff
Nonferrous metals have a base other than iron. They are not all lightweight, corrosion-proof or easy to machine. A useful first comparison names both the benefit and the constraint.
Starting points for material selection, not design allowables
Metal
Why choose it?
Typical use and tradeoff
Aluminum
Low density, useful corrosion resistance and ready availability in extruded shapes.
Frames and housings. Lower elastic stiffness than steel; alloy and temper strongly affect strength.
Copper
High electrical and thermal conductivity.
Conductors and heat-transfer parts. Relatively high density and cost; alloying usually reduces conductivity.
Titanium
Useful strength relative to weight and corrosion resistance.
Aerospace and chemical-service parts. Material and processing costs can outweigh the weight saving.
Zinc
Useful casting behavior and ability to protect steel as a coating.
Die-cast hardware and galvanized products. Temperature and load requirements limit use.
Magnesium
Very low density among structural metals.
Light housings. Corrosion protection and suitable manufacturing procedures matter.
Aluminum needs both an alloy label and a condition
Aluminum needs both an alloy label and a condition
Aluminum is sold in many alloys and conditions. Wrought products are shaped by processes such as rolling or extrusion. Their familiar four-digit labels are organized into series, including 1xxx through 7xxx. A series is a family, not a hardness scale: a higher first digit does not guarantee a harder or better part.
6061 and 7075 are common alloy labels to look for in supplier literature. Compare data for the actual product form and temper rather than treating either number as a complete specification. Cast aluminum uses a different designation system; do not transfer wrought-number rules to cast products.
A suffix such as -O or -T6 identifies a condition as part of an alloy-temper designation. It must stay attached to the alloy on an order. See Heat Treating Metals for why processing history matters.
-O: “Annealed” — “Thermally treated to obtain the lowest strength temper.”
-T6: “Solution heat-treated and artificially aged.”
Use the governing product specification for an actual purchase.
Aluminum series 1xxx–7xxx identify purity or the main alloying additions
Aluminum series 1xxx–7xxx identify purity or the main alloying additions
Wrought aluminum series
Series
Principal alloying element or purity
1xxx
Commercially pure aluminum: at least 99% aluminum.
2xxx
Copper.
3xxx
Manganese.
4xxx
Silicon.
5xxx
Magnesium.
6xxx
Magnesium and silicon.
7xxx
Zinc.
Supporting detail: Addendum 75 — Source for the series table.
6061 favors fabrication; 7075 offers higher strength in the T6 condition
6061 favors fabrication; 7075 offers higher strength in the T6 condition
Compare like conditions: 7075-T6 has higher tensile strength than 6061-T6. The alloy number alone does not establish the strength of the material in hand.
6061 and 7075 at selection level
Alloy
Typical uses
Fabrication considerations
6061
Truck and marine frames; tanks.
Weldable and readily machined. Welding can change the temper in the weld area.
7075
Aircraft components, molds and industrial tooling.
Good machinability, but generally considered unsuitable for welding because of cracking susceptibility.
Supporting detail: Addendum 76 — Sources and comparison limits.
Brass and bronze trade some of copper's conductivity for other properties; Practice
Brass and bronze trade some of copper's conductivity for other properties
Brass is principally a copper-zinc alloy. Depending on grade, it can offer useful forming or machining behavior for fittings, hardware and decorative parts. Do not assume every brass has the same machinability or suitability for contact with drinking water.
Bronze traditionally means copper-tin alloy, but commercial names also include aluminum bronze and silicon bronze. Bronzes serve in bearings, bushings, gears and corrosion-resistant hardware, depending on grade. The word “bronze” alone is not enough to buy a bearing material.
For a conductor, begin with conductivity requirements. For a bearing, begin with load, speed, lubrication and wear. The same copper-based family will not automatically win both comparisons.
Recognize stock shapes, distinguish size conventions, and specify enough information to receive the metal a design requires.
Stock is the material shape you buy before making the part
Stock is the material shape you buy before making the part
Stock is material supplied in a usable starting form. Choose a shape that leaves enough material for the finished part and any cutting or machining allowance. Buying the smallest possible shape can fail if saw cuts, surface cleanup or distortion consume the allowance.
Cross-sections show shape only. Dimensions and wall thickness still belong on the order.
Sheet, plate, bar and structural shapes use different size descriptions
Sheet, plate, bar and structural shapes use different size descriptions
What to specify for common forms
Form
Description
Size information
Sheet and plate
Flat products; plate is the thicker category under the applicable product convention.
Thickness, width and length. There is no single sheet/plate boundary for every metal and specification.
Bar
Solid round, flat, square or hexagonal cross-section.
Diameter, width and thickness, square side, or hex size across flats, plus length.
Structural shapes
Angle, channel and I-shaped sections place material where the structure needs it.
Section designation and dimensions, thicknesses and length under the relevant product system.
A gauge number is a sizing convention, not a universal thickness. Specify actual thickness and units when ambiguity would affect the part. Check the applicable material's gauge table if a drawing uses gauge.
Tube dimensions and nominal pipe sizes are not interchangeable
Tube dimensions and nominal pipe sizes are not interchangeable
Tube is commonly ordered by outside dimensions and wall thickness: outside diameter for round tube, or outside width and height for rectangular tube. State the length too.
Pipe commonly uses a nominal pipe size and a wall schedule. A nominal size is a label; it need not equal the measured outside or inside diameter. Use the applicable pipe dimensions table before calculating a fit or flow area. Structural tubing is not automatically suitable for pressure service.
Measure the right boundary. For round hollow stock, inside diameter equals outside diameter minus twice the wall thickness. The wall occurs on both sides of the opening.
Hot-rolled and cold-finished describe processing, not alloy identity
Hot-rolled and cold-finished describe processing, not alloy identity
Hot-rolled steel is shaped at high temperature and commonly arrives with mill scale and comparatively broad dimensional tolerances. Cold rolling or other cold-finishing operations can improve surface finish and dimensional control. Cold-finished bar may be drawn rather than rolled.
Cold work can increase strength and leave residual stresses. Removing material can release those stresses and move the part. Cold-finished does not automatically mean precision ground, and neither term guarantees a particular tolerance without a product specification.
Supporting detail: Addendum 77 — Why an attractive surface can still be the wrong purchase.
A purchase description must preserve alloy, condition, form and size; Checklist
A purchase description must preserve alloy, condition, form and size
An illustrative request is: 6061-T6 aluminum round bar, 25 mm nominal diameter × 500 mm cut length, quantity 2. Before purchasing, add the governing product specification, diameter and cut-length tolerances, finish and certification requirements that the design needs. This example is not a complete engineering specification.
Identify the alloy and required delivery condition from the design.
State the stock form and every necessary dimension with units.
Allow for saw kerf (material lost in the cut), cleanup and final machining.
State tolerances, quantity and any required material certificate.
Compare availability, cut charges, shipping and minimum orders as well as material price.
Confirm that the delivered label and documents match the order before using the stock.
Drops or remnants are leftover pieces that may reduce cost. Their identification and usable dimensions still need checking.
Estimate mass from cross-sectional area, length and density; Practice
Estimate mass from cross-sectional area, length and density
For uniform stock, mass = cross-sectional area × length × density. For a solid round bar, area = πd²/4. For round tube, area = π(D² − d²)/4, where D is outside diameter and d is inside diameter. Subtract the opening before multiplying by length.
Use the density for the actual alloy from a material data sheet and keep units consistent. A result in kilograms is mass; weight as a force also requires gravitational acceleration. See Geometry, Mass, and Force and Dimensional Analysis.
Choose a conditioning process by its goal: soften, refine structure, harden, improve toughness or reduce residual stress.
Heat treatment is conditioning: change structure to change properties
Heat treatment is conditioning: change structure to change properties
Heat treatment uses controlled heating, holding and cooling to change a metal's internal structure. It belongs to Conditioning in Manufacturing Process Categories. It can change properties without intentionally changing the overall shape, although distortion can occur.
The result depends on alloy, starting condition, section thickness and the complete cycle. Heating more or cooling faster is not automatically better. A treatment that strengthens one alloy can soften another.
Supporting detail: Addendum 78 — Steel microstructures are not the four steel families.
Anneal to soften; normalize suitable steels to refine structure
Anneal to soften; normalize suitable steels to refine structure
Annealing is a family of treatments used to soften material, restore ductility or adjust its structure. Full annealing of suitable steels includes slow cooling; annealing cold-worked metal can form new grains and restore formability. Not every anneal uses the same temperature or cycle.
Normalizing heats suitable steel into its austenitic range and then cools it in air. It can refine and make the structure more uniform after earlier processing. Air cooling and slow furnace cooling produce different results.
Choose the process for the desired condition. Do not apply one universal temperature offset to all steels.
Quench hardening usually needs tempering afterward; Practice
Quench hardening usually needs tempering afterward
Quench hardening heats suitable steel to form austenite, holds as required, then cools fast enough to obtain the intended hardened structure. It commonly raises hardness and strength but can reduce ductility and toughness. Cracking and distortion are possible.
Tempering reheats hardened steel below the temperature at which austenite begins to form. It adjusts the balance of hardness and toughness and reduces some quenching stresses. It is not simply heating “just below” one critical temperature; the required cycle depends on grade and target properties.
Separate illustrative cycles, not a furnace program. Peak temperatures, holds and cooling rates are grade-specific.
These concepts explain specifications; they are not operating instructions. Use the approved process for the identified material, equipment and quench medium.
Surface hardening puts wear resistance near the outside
Surface hardening puts wear resistance near the outside
A part may need a hard wear surface and a tougher interior. Carburizing adds carbon near the surface of suitable steel before hardening. Nitriding introduces nitrogen to develop a hard surface layer. These change surface chemistry.
Induction hardening heats a surface region electrically and then quenches it. It uses the steel's existing composition rather than adding carbon. It therefore needs a suitable starting steel. Case depth, surface hardness and core properties must be specified together.
Cold work strengthens; stress relief addresses locked-in stresses; Practice
Cold work strengthens; stress relief addresses locked-in stresses
Work hardening, also called strain hardening, occurs as metal is permanently deformed during cold working. It commonly raises strength and hardness while reducing remaining ductility. “Cold” here means below the relevant recrystallization range, not necessarily cold to the touch.
Stress relief reduces residual stresses left by processing. These are stresses that remain without an external load. The goal is often dimensional stability during later machining or service. Stress relief is not automatically a full softening anneal and does not guarantee zero distortion.
Aluminum strengthening does not use steel's martensite route
Aluminum strengthening does not use steel's martensite route
Some aluminum alloys can be strengthened by solution treatment, quenching and aging. Solution treatment puts selected elements into solid solution; subsequent aging develops small particles that obstruct deformation. Aging can occur naturally or through controlled heating, depending on the alloy and required condition.
Solid-solution strengthening and precipitation strengthening are different mechanisms. Dissolved atoms provide the first; particles of another phase provide the second. Other aluminum alloys obtain much of their strength through cold work. Annealing can soften cold-worked material.
An aluminum temper describes its processing condition. It is not synonymous with the steel process called tempering. Preserve suffixes such as -O and -T6 when reading or writing a material description; consult the relevant alloy-temper specification for their exact meanings.
Supporting detail: Addendum 79 — Further reading on conditioning processes.
Materials and Manufacturing Processes/Metals
Forming Metal
Compare casting, bulk deformation, sheet forming and powder metallurgy by shape, material, tooling and production quantity.
Choose the shape-making route before comparing production cost; Checklist
Choose the shape-making route before comparing production cost
Metal parts can begin as liquid poured into a mold, solid stock plastically deformed into a new shape, or powder pressed into a compact. Plastic deformation means a permanent shape change after the force is removed. Each route limits the shapes it can make and the tools it needs. A die is a tool that controls shape; a mold contains material while it takes shape.
These shape-making routes sit under Forming in the classification used by Manufacturing Process Categories. In metalworking references, forming often means solid-metal deformation specifically, with casting listed separately. Cutting is Separating; joining is Fabricating; property-changing treatment is Conditioning; surface protection or appearance is Finishing. Metals are one of the four families in Material Families, alongside Plastics, Wood & Composites, and Ceramics & Glass. Metal properties and heat treatment are separate topics.
Identify the alloy, overall shape, holes and thin regions.
State the quantity and whether the design will change.
Check tool access and how the part will leave the mold or die.
Compare tooling cost, repeatability and production rate.
Allow for trimming, machining, joining and finishing afterward.
Casting makes a shape by solidifying metal inside a mold
Casting makes a shape by solidifying metal inside a mold
Three casting routes and their trade-offs
Route
How it works
Typical products and cost trade-off
Sand casting
A pattern makes a cavity in bonded sand. Remove the pattern, assemble the mold, pour metal, then break away the mold after solidification.
Pump housings and large machine bases. Relatively flexible tooling can suit small batches; making a new mold for every part adds work.
Investment casting
A disposable pattern, often wax, receives a ceramic shell. Remove the pattern and fire the shell before pouring metal. Break away the shell afterward.
Detailed brackets, valve parts and turbine components. Fine detail can reduce later machining, but pattern and shell preparation add time and cost.
Pressure die casting
Inject molten metal into a reusable metal die, let it solidify, then open the die and eject the part.
Repeated aluminum or zinc housings. Expensive dies and equipment can pay off over long runs; alloy, size and geometry must suit the process.
There is no universal quantity at which die casting becomes cheapest. Obtain estimates for the actual geometry, alloy, tool life and required secondary operations.
Supporting detail: Addendum 80 — Sources for the casting routes.
A casting needs room to release, shrink and feed
A casting needs room to release, shrink and feed
The cope is the upper mold half; the drag is the lower half. The sprue leads downward from the pouring opening, and a runner and gate lead into the cavity. A riser supplies liquid metal as the casting solidifies and contracts. A core occupies space that must remain hollow.
Draft is a slight taper that helps a pattern or casting leave its tooling. A shrinkage allowance changes tooling dimensions to account for contraction. Neither is a universal number: alloy, geometry and process matter. Critical faces or holes may need machining afterward.
Supporting detail: Addendum 81 — Why a larger pattern does not replace a riser.
Rolling squeezes, forging compresses and extrusion pushes through a die
Rolling squeezes, forging compresses and extrusion pushes through a die
Solid-metal forming routes
Route
Shape and examples
Tooling and quantity
Rolling
Rotating rolls reduce thickness or produce a section. Sheet, plate and structural shapes are common products.
Large equipment investment suits substantial throughput; a designer can often buy standard rolled stock.
Open-die forging
Dies compress a solid workpiece without enclosing its whole outline. Examples include large shafts and rings.
Relatively simple dies accommodate varied sizes; repeated positioning and later machining may be needed.
Closed-die forging
Shaped die cavities guide metal flow into repeated parts such as connecting rods and wrenches.
Dedicated tooling favors repeated production. Excess metal may form flash that is trimmed away.
Extrusion
A ram pushes a billet through a die opening. Long channels, rails and heat-sink profiles have a substantially constant cross-section.
A dedicated profile die can serve many lengths. Cut ends, cross holes and local pockets require later operations.
Wire drawing
Pull wire through a reducing die to make it thinner and longer. This is different from pushing stock through an extrusion die.
Die sets and handling equipment suit repeated lengths; several reductions may be needed.
Hot working occurs at temperatures and deformation rates that allow recrystallization, the formation of new grains, during deformation. Cold working occurs where that process does not remove the work hardening as deformation proceeds. The boundary depends on the metal and processing conditions; it is not one temperature for every alloy. Hot rolling permits large shape changes, while cold rolling commonly improves dimensional control and surface quality and can increase strength through work hardening.
Supporting detail: Addendum 82 — Cold forming does not guarantee an unchanged dimension.
Supporting detail: Addendum 83 — Sources for solid-metal deformation.
Sheet forming changes shape; blanking and shearing separate material; Practice
Sheet forming changes shape; blanking and shearing separate material
Bending changes the angle of sheet, as in a bracket or enclosure. A press brake uses a punch and die to make bends; adaptable tooling suits prototypes and short runs. Roll forming progressively bends strip through roll stations into a long profile, such as a channel. Its dedicated roll tooling favors repeated lengths. It is different from rolling sheet thinner.
Deep drawing pulls sheet from a flat blank into a die cavity to make a cup or shell. Tooling must control material flow to limit tearing and wrinkling. Dedicated tools suit repeat production. This is different from pulling wire through a reducing die.
Stamping names a press-based production route that can combine several operations. Bending and drawing are Forming; shearing and blanking are Separating. In blanking, the cut-out piece is the wanted blank; in punching a hole, the removed slug is usually scrap. A stamping line can therefore perform more than one process category.
Bend allowance accounts for the material length within a bend when developing a flat pattern. The sheet stretches on the outside and compresses on the inside. Use a validated bend table or supplier data for the alloy, thickness, radius and tooling; adding outside leg dimensions alone does not give the correct blank length.
Supporting detail: Addendum 84 — Sources for sheet forming and flat patterns.
Powder metallurgy presses particles, then bonds them by sintering
Powder metallurgy presses particles, then bonds them by sintering
In conventional press-and-sinter powder metallurgy, powder fills a die and is compressed into a green compact: a shaped part that is not yet fully bonded. Heating then bonds the particles during sintering, generally without melting the main metal throughout. Some systems include a liquid phase.
Small gears and porous bearings are typical products. Dedicated dies and presses favor repeat quantities and can produce a near-net shape, close to the finished dimensions. Tool access, ejection and density variation limit geometry; critical features may still require sizing or machining.
Supporting detail: Addendum 85 — Porosity can be useful or unwanted.
Compare welding, brazing, soldering and mechanical assembly by joint access, heat input, production needs and service requirements.
Choose a joint around its load, access and need for disassembly
Choose a joint around its load, access and need for disassembly
Joining parts is Fabricating. First identify the metals, thicknesses, loading, service environment and whether the assembly must come apart. Then check access for the joining equipment and for inspection.
A welded frame can avoid a large casting tool, but fit-up, fixtures and inspection still cost money. A bolt-on cover allows service access, but needs clearance for the fasteners and tools. See Fasteners and Galvanic Corrosion for mechanical assembly.
Welding joins the base metal; melting is not required in every process
Welding joins the base metal; melting is not required in every process
Fusion welding melts base metal at the joint, with or without added filler metal. The pool solidifies to form the joint. The common arc, oxy-fuel and resistance spot processes below are fusion processes.
Solid-state welding forms a bond without bulk melting of the base metals. Friction welding is one example. A solid-state process can still heat and alter nearby metal; “not melted” does not mean “unchanged.”
The heat-affected zone is nearby base metal whose structure or properties change because of the thermal cycle, without itself becoming weld metal. Selecting a process includes checking those changes and distortion, not merely whether a bead looks smooth.
Supporting detail: Addendum 86 — Sources for fusion welding, solid-state welding and the heat-affected zone.
Compare the heat source, filler and access of five welding processes; Practice
Compare the heat source, filler and access of five welding processes
Starting candidates for process selection
Process
How it works and where it fits
Trade-off
Oxy-fuel welding
A fuel-and-oxygen flame heats the joint; a separate filler rod may be added. Oxyacetylene can suit selected thin-steel work and repair.
Flexible equipment, but slower and with more broadly distributed heating than many production arc processes.
SMAW / stick
An arc melts a flux-coated consumable rod. The coating supplies protection for the weld pool. Common for steel repair and construction work.
Portable equipment and flexibility; rods need replacement and slag needs removal between appropriate stages.
GMAW (MIG/MAG)
An arc melts continuously fed wire under external shielding gas. Common for repeated steel or aluminum fabrication with suitable wire, gas and settings.
Continuous wire supports production and automation; shielding and equipment access must suit the job.
GTAW / TIG
An arc from a non-consumable tungsten electrode heats the joint under inert gas. Filler, when needed, is supplied separately. Useful for controlled joints in thin stainless steel and aluminum.
Good control of heat and filler, but often slower than wire-fed production welding.
Resistance spot welding
Opposed electrodes press overlapping sheets together and pass current through them, forming a local fused nugget. Common in repeated sheet assemblies.
Rapid repeat joints with suitable equipment and fixtures; conventional arrangements require access to both sides. Separate spots do not make a sealed seam.
Supporting detail: Addendum 87 — Why MIG is a familiar name but GMAW is the broader term.
Supporting detail: Addendum 88 — Sources for the five process mechanisms.
Brazing and soldering melt filler while the base parts stay solid
Brazing and soldering melt filler while the base parts stay solid
In brazing and soldering, a molten filler wets the solid base parts. In a suitable close-fitting joint, capillary action draws filler into the gap. The usual dividing temperature is 450°C: the American Welding Society describes brazing fillers as having a liquidus above 450°C and soldering fillers below it. Liquidus is the temperature above which the filler is fully liquid. This distinction concerns the filler, not the flame temperature or the machine's setting. In both processes the base parts remain solid. Neither is simply a cooler version of fusion welding.
Brazing can join suitable dissimilar metals or attach a carbide tip to a steel tool body. Soldering is common in electrical connections. Choose filler and joint design for compatibility, temperature and loads; a soldered electrical connection is not automatically suitable for a structural load.
Joint clearance, surface condition and heating method matter. Brazing can be manual or performed in production equipment such as a furnace. Mechanization changes throughput and tooling costs; the process name alone does not identify the cheapest route.
Supporting detail: Addendum 89 — Sources for the filler-temperature distinction and capillary joint.
Specify the required joint, not just the name of the machine; Checklist
Specify the required joint, not just the name of the machine
Identify both base materials, thicknesses and any coatings.
Describe the joint location, overlap or preparation and equipment access.
State load, leak-tightness and appearance requirements.
Allow for distortion, inspection and any later machining.
Coordinate the finish and any assembly sequence constraints.
A drawing and its referenced specification communicate the required weld and acceptance criteria. A process abbreviation alone does not specify weld size, extent or quality. Likewise, a visually neat joint does not establish internal soundness. Heat-treatment selection is a separate topic.
Materials and Manufacturing Processes/Metals
Fasteners and Galvanic Corrosion
Choose mechanical joints for service access, thread compatibility and exposure to moisture and dissimilar metals.
Match the fastener to the assembly and its service access
Match the fastener to the assembly and its service access
Common mechanical joining components
Component
Purpose
Design check
Bolt and nut
Provide a removable threaded connection that can clamp parts together.
Provide tool access, suitable thread engagement and a compatible strength and material specification.
Washer
Provides a bearing surface or distributes load where the design requires it.
A plain washer does not by itself prevent loosening or electrically isolate an entire joint.
Rivet
Forms a retaining head through permanent deformation.
Suitable for repeated sheet assembly; removal normally destroys the rivet. Blind rivets permit installation from one side.
Threaded insert
Provides an internal thread in a host part.
Select an insert designed for the host material and thickness. Check installation access, pull-out and resistance to rotation.
Standard fasteners often reduce dedicated tooling for short runs, but every fastener adds parts and assembly time. Riveting or automated fastening may suit long runs. Removability, inspection and repair can justify a threaded joint even when another method is faster.
A thread size alone does not specify a complete fastener; Practice
A thread size alone does not specify a complete fastener
The mating threads must agree in diameter, spacing and thread system. Similar-looking inch and metric parts are not interchangeable. Pitch describes axial spacing between adjacent thread forms; threads per inch describes a count over a unit length.
A purchase or drawing specification also needs the relevant length, head style, material or strength grade, coating and thread-fit requirements. The wrench size is not the thread diameter. Use the applicable thread reference and supplier drawing to decode a designation before choosing mating parts.
Read diameter and thread spacing separately
Example
Diameter
Spacing and system
1/4-20 UNC
Nominal thread diameter: 1/4 inch.
20 threads per inch; UNC is the Unified coarse series. The pitch is 1/20 inch, not 20 inches.
M6 × 1
Nominal metric thread diameter: 6 mm.
Pitch: 1 mm between corresponding points on adjacent threads. The 1 is not a count of threads per inch.
These are thread-size examples, not complete fastener specifications. Nominal diameter identifies the size; tolerances govern the actual mating dimensions. A 1/4-20 thread and an M6 × 1 thread differ in both diameter and spacing.
Supporting detail: Addendum 90 — Sources for thread names and size examples.
Galvanic corrosion needs a metal pair, electrical contact and an electrolyte
Galvanic corrosion needs a metal pair, electrical contact and an electrolyte
Dissimilar metals can form a corrosion cell when they are electrically connected and share a conductive liquid, called an electrolyte. Moisture containing salts can provide that liquid. The more active member of the pair acts as the anode and may corrode faster; the other acts as the cathode.
A galvanic series ranks metals by their behavior in a specified environment. It helps screen combinations; it does not predict a service life. Alloy condition, surface films, wetting and exposed areas matter. A dry pair is not automatically a working galvanic cell.
Supporting detail: Addendum 91 — Why the wetted areas matter.
Supporting detail: Addendum 92 — Sources for galvanic contact, coatings and area effects.
Review the complete joint before calling a fastener compatible; Checklist; Practice
Review the complete joint before calling a fastener compatible
“Stainless” does not mean compatible with every metal, and a coating is not a permanent guarantee of isolation. Consider material pairing, durable electrical separation, drainage and a suitable protective finish together. An insulating washer under a head does not isolate a shank that still touches the hole wall.
Identify the base metal, fastener, washer and their coatings.
Identify where electrical contact and moisture can occur.
Check the material pairing for the actual service environment.
Review sleeves, washers or gaskets for complete isolation and mechanical suitability.
Provide drainage and an inspectable, maintainable finish.
Compatibility review does not replace structural sizing or joint design.
Materials and Manufacturing Processes/Manufacturing Documentation
Critical Dimensions for the Shop
Choose dimensions from fit, function and interfaces, then give the maker and inspector the same references and limits.
A critical dimension controls fit, function or an interface
A critical dimension controls fit, function or an interface
A critical dimension is one whose variation can stop the part doing its job. Start with what touches another part, what must move or clear, and what locates the part. A hole's diameter may control whether a pin enters; its position may control whether two parts line up.
Critical does not mean “make every tolerance tight.” A tolerance is the permitted variation in a dimension. Choose it from the function, then check that the process and inspection method can achieve it. See Tolerances and Fits for limits and fits, Measurement Language for units and measurement language, and Surface Texture and Finish for surface requirements.
Give hole locations from named reference edges
Give hole locations from named reference edges
The original DL-01 display plate below illustrates a shop drawing. Its two suspension holes must stay at the intended locations; length and width mainly establish the display area. These are invented teaching limits, not a general specification for plywood or hanging hardware.
All dimensions in mm. Not to scale for measurement. L and B are plain-language reference labels, not formal geometric-tolerancing datum symbols. C marks the dimensions selected as critical for this example.
Display area and thickness. Measure with calipers; check adjacent edges with a try square for no visible gap.
C — two through holes
Each diameter 4.5 ±0.2 mm.
Openings for the loops; use suitable plug gauges for 4.3–4.7 mm limits.
C — center positions
From L: x = 15 ±0.5 and 85 ±0.5 mm. From B: y = 20 ±0.5 mm for each.
Consistent suspension locations. Check each coordinate from the stated edge.
Surface and edges
No coating; no loose fibers, splits or separated plywood layers.
Visual inspection after sanding; retain the dimensional limits.
All features have requirements, including those not marked C. See Operation Method Sheets for the manufacturing sequence and Bills of Materials for the matching parts list.
Worked record: correct horizontal separation, wrong locations
For this classroom comparison with DL-01 revision A, treat the following readings as exact mm values. The near-edge readings run horizontally right from L and vertically up from B to the nearest edge of each hole. Calculate each center using that hole's measured diameter.
Left hole: diameter 4.6; near edges 13.3 from L and 17.2 from B. Center x = 13.3 + 4.6/2 = 15.6 mm; y = 17.2 + 4.6/2 = 19.5 mm.
Right hole: diameter 4.4; near edges 83.4 from L and 18.3 from B. Center x = 83.4 + 4.4/2 = 85.6 mm; y = 18.3 + 4.4/2 = 20.5 mm.
Record the comparisons: both diameters meet 4.3–4.7 mm. Left x = 15.6 exceeds 15.5; right x = 85.6 exceeds 85.5, so both x locations fail. Both y locations meet 19.5–20.5 mm, including its endpoints. The horizontal separation is 85.6 − 15.6 = 70.0 mm, the nominal x-coordinate difference, but the pair is shifted right. These hole readings do not meet the drawing's separate location limits; correct horizontal separation alone does not locate the pair. This record compares only the stated hole readings, not the outline, thickness or surface requirements.
Supporting detail: Addendum 93 — How to check a center when a caliper touches the hole edge.
Dimension the part so it can be made without measuring the picture; Checklist; Practice
Dimension the part so it can be made without measuring the picture
Include the part identity, revision, material, units, overall dimensions, feature sizes and locations, thickness, and required finish. Supply enough views to remove ambiguity. Call a hole “through” when it passes through the material; otherwise specify depth.
Locate related features from a common reference where that matches their function. Do not give multiple independent dimensions for the same feature unless their relationship is clear. A redundant dimension can contradict the dimensions used to make the part.
Identify every mating surface, clearance and locating feature.
Choose references the maker can establish and the inspector can reach.
Check that each feature has a size, location and acceptance limit.
Remove conflicting or missing dimensions; do not rely on drawing scale.
Match the drawing revision to the method sheet and BOM.
Materials and Manufacturing Processes/Manufacturing Documentation
Bills of Materials
List the parts in an assembly and estimate each part's material share without confusing stock purchases with per-part consumption.
A bill of materials says what goes into one assembly
A bill of materials says what goes into one assembly
A bill of materials (BOM) lists the parts needed for a product. Give each part a stable number, a clear name, a quantity per assembly, a material and a make-or-buy designation. Identify the stock for made parts and the purchasing description for bought parts.
Made means the part needs a drawing and a route such as an operation method sheet. Bought means it arrives as a component; it still needs a size and specification so the buyer can obtain the correct item. Match the BOM revision to the assembly drawing. State whether quantities are per assembly or for the whole batch.
Material cost per part is its allocated stock share times stock price
Material cost per part is its allocated stock share times stock price
Estimated material cost per part = stock share allocated to that part × price of that stock unit. Keep both amounts on the same basis: length for constant-section bar, area for sheet of the same thickness, or mass when purchased by mass.
Allow for the saw cut's width (kerf), trimming and unusable stock. Finished-part volume alone can understate what making the part consumes. State how you allocate waste and reusable leftovers so two estimates can be compared.
Supporting detail: Addendum 94 — Consumption, purchase cost and batch yield answer different questions.
Worked BOM: one display label assembly costs $1.20 in allocated materials
Worked BOM: one display label assembly costs $1.20 in allocated materials
This original example matches DL-01 in Operation Method Sheets and Critical Dimensions for the Shop. All prices are invented teaching values, not quotations. Assembly DL-A, revision A, contains one made plywood plate and two purchased closed cord loops.
The 110 × 50 × 6 mm starting blank is allocated a 120 × 60 mm area of a 1200 × 120 × 6 mm birch plywood strip costing $18. The larger allocation includes room for cutting and trimming. Allocation share = (120 × 60) / (1200 × 120) = 0.05. Plate material estimate = 0.05 × $18 = $0.90.
DL-A revision A — quantities and material estimate per assembly
Part number / name
Make / buy; material and stock
Quantity
Cost each
Extended cost
DL-01 / display label plate
Make; birch plywood, blank 110 × 50 × 6 mm; allocated stock area 120 × 60 mm as above.
1
$0.90
$0.90
DL-02 / closed cord loop
Buy; waxed cotton cord, 1 mm diameter, 100 mm closed-loop circumference; example pack of 20 for $3.
2
$0.15
$0.30
Total allocated material and purchased-component cost per assembly
$1.20
Extended cost is quantity × cost each. The $1.20 excludes labor, machine time, tooling, consumables, taxes and delivery. It is not a complete manufacturing cost or a selling price. Broader cost roll-up and design-for-manufacturing decisions belong with manufacturing economics.
Buying one strip and one pack costs $21, even for one assembly. Unused material remains inventory; do not confuse that purchase total with $1.20 of allocated consumption.
Check quantities, units and waste before totaling the BOM; Checklist; Practice
Check quantities, units and waste before totaling the BOM
Match every drawing part number to a BOM row.
State the quantity per assembly and multiply once for the batch quantity.
Specify stock dimensions and material for made parts, and purchasing details for bought parts.
Use the same units in the stock-share numerator and denominator.
Document the cutting allowance and treatment of leftovers.
Multiply each quantity by its unit cost and sum the extended costs.
Keep unrounded intermediate calculations; round money to cents at the stated reporting step.
Materials and Manufacturing Processes/Manufacturing Documentation
Operation Method Sheets
Turn a drawing into an ordered plan with equipment, setup, process settings and a check that proves each operation is complete.
A method sheet tells another person how to make and check the part
A method sheet tells another person how to make and check the part
A drawing describes the required part. An operation method sheet describes how to make it. A process plan or routing sheet serves the same planning purpose, although the amount of detail varies. Write one row for each operation, in the order it will be performed.
Start with the part number and name, drawing revision, date, material and raw stock size: the starting piece before machining or cutting. Use actual dimensions and units. A material family alone is not a purchasing specification; identify the material needed for this part.
What belongs in each operation row
Field
What the next person needs
Operation
An action and its intended result, such as drill two through holes.
Equipment and setup/tooling
The equipment, cutting tool, support, holding method and reference face or edge.
Process parameters
Settings with units, or an identified approved setup instruction. Do not write an unexplained number for speed or feed.
Setup and cycle time
Time to prepare the operation, separate from time to repeat it on one part.
Pass/fail criteria and inspection tools
The required result, permitted limits and how to measure or compare it.
Keep quality checkpoints, failed-part decisions, actual times and improvement notes with the sheet. Equipment permission and operating procedures still come from Equipment Operating Procedure; a method sheet is not machine training.
Establish reference surfaces before locating features
Establish reference surfaces before locating features
Choose the order around what each later step needs. Make a straight, square reference edge before measuring hole locations from it. Make features while there is enough material to support and hold the work. Inspect a feature before the next step hides it.
This is a planning pattern, not a mandatory route for every part.
Holes may be easier to make before small parts are cut free from a larger piece. Final finishing usually follows cutting and drilling, so those operations do not damage the finished surface. Inspect afterward too: finishing can change dimensions.
Supporting detail: Addendum 95 — Why there is no universal operation order.
Worked method sheet: a hanging display label
Worked method sheet: a hanging display label
Original teaching example, not a production release. Part DL-01, display label plate, revision A. Material: birch plywood, starting blank 110 × 50 × 6 mm. Finished dimensions and acceptance limits are on the example drawing. Two purchased cord loops complete the assembly in Bills of Materials. No coating is specified.
This hand-tool route uses a supported blank, a fine-tooth handsaw, a drill press and sanding blocks. An actual shop must qualify its tooling and record machine settings before releasing the plan. The times below are invented planning estimates, not measured performance.
DL-01 revision A — route and inspection
Operation
Equipment, setup and parameters
Pass/fail check and tool
10 — Establish edges and trim
Bench, clamps, handsaw and sanding block. Support the blank; establish straight bottom edge B and left edge L square to it. Mark the final outline from B and L, saw outside it, then sand to the lines.
Calipers: length 99–101 mm; width 39–41 mm; thickness 5.5–6.5 mm. Try square: no visible gap along the checked edges against the blade. Reject split or separated plywood layers.
20 — Locate two hole centers
Rule, square and marking tool. From L mark x = 15 and 85 mm; from B mark y = 20 mm for both. Keep the same references for both holes.
Rule and square: confirm both marks against the drawing before drilling; this layout check does not replace finished-hole measurement.
30 — Drill through
Drill press, 4.5 mm wood-cutting bit, backing board and clamped work. Record the qualified spindle speed in rpm and the approved drilling setup before use.
Hole diameter 4.3–4.7 mm using suitable plug gauges; hole-center x and y coordinates within ±0.5 mm of the drawing using calipers and measured hole diameter. No splits at the holes.
40 — Finish and inspect
Sanding block, example sequence 120 then 180 grit. Remove loose fibers at edges and hole mouths without enlarging holes beyond their limits.
Visual inspection: no loose fibers, splits or separated layers. Recheck dimensions and hole limits using the tools above.
50 — Add two cord loops
Hand assembly. Thread one purchased closed loop through each hole, then pass the rest of that loop through its emerging end to form a hitch. Seat both hitches alike.
Visual comparison: two closed loops present, one through each hole, each hitched around the plate edge with no loose cut end. This is a display example, not a load-rated hanger.
Planning time per operation, minutes
Operation
Setup per batch
Cycle per assembly
10
3
5
20
1
2
30
4
2
40
1
3
50
1
1
Total
10
13
For three assemblies, the serial estimate is 10 + (3 × 13) = 49 minutes, assuming each setup is done once and all operations run one after another. Record waiting, interruptions and repeated setups separately when comparing with actual elapsed time.
Replace “make it right” with an action and an acceptance test; Checklist; Practice
Replace “make it right” with an action and an acceptance test
“Drill the holes neatly” leaves the next person guessing. “Drill two through holes at the drawing coordinates; check diameter and location against revision A” gives an action and a result, but still needs the equipment, support, tooling and settings in the row.
Pass means every stated criterion is met. Fail means identify and hold the part for a decision; do not quietly send it to the next operation. Rework is a specified additional operation that can bring the part into conformance. Removing more material cannot restore an undersize outside dimension or shrink an oversize hole.
Match the part, drawing and method-sheet revisions.
Check that every operation names equipment, tooling, holding and references.
Fill required settings with units before releasing the plan.
Give every quality checkpoint a measurable limit or an explicit comparison and an inspection method.
Define who decides rework or rejection when a check fails.
Record what changed so the next batch can repeat the improvement
Record what changed so the next batch can repeat the improvement
Record setup time once per setup and cycle time per piece. State when each timer starts and stops; include inspection consistently. Keep quantity attempted, quantity accepted, scrap count and rework count. A reworked part may later pass, so these counts are not all separate groups to add together.
For each trial, record material identity, tool, setting and units, holding arrangement, actual measurements and the problem observed. A useful photo shows the reference edge, stop or tool position; caption it with the operation and revision. Use photos you have permission to share, with no personal information.
Example improvement record — a proposed trial, not a claimed result
Observation
Change to test
Evidence to keep
Hole locations vary between pieces.
Use the same reference edges and a verified locating stop instead of re-marking from different edges.
Record each hole location before and after the change, batch size, setup time and rejects. Keep the acceptance limits unchanged.
Change one factor at a time where practical. Verify the first piece after a setup change before repeating it through a batch. If the change helps, update the method-sheet revision and keep the evidence. A faster operation that produces more rejects is not automatically an improvement.
Materials and Manufacturing Processes/Manufacturing Documentation
Making Silicone Molds from a Printed Pattern
Plan a one-part mold, document the product-specific mixing and curing conditions, and inspect a repeatable batch of castings.
A printed pattern defines the cavity in the silicone mold; Interactive; Practice
A printed pattern defines the cavity in the silicone mold
A pattern is the original shape copied by a mold. For a simple one-part, open-face mold, use a shape with a flat back and features that can be withdrawn through the opening. An original example is a small decorative relief tile with a flat back, gently sloping sides and no hooked details.
For a small batch of resin replicas, this is a casting task: liquid resin fills the mold cavity and cures. A fiber-reinforced shell made by wet hand layup builds layers of reinforcing fabric or mat with resin against a mold. Compare these routes in Plastic Forming Processes, then use Choosing a Plastic Forming Process to weigh material, geometry, quantity and tooling. Try the detailed-replica and reinforced-shell practice choices.
Draft is a slight taper that helps a part leave the mold. Let the shape widen toward the opening. A flat parting face, where the pattern meets the mold-box base, defines the open back of this mold. Avoid undercuts that hook behind the silicone; flexibility does not make every trapped shape removable.
A wide mouth does not rule out an interior hook. This illustrative model uses an exact-fit, centered, symmetric rigid 2D pattern and rigid cavity. Opening depth is 0; positive depth points down into the mold. The only permitted motion is outward translation upward at fixed orientation, into unobstructed space. Units are arbitrary consistent diagram units.
Hypothetical local-shoulder pose at outward pull 5. The original depth-25 section moves to cavity depth 20: pattern half-width 26 meets cavity half-width 22, a geometric overlap of 4 per side. Outlined bands and × marks locate interference; this is not physical passage through rigid material.
Exact piecewise-linear sections: stations are (depth, half-width)
Profile
Stations
Trial pull 5
Whole path
Taper
(0,30), (40,20)
1.25 side separation
No positive interference
Parallel
(0,25), (40,25)
Side contact
No positive interference; contact persists
Reverse taper
(0,20), (40,30)
1.25 interference per side
Blocked
Local shoulder
(0,30), (20,22), (25,26), (40,15)
Maximum 4 interference per side at depth 20
Blocked despite widest mouth
At cavity depth d, an outward pull t places pattern half-width w(d+t) against cavity half-width w(d). Positive Δ(d) = w(d+t) − w(d) means overlap. For the local shoulder at t = 5, the positive interval is (50/3, 520/23), approximately (16.6667, 22.6087); endpoints are zero-contact boundaries.
The continuous path requires width to be nonincreasing with depth. A deeper section wider than a shallower section provides an obstruction. For each pose, Δ is linear between original and translated knots; checking these knots and solving zero crossings is analytical, not an animation-frame test. At t = 0 every profile is in initial contact. At t = 40 there is no interior overlap, but the reverse taper and local shoulder still have blocked paths: a clear endpoint does not prove a reachable endpoint.
Comparisons use a numerical threshold of 64 × machine epsilon × maximum half-width, separate from physical clearance and manufacturing tolerance. Values within that floating-point threshold are treated as contact. This is geometric interference only: it omits friction, adhesion, shrinkage, forces, damage, cure, rotation, lateral motion, deformation and unshown 3D features. No-interference does not establish practical release; a rigid obstruction does not establish flexible-silicone failure.
The mold copies the pattern's surface. Smooth and inspect the print before making the mold.
Remove unwanted layer ridges and support marks without losing important dimensions. Choose pattern preparation, any sealer and any release agent for the specific print, silicone and casting material. Follow the manufacturers' compatibility instructions and test a small prepared sample before committing the full mold.
Read the technical data sheet before choosing a mix or cure schedule; Checklist
Read the technical data sheet before choosing a mix or cure schedule
The technical data sheet (TDS) supplies processing instructions. The safety data sheet (SDS) supplies handling information; use Chemicals and Safety Data Sheets for that guidance. Neither a generic lesson nor a familiar-looking container replaces the instructions for the actual product.
Record the silicone product, batch identification and technical-sheet revision.
Record the A:B ratio and whether it is by mass (weight) or by volume.
Record working time, mixing procedure, bubble-removal requirements and cure conditions.
Check compatibility with the printed pattern, coatings, release agent and intended casting material.
Complete a small compatibility trial and inspect its cure before the full pour.
Working time is the available time to mix and place the material under stated conditions. It is not the demolding time. Cure instructions may distinguish demolding from full properties or further treatment. Record the actual temperature and times; do not substitute a universal overnight wait.
Supporting detail: Addendum 96 — Where to find product-specific instructions.
A ratio by weight is not automatically a ratio by volume; Interactive; Practice
A ratio by weight is not automatically a ratio by volume
Read what the given mass represents. These invented A/B examples teach arithmetic for two-component materials; they are not silicone or resin recipes. For A:B = a:b by mass and target total material mass M, mA = M a/(a+b) and mB = M b/(a+b). If A is already measured, mB = mA b/a.
Same 10:1 mass specification, different meaning of 220 g
Given
A
B
Material total
220 g target total
200 g
20 g
220 g
220 g of A alone
220 g
22 g
242 g
Density connects mass and each component’s own volume: VA = mA/ρA and VB = mB/ρB. For a:b by volume, divide target total mass using weights aρA:bρB. For given A mass, VA = mA/ρA, VB = VA b/a, then mB = VBρB.
Use illustrative densities ρA = 1.2 g/mL and ρB = 0.8 g/mL with a 300 g target total:
Changing the basis while keeping 2:1 changes the specification
A:B specification
A mass / volume
B mass / volume
2:1 by mass
200 g / 500/3 mL (≈166.6667 mL)
100 g / 125 mL
2:1 by volume
225 g / 187.5 mL
75 g / 93.75 mL
The first row has a 4:3 component-volume ratio; the second has a 3:1 mass ratio. Those are equivalent descriptions of their respective batches. Converting 300 g to 0.3 kg keeps the same physical batch. Switching 2:1 from mass to volume does not. Individual component volumes do not establish mixed/cured volume, yield or cavity fill.
Ideal cumulative scale example: for 200 g A + 20 g B in a 35 g container, readings with no tare are 35 g empty → 235 g after A → 255 g after B. Tare once with the empty container on the scale and the readings are 0 g → 200 g → 220 g. The final reading includes A and B; B alone is 20 g. Container mass changes the gross reading, not the material ratio. This comparison does not re-tare after A.
Weigh with a scale suitable for the actual quantities and follow the product’s specified ratio basis, measurement and mixing procedure. The arithmetic assumes no material loss; it predicts no cure, exotherm, working time, compatibility or actual mixed/cured volume. The actual product’s TDS/SDS remain authoritative.
Document pattern preparation, pouring and cure as separate operations
Document pattern preparation, pouring and cure as separate operations
Prepare the pattern and box. Inspect the print, complete the qualified surface treatment, secure its flat back to the box base, and check that the box contains the liquid. Set wall and backing thickness from the mold material and geometry requirements.
Measure and mix. Record actual A and B quantities, the ratio basis and the start time. Follow the product's mixing instructions, including its directions for reaching material at the container walls and bottom.
Reduce trapped air. Follow the product's bubble-removal and pouring instructions. A controlled pour into a low point can let the material rise around the pattern instead of repeatedly trapping air over its details. Vacuum degassing is product- and equipment-dependent; do not assume every silicone requires it or has enough working time for it.
Cure and remove the pattern. Record temperature, elapsed time and the specified demolding condition. Inspect the mold surface and details after removal before using the cavity.
Make a first casting. Follow the casting material's own mixing, release and cure instructions. Its ratio and timing need not match the silicone's. Inspect the first piece before repeating the batch.
Use Operation Method Sheets to give each operation equipment, settings, timing and a pass/fail check. Record what actually happened, including a changed pour method or a delayed demold, rather than copying the planned values into the result column.
Inspect each casting for voids, dimensions and consistency
Inspect each casting for voids, dimensions and consistency
A void is an unintended empty region. Inspect visible faces, edges and small details for pits, missing material and incomplete filling. A good exterior does not prove that the interior has no voids; choose further inspection according to the part's function.
Define batch checks before casting
Check
What to document
Shape and dimensions
Drawing limits, measurement method and actual readings for critical features.
Visible surface
Which faces matter and what counts as a reject. For a teaching relief tile, an example criterion is no visible pits or missing raised detail on the display face.
Cure and release
Product-specific acceptance condition; any tacky region, tearing or distortion observed on removal.
Batch consistency
Casting number, material batch, measured charge, mixing and cure times, appearance, dimensions, rejects and rework.
If a defect repeats at the same position, inspect the corresponding mold feature. If it varies between pours, compare the recorded process conditions. These are starting points for investigation, not proof of a cause. Change one factor, make a trial, and retain the results before revising the approved method.
Materials and Manufacturing Processes/Foundations
Manufacturing Cost and Volume
Estimate unit cost and find where two production methods cost the same.
Count material, processing, quality and overhead costs once
Count material, processing, quality and overhead costs once
Material, labor, machine time, tooling and scrap all affect the cost of an acceptable part. Setup prepares an operation; cycle time is the time for a repeating operation.
Material: stock purchase, delivery and material lost during production.
Processing: labor, machine time, tools, consumables and energy.
Quality: prevention, inspection, rework, rejects and returns.
Overhead: shared support such as facilities and indirect labor.
Check what a machine rate already includes before adding labor, energy or depreciation. Scrap belongs in the estimate once, even if it appears under both material and quality headings.
Spread fixed cost over the quantity actually needed; Practice
Spread fixed cost over the quantity actually needed
For a simple batch model, C = F + vQ and u = C/Q = F/Q + v. C is total cost, F is fixed batch cost, v is variable cost per part, Q is the number of acceptable parts, and u is average unit cost. Use Q greater than zero.
Fixed cost stays constant within the stated production range; variable cost grows with quantity. Setup and dedicated tooling may be fixed for a batch. Material and processing per part often contribute to v. State the period and cost boundary before classifying a cost.
Illustrative process A costs $120 + $8Q. At 60 parts, total cost is $600 and unit cost is $10.00/part. Producing unwanted parts to spread fixed cost creates inventory; it does not create demand.
Supporting detail: Addendum 97 — Why a shorter cycle does not reduce every cost equally.
Set total costs equal to find process break-even; Practice
Set total costs equal to find process break-even
Compare routes that meet the same requirements at the same quantity. From F_A + v_A Q = F_B + v_B Q, obtain Q* = (F_B − F_A)/(v_A − v_B).
Let A cost $120 + $8Q and B cost $720 + $3Q. Then Q* = ($720 − $120)/($8 − $3) = 120 parts. Both cost $1,080 total or $9/part. A costs less below 120; B costs less above 120.
Supporting detail: Addendum 98 — When there is no positive crossing.
Move the volume slider and predict which process wins; Interactive
Move the volume slider and predict which process wins
Start with the original A/B costs and predict the cheaper process at 60 and 240 parts. Then change a setup cost or variable cost and compare at the same demanded quantity. The case selector also includes fractional crossings, parallel lines, an everywhere tie, and a crossing beyond the chart.
Process-cost explorer. Compare C = F + vQ and u = F/Q + v for two routes supplying the same demanded quantity of equivalent acceptable parts in one batch. Use the same included costs and period for each route, count each cost once, and assume the entered rates stay constant. The exercise does not establish equivalent quality, capacity or demand, or recommend a purchase.
Predict, calculate total cost for each route, then divide by the demanded quantity. With A = $120 + $8Q and B = $720 + $3Q:
Original comparison at three demanded quantities
Parts
A total / per part
B total / per part
Lower cost
60
$600 / $10.00
$900 / $15.00
A
120
$1,080 / $9.00
$1,080 / $9.00
Equal
240
$2,040 / $8.50
$1,440 / $6.00
B
Between whole parts: let A = $90 + $6Q and B = $245 + $2Q. Q* = 155/4 = 38.75 parts. At 38 parts A totals $318 and B $321; at 39 parts A totals $324 and B $323. No whole-part quantity ties.
Try the other cases: A = $60 + $4Q and B = $210 + $4Q never cross because their slopes match; A stays $150 lower. If both F and v match, costs tie at every positive quantity. With A = $80 + $2Q and B = $200 + $5Q, A is lower for every positive Q. With A = $100 + $2.50Q and B = $900 + $2Q, the positive crossing is at 1,600 parts, beyond the live graph's 0–300 interval.
The editable explorer accepts fixed cost $0–$100,000, variable cost $0–$1,000/part and whole demand 1–10,000. Dollar entries have at most two decimal places; exact cent totals determine equality. Displayed average unit costs are approximate. A graph ending before a crossing does not prove there is no crossing. Zero on a total-cost graph shows fixed cost; unit cost at zero parts is undefined.
Static comparison: at 60 parts A is $10.00/part and B is $15.00/part; at 240 parts A is $8.50/part and B is $6.00/part. Use Dimensional Analysis to check units and Outsourcing to consider more than cost.
Materials and Manufacturing Processes/Foundations
Material Utilization and Cost
Check a stock layout, account for cutting loss and roll up material costs.
Prove the parts fit before dividing areas; Practice
Prove the parts fit before dividing areas
Stock is material purchased for further work. Nesting arranges part outlines on stock to reduce waste. An area ratio cannot prove a layout fits. Check dimensions, orientation, grain direction where relevant, edge margins and spacing.
Kerf is the width removed by a cut. An offcut is leftover stock; a usable offcut may be saved. Include trim cuts and holding allowances before promising a part count.
Illustrative layout: a 1,000 mm bar supplies 98 mm blanks. Each blank requires one 2 mm separating cut, including the last blank, with no end trim. Ten blanks consume 10 × (98 + 2) = 1,000 mm. A different last-cut arrangement would need a different cut count.
Test the next-blank threshold; Interactive; Practice
Test the next-blank threshold
Predict first: can the same 1,000 mm stock still supply ten 98 mm blanks if separating kerf increases from 2 to 3 mm? What happens to stock cost per blank when the stock price stays $48?
This one-dimensional lab reserves a full separating kerf after every blank, including the last. Left and right excluded trim lengths already include their own cut losses. The layout does not use the far stock edge as a finished blank edge; it is a count under this policy, not a claim of globally maximum yield.
Usable interval U = stock length L − left excluded trim − right excluded trim Blank count n = floor[U / (blank length b + separating kerf k)]. Round down to a whole number. There are n separating cuts, plus any preparation already accounted for in excluded trim.
Each outlined block is an actual 98 mm blank; the narrow filled band after each is its full 2 mm kerf. Ten blanks plus ten kerfs fill this stock exactly. On narrow screens, scroll sideways to inspect the full bar.
Material balance: 1,000 mm = 0 excluded trim + 980 acceptable blanks + 20 separating kerfs + 0 offcut. Utilization = 980 / 1,000 × 100 = 98.0%.
Change the kerf to 3 mm: ten blanks would need 10 × (98 + 3) = 1,010 mm, so only nine fit. The new balance is 1,000 = 0 + 882 + 27 + 91 mm. The 91 mm offcut is 10 mm short of another 101 mm blank-and-kerf interval.
Allocate the whole stock charge: $48 / 10 = $4.80 per acceptable blank in the original layout; $48 / 9 ≈ $5.33 after the kerf change. All equal-cross-section blanks are assumed acceptable. No remnant credit or processing cost is included. If zero blanks fit, cost per blank is undefined.
Another threshold: at 2 mm kerf, 999.99 mm stock fits nine blanks, while 1,000.00 mm fits ten. This lab uses hundredths of a millimeter and currency cents; its bounded illustrative values are not machine settings. It is not a two-dimensional nesting tool.
Use a consistent physical basis for utilization; Practice
Use a consistent physical basis for utilization
Utilization = material in acceptable parts / material purchased × 100%. Compare length for the same cross-section, area for the same thickness, or mass on a consistent basis.
The bar example gives 980/1,000 × 100 = 98.0%. The remaining 2% is kerf. Distinguish reusable offcuts from material discarded.
Supporting detail: Addendum 99 — Why 20% loss means a 25% increase per useful amount.
Charge each part its share of stock and waste; Practice
Charge each part its share of stock and waste
Part material cost = share of stock charged to the part × stock price. A $48 sheet yielding eight identical acceptable blanks gives $48 × 1/8 = $6.00 per blank when the whole sheet is charged to those blanks. This includes their share of kerf and unusable offcuts.
Finished-part area divided by stock area can understate cost by leaving waste unassigned. State any credit for reusable remnants. Add delivery only if it is not already in the stock price.
A bill of materials (BOM) lists the components and quantities needed for one product. Add quantity × unit cost for every line.
Illustrative material-only BOM
Item
Quantity
Unit cost
Line cost
Blank
2
$6.00
$12.00
Standard fastener
4
$0.25
$1.00
Material total
$13.00
This is not finished product cost. Add processing, assembly and other applicable costs using Manufacturing Cost and Volume.
Materials and Manufacturing Processes/Foundations
Outsourcing
Decide which activities to keep in-house or place with suppliers, weighing relevant costs and capabilities alongside quality, capacity and delivery.
Compare equivalent acceptable parts over the same period
Compare equivalent acceptable parts over the same period
Outsourcing means arranging for an outside supplier to carry out work for the business rather than doing it internally. The work may be making a component or providing a service. A make-or-buy comparison is one application of that broader decision.
A core competence is a capability central to what the business does particularly well. Outsourcing may free resources to focus on those strengths, but it also makes the business depend on suppliers for the work they perform. Compare costs alongside capacity, quality, delivery and capabilities worth retaining. See OpenStax: Outsourcing and core strengths.
Make means produce internally; buy means purchase from a supplier. Define quantity, specifications and delivery date before comparing options. Use Manufacturing Cost and Volume for an initial cost comparison.
Include avoidable setup, tooling, material and processing for make; purchase price, freight, incoming checks and expected rework for buy. Compare costs that change with the decision. Shared rent that remains after outsourcing is not automatically a cash saving.
Start here: decide which future costs change between the two routes, then compare their totals. A relevant cost changes with the choice. An avoidable cost is removed by choosing the other route; a sunk cost has already been incurred and cannot be recovered. Fixed, direct and allocated describe costs, but those labels alone do not establish relevance.
Supporting detail: Addendum 100 — Why the cost boundary matters.
Worked case: which costs change for 100 parts?; Practice
Worked case: which costs change for 100 parts?
This original hypothetical order needs 100 acceptable brackets delivered within one month. All amounts below are illustrative dollars, not supplier prices or facts about a particular shop. For the numeric comparison, assume both routes supply the same specification and acceptable quantity by that deadline.
Making needs a new $300 setup and $9 per acceptable part ($6 material plus $3 additional processing). Buying needs a $10 per-part quote, a separate $0.50 incoming check per part, and $100 freight for the order. The quote excludes those checks and freight. These are future payments incurred only for their respective routes.
The $600 shared rent for the month is paid unchanged either way. A $200 study was paid for last month and is irrecoverable. Assume spare internal capacity, no displaced work or alternative income, and no other route-dependent costs or credits. These are case assumptions; spare time alone does not establish that opportunity cost is zero in a real decision.
Predict before reading the totals: does making's lower per-part charge outweigh its new setup at this quantity? Which two amounts should be excluded from the relevant-cost totals?
Relevant-cost ledger — the same 100 acceptable parts and one-month boundary
Cost and treatment
Make
Buy
New setup: avoidable if buying
$300
$0
Material + additional processing: $9 × 100
$900
$0
Supplier quote: $10 × 100
$0
$1,000
Separate incoming checks: $0.50 × 100
$0
$50
Freight: once per order
$0
$100
Shared rent: $600 either way, excluded
—
—
Past study: $200 irrecoverable, excluded
—
—
Total relevant cost
$1,200
$1,150
Here “—” means excluded from this comparison, not a zero expense. Make = $300 + $900 = $1,200; buy = $1,000 + $50 + $100 = $1,150. Buying is $50 lower under the stated assumptions. The new setup matters even though it is fixed for this order: buying avoids it. Adding the unchanged rent to both sides would leave the $50 difference unchanged; adding it only to make would invent a saving.
For a quantity sensitivity check, use the existing Manufacturing Cost and Volume explorer with A as make ($300 setup, $9/part) and B as buy ($100 order freight, $10.50/part). Identify relevant costs first; the explorer cannot decide which costs belong. Do not add freight or checks again after including them in those inputs.
A cheaper quote can still be the wrong choice; Practice
A cheaper quote can still be the wrong choice
Factor
Question
Capacity
Is machine and staff time available? What other useful work would be displaced?
Quality
Can each route meet the specification consistently, and how will it be verified?
Lead time
Can the route deliver when needed, including queues and transport?
Core competence
Is this capability central to what the organization does well and needs to retain?
Risk
What happens if demand changes, a supplier fails or the design changes?
Standard parts often favor buying; distinctive capabilities may favor making. Neither is a rule based on volume alone.
The worked case establishes a conditional cost difference. It does not verify a supplier's quality, available capacity or delivery promise. Before committing, obtain evidence that each route can meet the requirement. If making displaces another useful job, include the benefit given up; if buying adds rework, expediting or other costs, revise the ledger. See OpenStax: Make or buy a component for avoidable fixed costs and the qualitative checks alongside the numeric analysis.
Make the required function easier to produce, assemble, inspect and maintain.
Keep the function and simplify how it is made
Keep the function and simplify how it is made
Design for manufacturing (DFM) considers production while a design can still change. Preserve required strength, fit and service performance; remove complexity that serves no requirement.
Reduce separate parts when this simplifies production and service.
Use standard components and available stock sizes.
Match geometry to the process and provide tool and inspection access.
Make assembly easy to orient, reach and verify.
Fewer parts can reduce joining work, but one complex part may need costly tooling or be hard to repair. Compare the whole route.
Specify only the precision the function needs
Specify only the precision the function needs
A tolerance is the allowed variation in a dimension or other feature. Tight tolerances may require careful setups, slower processing and more capable inspection. Keep tight control where fit or function needs it; do not apply it everywhere by habit.
No machine name guarantees a tolerance or price. Geometry, material, tooling, setup and measurement all matter. Confirm capability for the actual feature.
Supporting detail: Addendum 101 — Why the loosest tolerance is not automatically cheapest.
Reduce material loss without shortening useful life; Checklist
Reduce material loss without shortening useful life
Use Material Utilization and Cost to compare layouts. Also consider energy, durability, repair, disassembly and practical material recovery at end of life. A lighter part that fails early may consume more resources over its service life.
Identify each part's function and critical features.
Check standard components and stock sizes.
Sketch manufacturing, assembly and inspection access.
Check tolerances against function and process capability.
Compare material use, service life and repair or recycling options.
Lean and Quality/Continuous Improvement
Lean Value and Flow
Define customer value and improve the whole path from request to delivery.
Start with what the customer needs
Start with what the customer needs
Lean thinking improves how work creates value while reducing waste and respecting the people doing it. Value is judged from the customer's need: the right function and quality, in the needed quantity, at the needed time.
A busy machine is not proof of useful output. Making something early that nobody needs can increase storage and delay the work that is needed.
Separate value creation from necessary support and avoidable waste
Separate value creation from necessary support and avoidable waste
Value-added work changes the product or service toward the customer's requirement and is done correctly. Cutting a needed feature may add value; searching for a misplaced tool does not.
Some non-value-added work is currently necessary: required checks, safety measures and records protect customers and workers. Improve how that work is done; do not delete a safeguard because it does not physically change the product.
Supporting detail: Addendum 102 — Process time is not automatically value-added time.
5S Workplace Organization supports visible, repeatable work. It is one supporting method, not the whole of lean.
Lean and Quality/Continuous Improvement
Eight Wastes: TIMWOODS
Recognize eight patterns of wasted effort in manufacturing and daily life.
Use TIMWOODS to name what you observe
Use TIMWOODS to name what you observe
Transportation, Inventory, Motion, Waiting, Overproduction, Over-processing, Defects and Skills form TIMWOODS. Describe the observed problem before choosing a remedy.
Compare shop examples with everyday examples
Compare shop examples with everyday examples
These are illustrative examples, not descriptions of a particular shop.
Transportation: unnecessary material movement
Shop: A part travels to a distant holding area and back. Daily life: Moving stored boxes between rooms without using them.
Inventory: excess material or work
Shop: Unneeded blanks fill a rack. Daily life: Buying food that expires before use.
Motion: unnecessary movement by people
Shop: An operator searches several drawers for a tool. Daily life: Searching for misplaced keys.
Waiting: idle time before work can proceed
Shop: A prepared job waits for missing information. Daily life: A completed form sits awaiting approval.
Overproduction: too much or too early
Shop: Extra parts are made without demand. Daily life: Printing copies nobody requested.
Over-processing: work beyond requirements
Shop: A hidden face receives an unnecessary cosmetic finish. Daily life: Entering the same information into duplicate lists.
Defects: work that fails requirements
Shop: An incorrect hole pattern requires a replacement part. Daily life: Retyping a form because of incorrect entries.
Skills: unused talent
Shop: An experienced operator's improvement idea is never considered. Daily life: Ignoring a team member's relevant skill when dividing work.
Distinguish similar wastes before proposing a change; Practice
Distinguish similar wastes before proposing a change
Transportation follows material; motion follows people. Overproduction creates unwanted output; inventory is the resulting excess stock. Several wastes can occur together.
Inspection is not automatically a defect, and every machine cycle is not automatically wasted time. Check Lean Value and Flow. Buffers may be needed for supply variation; removing them without understanding demand and reliability can interrupt delivery.
Show material and information flow, then distinguish process time from elapsed lead time.
Map one product family from request to delivery
Map one product family from request to delivery
A value stream map (VSM) shows the steps and information that move a product or service toward the customer. Define the boundary and select work following a similar route. Walk the current process and record what happens, including queues and handoffs.
Show who requests work, how instructions reach production, where material moves and where it waits. An operations-only map misses the information controlling those operations.
Read process boxes, inventory triangles and flow arrows
Read process boxes, inventory triangles and flow arrows
This original sketch uses common conventions: a rectangle for a process, a triangle marked I for inventory, attached data boxes for measurements and arrows for flow. The legend distinguishes material movement from information. This is a teaching sketch, not a complete symbol standard.
Measure elapsed lead time separately from process time; Interactive; Practice
Measure elapsed lead time separately from process time
Lead time is elapsed time through the stated boundary, including waits. Process time is time actively spent doing the work within that boundary. Not all processing adds customer value.
Transfer size changes when jobs finish
10 jobs; A = 4 min/job, B = 6 min/job. Compare transfer-all with transfer-one.
Transfer all 10 jobs
First item 46 minFull order 100 minProcessing / job 10 min
Transfer 1 at a time
First item 10 minFull order 64 minProcessing / job 10 min
A is upper blue, B lower gold; bars are jobs, dashed lines completed-batch transfers. Minutes from order release 0; both plots share a scale.
Job 10 with transfer-one: 36 min waiting before A + 0 held for batch + 18 waiting at B = 54 min waiting. Add 10 min processing: 64 min elapsed from order release 0.
Ideal schedule: all equal jobs arrive at 0; serial single-job A then B, first come first served. A never blocks; waiting space is unlimited. Completed batches transfer immediately; the last may be smaller. Constant times; no setup, transport, failure, rework or variation. Finite-order illustration, not a factory forecast or a universal best batch.
Supporting detail: Addendum 104 — Bounded model reference: scheduling equations and limits.
The transfer-batch experiment above schedules a whole order. The earlier map sketch uses a fixed queue for one item:
For one item in this simplified sequential example: cutting = 4 min, queue = 120 min, assembly = 6 min. Process time is 10 min; lead time is 130 min. No other delays or overlapping steps are included. Removing half the queue saves more elapsed time here than cutting one minute of processing.
Supporting detail: Addendum 105 — A queue suggests a question, not a proven cause.
A future-state map describes an improved flow to work toward. Choose a measurable change, assign responsibility and check the effect using Kaizen and Standard Work. Compare delivery, quality and workload across the whole stream.
Lean and Quality/Continuous Improvement
Kaizen and Standard Work
Use small measured experiments to improve work and preserve what the team learns.
Improve a specific problem with the people doing the work
Improve a specific problem with the people doing the work
Kaizen means continuous improvement. Start with an observed problem and a small change whose effect can be checked. Invite the people performing the task to explain what makes it difficult.
For example, repeated searching for a shared measuring tool may suggest a labeled location. Measure search time and check whether the location also works for the next user. This is an illustrative experiment, not a promised productivity gain.
Use Plan–Do–Check–Act to learn from a change
Use Plan–Do–Check–Act to learn from a change
Plan: define the problem, measure the starting condition and predict the effect of a proposed change.
Do: try an authorized change on a manageable scale and record what happens.
Check: compare results with the prediction, including quality and unintended effects.
Act: adopt and document an improvement, revise an uncertain idea or undo an unsuccessful change; begin the next cycle.
A useful result may be that the idea did not help. Keep that evidence rather than declaring success because something changed.
Use standard work as a baseline that can improve; Checklist
Use standard work as a baseline that can improve
Standard work records the current agreed method so people can repeat it and recognize departures. State the sequence, relevant timing, checks and materials needed. In repetitive production, standardized work also relates the sequence and required in-process stock to the pace of customer demand.
When an improvement is demonstrated, update the method and help everyone learn it. Do not bypass safety requirements or change controlled specifications as an informal experiment.
Record the problem and starting measure.
Describe one change and the expected result.
Test within applicable authorization and safety requirements.
Compare results and effects on other people or steps.
Update the agreed method if the evidence supports the change.
Addendum 1. “It’s not the voltage that gets you, it’s the current”
The saying is true. What usually gets taken from it — that the voltage does not matter
— is not. Current is electricity actually moving through you, and it takes very little of
it to do real harm. Volts sitting on a wire nobody is touching do nothing at all.
Two things together decide how much current you get: how hard the electricity is being pushed,
which is what voltage measures, and how hard your body holds it back, which is called resistance.
Harder push, more current. More resistance, less.
Your resistance is not a fixed number — wet skin holds current back far less than dry
skin does, so the same push moves much more current through you. That half of it cannot be relied
on, which is why the line is drawn on the half that can be: the push.
Addendum 2. The international standards are not one number
On datasheets you will meet a different set of figures, and there the AC and DC limits
are not the same:
50 V AC / 120 V DC
Extra-Low Voltage under
IEC 61140 and IEC 60364-4-41 — 50 V AC rms, or 120 V
ripple-free DC. “Ripple-free” is a real condition, not a figure of speech:
past roughly 10 % rms ripple the supply is treated as AC and the lower number applies.
30 V AC / 60 V DC
Class ES1 in IEC 62368-1, the
standard behind most benchtop and consumer equipment. ES1 is the class that needs no safeguard
at all; ES2 runs up to 50 V AC / 120 V DC and requires one.
Addendum 3. All sixteen sections, and the four OSHA does not enforce
This is OSHA's own list, from Appendix D to 29 CFR 1910.1200. The numbers
and headings are fixed; a manufacturer cannot renumber them or reorder them.
Section 1
Identification — product identifier, recommended use and
restrictions on use, who made it, emergency phone number.
Section 2
Hazard(s) identification — classification, signal word,
hazard statement(s), symbol(s) and precautionary statement(s).
Section 3
Composition / information on ingredients — chemical name,
CAS number, and for a mixture, the ingredients classified as health hazards and how much of
each.
Section 4
First-aid measures — by route of exposure, plus the symptoms
that matter and when to get medical attention.
Section 5
Fire-fighting measures — suitable and unsuitable
extinguishing media, and what the chemical gives off when it burns.
Section 6
Accidental release measures — the spill response.
Section 7
Handling and storage — "conditions for safe storage,
including any incompatibilities".
Section 8
Exposure controls / personal protection — the OSHA
permissible exposure limit, the ACGIH threshold limit value, engineering controls, PPE.
Section 9
Physical and chemical properties — physical state, odor,
flash point, auto-ignition temperature, density, pH and the rest.
Section 10
Stability and reactivity — reactivity, conditions to avoid,
"incompatible materials", hazardous decomposition products.
Section 11
Toxicological information — the health effects and the data
behind them, including any carcinogen listings.
Section 12
Ecological information
Section 13
Disposal considerations
Section 14
Transport information
Section 15
Regulatory information
Section 16
Other information — "the date of preparation of the SDS
or the last change to it".
Twelve through fifteen are the odd ones out.
The headings have to be there: a note to the standard says an SDS "must also include the
headings" for those four, "in order", to stay consistent with the international
system the format comes from. What goes under them is a different question. Appendix D
says "Sections 12-15 may be included in the SDS, but are not mandatory", and a second
note to the same paragraph says "OSHA will not be enforcing information requirements in
sections 12 through 15, as these areas are not under its jurisdiction."
Those four cover the environment, waste, shipping and other agencies' regulations —
EPA and DOT ground, not OSHA's. So Section 13 tells you what the manufacturer suggests doing
with the leftovers. It does not tell you what happens to them here. Ask.
Two more things about the shape of the document. The section order is fixed
but the order within a section is not — preparers "are not required to
present the information in any particular order within each section", so two sheets can
look different inside the same numbered box. And a heading with nothing under it is not an
oversight: where there is no relevant information, "the SDS shall clearly indicate that no
applicable information is available." Read that as nobody has the data — not as
nothing to worry about.
Addendum 4. Signal words, pictograms and H-numbers — how Section 2 is written
There are exactly two signal words, and OSHA defines them in
1910.1200(c): a signal word indicates "the relative level of severity of
hazard", and "'Danger' is used for the more severe hazards, while 'warning' is used
for the less severe."
Severity is relative to the same kind of hazard, and that is the part that catches
people. Flammable liquids in OSHA's Appendix C are the clean example — all three
categories carry the same Flame pictogram, and the signal word is the only
thing separating them:
Category 1
Danger — "Extremely flammable liquid and vapor"
Category 2
Danger — "Highly flammable liquid and vapor"
Category 3
Warning — "Flammable liquid and vapor"
So “warning” does not mean mild. A Category 3
flammable liquid still catches fire. The signal word ranks a hazard against others of its own
kind; it is not a statement that the chemical is safe.
The pictograms are a fixed set of eight — a black symbol in a
red-bordered diamond standing on a point. OSHA names them: Flame, Flame Over Circle,
Exclamation Mark, Exploding Bomb, Corrosion, Gas Cylinder, Health Hazard, and Skull and
Crossbones.
The eight OSHA Hazard Communication pictograms
Flame
Flame Over Circle
Exclamation Mark
Exploding Bomb
Corrosion
Gas Cylinder
Health Hazard
Skull and Crossbones
The H-numbers are an index, not the warning. Real sheets often print a code
such as H225 beside a hazard statement. Those codes come from the international GHS
scheme this format is built on, which treats them as reference labels rather than as a
substitute for the statement itself. OSHA's Appendix C does not use them at all — it
specifies the sentence. Read the sentence.
Addendum 5. Telling a current sheet from an old one
Section 16 carries "the date of preparation of the SDS or the last
change to it." That is the only date on the document, and it is how you tell a live sheet
from one that has sat in a binder for a decade.
Keeping it current is the manufacturer's job, not yours. Under
1910.1200(g)(5), when a manufacturer or importer "becomes newly aware of
any significant information regarding the hazards of a chemical, or ways to protect against the
hazards, this new information shall be added to the safety data sheet within three
months."
Addendum 6. What makes a flammables cabinet “approved”, and how to spot one
OSHA calls it a storage cabinet and defines it by a fire test rather than by
how solid it looks. 29 CFR 1910.106(d)(3) requires cabinets to "limit the
internal temperature to not more than 325 °F. when subjected to a 10-minute fire test",
with all joints and seams staying tight and the door staying closed throughout.
The same paragraph requires the marking, which is the fastest way to recognise one:
"Cabinets shall be labeled in conspicuous lettering, 'Flammable - Keep Fire Away.'"
Addendum 7. The word for this, and where it comes from
“Nip point” is not shop slang. It is the term the machine-guarding standard uses.
29 CFR 1910.212(a)(1) requires guarding against “hazards such as
those created by point of operation, ingoing nip points, rotating parts, flying chips and
sparks.”
OSHA’s Machine Guarding eTool puts it plainly: “In-running nip point
hazards are caused by the rotating parts on machinery.” Its longer treatment,
Concepts and Techniques of Machine Safeguarding (OSHA 3067), gives three kinds:
“Parts can rotate in opposite directions while their axes are parallel to each other.
These parts may be in contact (producing a nip point) or in close proximity.” —
meshing gears.
“Nip points are also created between rotating and tangentially moving parts. Some
examples would be: the point of contact between a power transmission belt and its pulley, a
chain and a sprocket, and a rack and pinion.”
“Nip points can occur between rotating and fixed parts which create a shearing,
crushing, or abrading action.”
So belts, chains, sprockets and gears are rotating hazards by name. What makes them
dangerous is that they draw material in — not that two parts close on each other.
OSHA is just as direct about the plain shaft: “Rotating motion can be dangerous; even
smooth, slowly rotating shafts can grip hair and clothing, and through minor contact force the
hand and arm into a dangerous position.”
These parts are meant to be behind covers, and the standard is specific about it —
29 CFR 1910.219(f)(3): “All sprocket wheels and chains shall be
enclosed unless they are more than seven (7) feet above the floor or platform.”
Addendum 8. What the investigations actually describe
Oregon’s state fatality-investigation program, summarizing the record for this class of
machine: “The most common causes of death and injury from metal lathes include
entanglement of clothing in moving parts, being hit by loose objects on the lathe (e.g.,
chuck keys, tools, metal shavings) and being struck by a part that has not been adequately
secured.” (OR-FACE 2012-18-1, Experienced Journeyman Machinist Killed While
Operating an Engine Lathe, 2014.)
Four investigated deaths, all the same event — something attached to a person touched
something turning, and the machine did the rest:
Smoothing a part while it turned. A 69-year-old machinist with over 30
years’ experience “reached over the work piece to smooth out a radiused transition
with emery cloth and a file in hand” and “his loose clothing (left arm sleeve)
became entangled around the rotating work piece”. A co-worker 30 feet away heard “a
strange ‘winding-up’ sound”. Of that same part, the shop foreman had said that
“the rough surface could grab clothing or gloves”. (OR-FACE 2012-18-1.)
Stock sticking out the back of the spindle. A 52-year-old machinist was
set up on a 103-inch steel bar: “Due to the length of the material, 24 inches were
sticking out the back of the lathe, unguarded, and held in place with a clamping device that
rotates as the lathe rotates.” He reached across the running machine and “the sleeve
of his shirt became entangled”. (Kentucky FACE 21KY002, 2021.)
A burr on the end of the bar. A lathe operator in his twenties had a
1 7/8-inch stub of 1-inch bar standing past the tailstock. “The right pocket of his
shirt was caught by the rotating tailstock burr. His shirt wrapped around the stock and
tightened at the decedent’s neck and chest.” The listed contributing factor is
“walking to and/or reaching over unguarded rotating bar stock”. OSHA makes the same
point in general: the danger “increases when projections such as set screws, bolts, nicks,
abrasions, and projecting keys… are exposed on rotating parts.”
(Michigan FACE 14MI034, 2014; OSHA Machine Guarding eTool.)
A drill press. “As Employee #1 reached into the unguarded point
of operation, his shirt sleeve or gloves became entangled in the drill bit. Employee #1 was
pulled toward the machine, entangling Employee #1’s long hair. The drill press
continued to spin, completely pulling Employee #1 into the operating area.” She died
of her injuries. The same report records that the spindle “had speeds that ranged from 45
to 1115 rotations per minute”. (OSHA accident 114097.015, 20 February 2019.)
Why abrasive cloth keeps appearing. The UK Health and Safety Executive
publishes a sheet on this one task: “Every year there are serious accidents involving the
use of emery cloth on metalworking lathes. These accidents result in serious injuries such as
broken bones, dislocations, lacerations, amputations and occasionally death.” The mechanism
it names is the one above: “Accidents occur when hand-held emery cloth is entangled in the
rotating parts of the machine or where the emery cloth is snagged on the rotating component
dragging the operator into the danger zone.” Its own rules are that emery
cloth “should NEVER be applied directly by hand on manual metalworking lathes”, and
that gloves “increase the risk of entanglement and” are “never acceptable near
rotating parts of machinery”. (HSE Engineering Information Sheet No 2, rev 1,
2015 — that is HSE’s guidance; ask what the procedure is in the shop you are
standing in.)
And the drill press is not the exception it looks like. OSHA’s own
drill-press training script lists, among the ways accidents happen, “getting dangling
jewelry, loose clothing, or hair caught in the drill chuck (rotational hazard)”, and states:
“The primary hazards of drill presses are contact at the point of operation and
rotational hazards. An operator can risk serious hand injury when working too
close to the drilling area, wearing gloves, loose clothing, loose hair, or jewelry.”
Addendum 9. Why belts and chains count as rotating, not pinching
OSHA sorts machine hazards by the motion that causes them, and “pinch point” is
the vocabulary it attaches to parts that travel, not to parts that turn. From
Concepts and Techniques of Machine Safeguarding (OSHA 3067):
Reciprocating motion — “Reciprocating motions may be hazardous
because, during the back-and-forth or up-and-down motion, a worker may be struck by or caught
between a moving and a stationary part.”
Transverse motion, which means movement in a straight continuous line
— “Transverse motion (movement in a straight, continuous line) creates a hazard
because a worker may be struck or caught in a pinch or shear point by the
moving part.”
A belt on a pulley is a rotating hazard that draws material in; a table running up against a
column is a moving hazard that closes on it. Both can take a hand, and the vocabulary is worth
keeping straight because the two do not have the same tell. You avoid the first
by giving it nothing to grip. You avoid the second by knowing where the gap is going.
Guarding is not a local preference. 29 CFR 1910.212(a)(1) —
quoted already in Rotating machinery above for its definition of a nip point — is
a guarding requirement first: one or more methods of machine guarding shall be provided to
protect the operator and other employees from hazards including those created by point of
operation, ingoing nip points, rotating parts, flying chips and sparks.
The reason a rule like this is written without exceptions is that the exceptions are exactly
where people get hurt. A guard comes off for a legitimate setup, the setup takes longer than
expected, somebody else walks up to a machine that looks normal and is not. The standard's own
answer to “but this task genuinely needs the guard off” is not a more
careful operator — it is Lockout/Tagout, the next card on this page, which is
a procedure rather than a permission.
29 CFR 1910.147(a)(1)(i): “This standard covers the servicing
and maintenance of machines and equipment in which the unexpected energization or start
up of the machines or equipment, or release of stored energy could cause injury
to employees.”
Two things are worth reading twice. Unexpected is the whole point — the
hazard is not that the machine runs, it is that it runs while someone has a hand inside it. And
stored energy is named alongside energization, because a machine that has been
switched off and unplugged can still contain everything it needs to move once.
“Servicing and maintenance” is much broader than it sounds. The standard defines it
as “constructing, installing, setting up, adjusting, inspecting, modifying, and
maintaining and/or servicing machines or equipment”, and adds: “These
activities include lubrication, cleaning or unjamming of machines or equipment
and making adjustments or tool changes, where the employee may be exposed to the
unexpected energization or startup of the equipment or release of hazardous energy.” Setting
up, clearing a jam and changing a tool are all on that list.
Stored energy gets its own requirement — 1910.147(d)(5)(i):
“Following the application of lockout or tagout devices to energy isolating devices, all
potentially hazardous stored or residual energy shall be relieved, disconnected, restrained, and
otherwise rendered safe.” The lock comes first, and then the energy already in the machine
is dealt with. Both, in that order.
Addendum 12. Why the chuck key rule is worded as a grip and not as a reminder
A key left in a chuck is launched the instant the machine starts. Written as
“remember to remove the key” the rule depends on you remembering at the one
moment you are busy with something else; written as the key never leaves your hand there
is nothing to remember, because a key that is still in the chuck is still in your hand and you
cannot start the machine.
Do not let a spring be the thing that saves you. Some chuck keys are
spring-loaded and eject themselves when you let go — ours are, on the lathe. Not all keys
are, and our Jacobs chuck keys are not. So the habit has to be the same on every
machine, or it is a habit that works until you walk up to a different chuck.
A drill-press chuck key is lighter than a lathe chuck key and carries far less energy. It is
still dangerous: it is in the list of things that become projectiles in Rotating
machinery above, and “less mass” is not the same as “will not hurt you”
when it leaves a spinning chuck at the distance you are standing.
Addendum 13. Why dry sand is on the list, and why it is probably not on yours
Sand does work. The Aluminum Association’s Guidelines for Handling Aluminum
Fines (F-1) lists fine dry sand, “preferably finer than 20 mesh,” next to
approved dry powders as effective for isolating an aluminum fines fire. It also says
what has to be true first.
Dry. F-1 says dry sand. Damp sand is water, and water
“will react with the aluminum fines to form flammable hydrogen gas.”
Already in the room. “A plentiful supply should be easily available
in the operating area and stored in covered bins or drums.” Sand fetched after the fire
starts is not that.
With the right tool waiting beside it. “Long handled shovels should
be available at each bin or drum, and should be constructed of non-sparking metal.”
Laid, not thrown. The shovels “lay the sand or powder around the
edge or perimeter of the fire.” You are walling it in. Anything thrown at the pile
raises the dust cloud that is the actual explosion.
Decided before it started, by someone senior. “Qualified
supervisory personnel should decide in advance whether it is better to attempt to fight the
fire or to withdraw to a safe location and allow it to burn itself out.”
Those are preconditions, not tips. If you cannot point at the covered sand bin and
the non-sparking shovel beside it right now, you do not have this option — and
the call to fight it was never yours to make on the spot. Alarm, evacuate, report.
Addendum 14. Why one feed rate does not fit every cut
Thickness, wood, blade and available power change how readily material cuts. Pushing harder does not fix binding or a poorly chosen setup; it can make control worse.
Addendum 15. Why thickness matters as well as material
A thin section needs enough teeth engaged to avoid snagging; a thick section also needs room between teeth to carry chips away. Select the blade for both conditions rather than assuming all metal needs the same high TPI.
Addendum 16. Why larger drills usually need fewer revolutions per minute
At the same spindle speed, a larger bit's outer edge travels faster. Diameter, work material and bit material all affect the speed choice. “Larger or harder means slower” is a starting trend, not a speed setting.
Different industries draw the primary/secondary boundary differently. Here, use the raw-resource-to-stock and stock-to-part distinction. Extraction supplies the raw resource; mining alone does not turn ore into an ingot. A supplier's finished product can also be the next manufacturer's starting material.
Addendum 18. A laser cut does not have to vaporize all the removed material
Material may melt and be expelled from the cut; vaporization can also contribute. The classification depends on removal, not on which thermal mechanism dominates. TWI explains melt removal in laser cutting.
Addendum 19. Why another book may show a different family list
Other books may give composites a separate family, split glass from ceramics, or organize materials by bonding and structure. This collection keeps the instructor's four-family model. Engineered composites belong within Wood & Composites, including composites with no wood in them.
Some materials fit more than one description. In the course's examples, plain concrete sits with Ceramics & Glass; steel-reinforced concrete illustrates Wood & Composites when the combined material system is the subject. Concrete itself also has a composite structure. State what is being classified rather than treating these labels as mutually exclusive scientific definitions.
Addendum 20. A supplier value that checks the floating claim
Plaskolite's OPTIX acrylic data lists a relative density of 1.19, with water as the comparison. This supports the conclusion that a solid piece is denser than water. Family descriptions are screening guides; use the actual grade's data for a design.
Addendum 21. Hard to machine does not mean impossible to machine
Corning's MACOR glass-ceramic is specifically designed for machining with conventional metalworking tools. That is a useful counterexample to a blanket claim that ceramics cannot be worked after forming.
Addendum 22. Stress, strain and modulus give the comparison units
For a simple axial test, engineering stress is force divided by original cross-sectional area. Engineering strain is change in length divided by original length. Stress has units such as MPa; strain is a ratio with no unit.
In a linear elastic region, the slope of stress against strain is Young's modulus, a measure of material stiffness. Yield strength concerns permanent deformation; ultimate tensile strength is the highest engineering tensile stress reached in the test. A nonlinear curve does not, by itself, prove that a material has no yield behavior.
Addendum 23. Why a single “toughness number” needs its test method
The area under a tensile stress–strain curve through fracture measures energy absorbed per original volume in that test. Impact tests and fracture-toughness tests describe related but different behavior. Temperature, loading rate and flaws can change the result, so compare like tests.
Addendum 24. Not every material has one useful melting-point number
Pure crystalline substances can have a sharp melting point; many alloys melt over a range. Glass and amorphous thermoplastics soften over a range rather than showing a sharp crystalline melting transition. Thermosets and wood decompose rather than melting into a reusable processing liquid. Use material-specific processing and service data.
Addendum 25. Vocabulary, brand attribution and source scope
ISO/ASTM 52900:2021 is the current fundamentals-and-vocabulary standard and describes additive shaping as successive addition of material. Its public abstract does not reproduce the full family list. The family structure and readable mechanisms here are checked against the NIST AM technology overview and the seven-family discussion in ORNL's Additive Manufacturing Design Guidelines. Stratasys's legal terms identify FDM as a registered trademark and PolyJet as a trademark; its PolyJet technology page documents the bounded photopolymer-droplet, UV-cure and support example used here. This page paraphrases sources and uses original graphics rather than copied standard or vendor art.
Addendum 27. Why the support statement is qualified
Ohio State's laser-PBF research summary explains support structures used to anchor overhangs and address thermally induced distortion in that context. A current Colibrium EB-PBF example documents process strategies that reduce or eliminate traditional supports for some applications. The exception is why this page states a case rather than an absolute.
Addendum 28. Softening, melting and heat resistance are different questions
Some thermoplastics soften over a range rather than having one sharp melting temperature. A part can lose stiffness and fail under load well before it flows. Thermosets also have service-temperature limits: being unable to remelt does not make them heatproof. Use the grade's data sheet for the actual load and temperature.
Addendum 29. Why a short strength test does not settle a long service life
Temperature, time, moisture and chemicals can change both dimensions and load-carrying ability. A part that survives a brief pull may still creep over months. Curbell's dimensional-stability guide connects these effects to material selection.
Addendum 31. Where the resin comparison comes from
The American Composites Manufacturers Association guide, Appendix D, compares composite resin systems. The resin holds and transfers load between the reinforcing fibers; the fibers and their orientation strongly affect the resulting composite.
The number-to-material matches are published in the City of Sioux Falls RIC guide. The PET Resin Association consumer guide supplies the familiar label terminology. Checked October 27, 2026. This is an identification reference, not a specification for manufacturing compliant labels.
A shallow depression opposite a heavy rib suggests sink.
Scraping during release suggests inadequate draft or another ejection problem.
A sudden thick-to-thin step suggests uneven cooling and difficult filling.
Protolabs' defect guide illustrates these relationships. Wall and draft requirements depend on resin, texture, depth and tooling; no single angle or thickness fits every part.
Addendum 42. Find the quantity where the two estimates are equal
Set total costs equal: 900 + 14N = 18000 + 2N. Then 12N = 17100, so N = 1,425 parts. Below that quantity A costs less; above it B costs less under these assumptions.
This model leaves out financing, mold replacement, setup changes, inspection, shipping and rejects. A flexible mold that must be replaced during a run adds another tooling cost. Recalculate when the assumptions change.
Addendum 44. Why a slower cut can produce more heat
A tooth that advances too little spends more time sliding against the work. The next tooth may also recut trapped chips. Useful chips carry some heat away, so reducing chip thickness without reducing rubbing is not a reliable cooling strategy. ACRYLITE's drilling guidance identifies low feed or excessive RPM as causes of melted chips; its routing guidance treats feed, cutting edges and RPM together.
Addendum 46. Why a clean-looking bond can peel off
The bond is only as good as the material it touches. Mold-release residue, oil or an unsuitable coating can become the weak layer. Peel loads concentrate force at an edge; an overlapping joint can distribute load more effectively, although its dimensions still need validation. 3M explains low surface energy, and its bonding guidance shows why PE and PP are difficult, rather than impossible, to bond.
Addendum 47. Why heat alone does not guarantee a strong or sealed weld
Temperature, force, time and joint fit work together. Too little heating leaves an unfused interface; excessive heating can degrade the polymer. Ultrasonic joints often use a small molded ridge, an energy director, to concentrate heating. A continuous-looking bead does not prove a leak-tight seam. Leister's extrusion-welding guidance identifies matching filler and joint geometry; Dukane's Guide to Ultrasonic Plastics Assembly explains energy directors for ultrasonic welding.
Addendum 48. Insert dimensions come from the chosen insert system
SPIROL's hole-design guidance explains how oversized holes reduce performance and undersized holes can introduce stress or cracks. Its insert design guide distinguishes heat-installed thermoplastic inserts from other installation methods.
Materials and Manufacturing Processes/Plastics/FDM 3D Printing
Addendum 49. Where additive manufacturing fits the five course categories
This course uses purpose to choose a primary category. Additive shape-building is Forming because creating the shape is the intended result; bonding between deposited roads is a secondary fabricating effect rather than joining previously separate parts. Other technical taxonomies organize these processes differently. The standard AM family name here is material extrusion. Subsequent support removal is Separating; annealing is Conditioning; sanding or painting is Finishing.
Materials and Manufacturing Processes/Plastics/FDM 3D Printing
Addendum 50. Material guidance is grade-specific
Filament names describe families, not identical recipes. Pigments, fillers and blends change behavior. Prusa's material guide separates common filament families and their printing requirements. It does not establish what any particular shop printer can process.
Addendum 51. Stress relief and crystallinity are different changes
Residual stress is locked-in stress remaining after manufacturing. Heating can allow molecular motion that relaxes it. Some polymers, including PLA, can also develop more ordered regions during suitable heat treatment. Acrylic stress relief and PLA crystallization therefore do not share a universal temperature recipe. ACRYLITE's annealing guidance describes stress relief for its sheet. Prusa's annealing experiments show why dimensional change must be checked on printed specimens.
Addendum 52. Other ways processors change plastic properties
Industrial radiation treatment can crosslink selected polymers, but the result depends on the polymer and dose; some systems also undergo chain breakdown. Additives and reinforcements usually enter during material formulation rather than as a finishing step on a completed part. Fibers can increase stiffness, meaning a higher elastic modulus in the relevant direction, not a lower one. These changes require grade-specific data.
Surface treatment can leave stress or expose existing stress to a solvent. Fine cracks may appear during later cleaning or bonding. ACRYLITE's edge-finishing guidance discusses polishing and compatibility; Prusa's ABS guidance identifies acetone smoothing for ABS. Choose a verified material/process pair, then check both appearance and fit.
Addendum 54. Powder coating needs a complete substrate and cure system
Interpon's heat-sensitive-substrate overview distinguishes powder-coating systems for heat-sensitive substrates, including thermal and UV curing approaches. A conventional metal-part powder cure is not a default recipe for a plastic part.
Addendum 55. What makes the cell walls work together?
Cellulose reinforces the cell wall, while lignin and hemicelluloses help form its surrounding structure. This is a useful natural-composite analogy, but a tree is more complex than fibers suspended in glue. Cell arrangement, moisture, knots, and grain direction all affect a real board.
Most commercial hardwoods have vessels, visible as pores in end grain, along with supporting fibers. Softwoods rely mainly on long cells called tracheids for support and water transport. These differences influence appearance and processing, but do not make every member of either group behave alike.
Addendum 59. Why the mixed-unit formula divides by 12
Convert the length in feet to inches by multiplying by 12. Dividing the resulting cubic inches by 144 gives 12/144 = 1/12. The formula counts 144-cubic-inch units; it is not a linear-foot conversion.
Addendum 62. Why tooth geometry changes the surface
Across the grain, fibers can break beyond the intended cut if they are pushed away before being severed. Beveled teeth help slice those fibers. Along the grain, chip removal is a major concern. A blade's tooth shape, spacing, sharpness and feed all affect the result; tooth count alone does not identify its job.
Ridge Carbide Tool's saw-blade design glossary defines gullet, kerf and hook angle; its top-grind guide compares tooth shapes. Choose a blade specified for the machine and cutting application.
Addendum 64. Why “router bit” is more useful than “end mill” here
CNC routing can use end-mill-like spiral cutters, but routing also includes bearing-guided and shaped profile bits. “End mill” alone does not describe the tooling a beginning woodworker will encounter. Whiteside's template-bit range illustrates tooling for following patterns; its catalog also includes straight bits, flush-trim spiral bits and roundover profiles.
Addendum 65. Why a planer alone can preserve a bow
Feed rollers can press a bowed board flatter during the cut. When the pressure is released, the board can spring back. Uniform thickness and flatness are different requirements. Specialized fixtures can provide a reference for other methods, but the sequence here assumes an ordinary jointer and thickness planer.
Moisture lowers the temperature at which the wood's matrix softens. This is why moist heat can make wood bendable without melting it. The USDA Forest Products Laboratory's Wood Handbook chapter on specialty treatments discusses plasticizing wood. Its Bending Solid Wood to Form compares species and bending conditions.
Addendum 67. Why the indoor moisture target depends on the building
The handbook's interior recommendations were developed from well-ventilated buildings without unusual moisture sources or air conditioning. Air conditioning and other building conditions can change the appropriate target. These are installation guidelines, not a universal kiln-drying specification; see Recommended Moisture Content, page 13–3.
Addendum 68. Why dividing by the initial mass answers a different question
30 / 230 × 100 = 13.0% gives the water fraction of the initial sample, not wood moisture content on the oven-dry basis. Wood MC can exceed 100% when water mass exceeds dry wood mass. The calculation does not set a suitable target for furniture. An actual oven-dry determination requires an appropriate laboratory method and equipment; these exercises provide the dry mass.
Addendum 69. What “stronger than the wood” actually demonstrates
In a well-made joint tested under a particular load, failure may occur in the surrounding wood rather than at the bond line. That shows the bond outlasted that wood under those conditions. It does not show that every adhesive joint exceeds every strength of wood, or that an end-grain butt joint is as strong as an uncut member. Grain direction, stress type, moisture, temperature and time under load can change the result.
Addendum 71. Further product-specific preparation guidance
General Finishes' wood preparation guide is a starting point for that manufacturer's systems. Use the exact product's current instructions to choose the final grit and recoat schedule.
Addendum 72. Why two pieces of the same alloy can behave differently
Permanent deformation involves movement of crystal defects called dislocations. Grain boundaries, dissolved alloying atoms and small particles can obstruct that movement. Cold working and heat treatment change these obstacles. Composition alone therefore cannot tell you the strength of a finished piece.
Addendum 73. Why connecting two different metals can change corrosion
When dissimilar metals are electrically connected in a conducting liquid, such as salty water, galvanic corrosion can accelerate attack on the more active metal. Material pairing, exposed areas and the environment matter. Isolation and drainage can be as important as the alloy choice.
Materials and Manufacturing Processes/Metals/Types of Steel
Addendum 74. Sources and quoted designation meanings
The Metals Service Center Institute identifies the first digit as “family of steel,” the second as “additional elements,” and the third and fourth as “nominal carbon content”; its example is 1018 at 0.18% carbon. Total Materia's SAE-AISI introduction gives the final two digits as “the carbon content in hundredths of a percent” and lists 41XX as “Chromium-molybdenum steels.”
The Aluminum Association's aluminum-alloy overview identifies these series and their principal additions. It describes 1xxx as “aluminum 99 percent or higher purity.” The series names do not list every element in an individual alloy; for example, the Association also identifies magnesium and possible copper and chromium additions in 7xxx alloys.
The Aluminum Association identifies 6061 use in truck and marine frames and 7075 use in aircraft. Metal Supermarkets' 6061/7075 comparison supports the T6 tensile-strength comparison, tank and tooling uses, machinability and welding differences. Its fabrication discussion notes that restoring the weld area's original temper in 6061 may require further heat treatment and aging. Compare the supplier's data for the actual temper and product form.
Addendum 77. Why an attractive surface can still be the wrong purchase
A shiny bar can have the wrong alloy, condition, straightness or size allowance. Conversely, inexpensive hot-rolled stock can be a sound choice when later machining removes the scale and establishes the final dimensions. Compare total processing cost, not appearance alone.
Addendum 78. Steel microstructures are not the four steel families
Ferrite and austenite are different iron-based crystal phases. Cementite is iron carbide, Fe₃C, a hard, brittle phase. Pearlite is a layered arrangement of ferrite and cementite. Martensite can form from austenite during sufficiently rapid cooling in suitable steel. These terms describe structure, not the buying categories carbon, alloy, stainless and tool steel.
Carbon can diffuse during slower transformations. Quenching can suppress those transformations and produce martensite. The outcome is not determined by cooling speed alone: chemistry and section size affect what forms throughout the part.
Addendum 79. Further reading on conditioning processes
Bodycote's heat-treatment overview provides entry points for annealing, hardening, tempering, stress relief and solution-and-age treatments. AEC's alloy and temper guide is a starting point for aluminum terminology. Neither an overview nor a qualitative sketch replaces a material-specific process specification.
Materials and Manufacturing Processes/Metals/Forming Metal
Addendum 81. Why a larger pattern does not replace a riser
Pattern allowance addresses final size. Feeding addresses a different problem: a solidifying region may need more liquid metal to avoid an internal shrinkage void. A riser must remain able to feed that region. The diagram identifies parts of a mold, not a production gating design.
Materials and Manufacturing Processes/Metals/Forming Metal
Addendum 82. Cold forming does not guarantee an unchanged dimension
Cold forming generally requires greater force than comparable hot forming. It avoids a separate hot-working step, but that does not prove every production cycle is faster. Springback, residual stress and later processing can change dimensions. Forging can also be hot, warm or cold; heat is not part of its definition.
Materials and Manufacturing Processes/Metals/Forming Metal
Addendum 85. Porosity can be useful or unwanted
Oil impregnation fills connected pores in a bearing so it can retain lubricant. Porite describes this use of porous sintered metal. That does not mean every powder-metal part is porous by design or that every part needs impregnation.
Materials and Manufacturing Processes/Metals/Joining Metal
Addendum 87. Why MIG is a familiar name but GMAW is the broader term
MIG refers to metal inert gas welding. GMAW also covers processes using active shielding gases or mixtures, often called MAG. Gas and filler selection depend on the alloy and process; the familiar shop name is not a complete welding specification.
A small active area coupled to a large noble area can suffer concentrated attack when both areas contact the electrolyte. That is why coating only the active member is not automatically a cure: a small defect in that coating can leave a small wetted anode coupled to a large cathode. The relevant areas are those participating in the wet corrosion cell, which can change as a joint dries. A compatibility decision must consider the complete joint and environment.
Addendum 93. How to check a center when a caliper touches the hole edge
Measure from the reference edge to the nearest hole edge, then add half the measured hole diameter to obtain that center coordinate. Use the same reference and direction as the drawing. This example does not specify a precision pin fit; a more demanding interface needs a more capable measurement method and a reviewed tolerancing scheme.
The nominal hole spacing is 70 mm, derived from 85 − 15. The separate ±0.5 mm x-coordinate limits can allow spacing from 69 to 71 mm. If an interface needs a tighter spacing, the designer must change the requirements; the inspector must not invent a tighter limit.
Materials and Manufacturing Processes/Manufacturing Documentation/Bills of Materials
Addendum 94. Consumption, purchase cost and batch yield answer different questions
You may need to buy a whole sheet even when one part uses a small fraction. That purchase is a cash requirement; the allocated fraction is the material estimate for the part. For a batch that consumes the entire stock unit, dividing its cost by the number of acceptable parts includes the loss from rejected pieces. Avoid charging the same waste once in the allocated share and again as an added allowance.
Addendum 95. Why there is no universal operation order
A feature may become inaccessible after assembly; a coating may need to be applied first. A larger blank may help holding, but its final cut must preserve the reference used for the holes. Record the reason for a departure from the usual sequence. The five process categories describe kinds of change, not a fixed order.
Addendum 96. Where to find product-specific instructions
Start with the manufacturer's product documentation, such as Smooth-On's technical bulletin and SDS directory. Its printed-pattern compatibility FAQ is a further-reading lead when investigating an uncured surface against a resin print. Check the complete instructions for the particular materials before selecting a treatment.
Addendum 97. Why a shorter cycle does not reduce every cost equally
A 10% reduction in a time-based processing charge reduces that portion by 10%. Material, setup and rent do not automatically fall. Capacity limits, tool replacement, scrap and quantity discounts can change the model outside its assumed range.
Equal variable costs mean the lower fixed cost wins, or both routes tie everywhere if fixed costs also match. A negative crossing lies outside positive production quantities. For a fractional crossing, compare costs at the neighboring whole-part quantities. This is process-cost break-even, not sales-revenue profit break-even.
Addendum 99. Why 20% loss means a 25% increase per useful amount
If 80% of purchased material reaches the product, one useful unit needs 1/0.80 = 1.25 purchased units, not 1.20. State whether a waste percentage is based on purchased material or on the useful amount.
Addendum 101. Why the loosest tolerance is not automatically cheapest
A tolerance that permits poor fit can increase assembly trouble, rework and failure. The goal is a manufacturable design that still meets requirements.
Addendum 102. Process time is not automatically value-added time
Rework takes processing time but corrects a failure. Inspection does not itself create the desired feature. A necessary machine cycle can transform the product even while the operator waits. Name whose time and which activity you are classifying.
Addendum 104. Bounded model reference: scheduling equations and limits
These equations describe the bounded ideal model; they do not report the current live settings.
For job i: A start = (i − 1)tA; A end = i × tA; transfer = min(ceil(i / batch) × batch, N) × tA. B start is the later of transfer and previous B finish; B end = B start + tB. Waiting before A = A start; held for batch = transfer − A end; waiting at B = B start − transfer. The three waits plus tA + tB equal that job’s completion time from order release 0.
Bounds: N 1–20 jobs, transfer 1–N, station times 1–20 whole min/job. This original scheduling example is separate from the map’s fixed 120-minute queue. It does not diagnose a factory or identify a universal optimal batch. Real setup, transport, limited space and variation can change the decision; no demand, quality or capacity forecast is made.
Addendum 105. A queue suggests a question, not a proven cause
A queue may reflect a capacity constraint, batching, missing information or an unreliable next step. Observe demand, timing and variation before calling one operation the bottleneck. A working day and a calendar day are not interchangeable time units.
