Precision Grinding

Controlled motion lets many small cuts produce fine size and finish

Precision grinding combines an abrasive wheel with controlled workholding and machine feeds. Each active grain removes a small amount. A dressed wheel, stable support, small finishing increments and temperature control can produce accurate dimensions and fine surface texture, including on hardened materials.

A smooth-looking surface is not proof of correct size or flatness. Wheel condition, vibration, heat and workholding can all affect the result. Inspect the drawing's requirements using Surface Texture and Finish and Tolerances and Fits. Choose the abrasive with Grinding Wheels and Abrasives.

Use Equipment Operating Procedure for operating preparation; see Machine Hazards and Housekeeping, Personal Protective Equipment and Metal Chips and Swarf for injury hazards and protective measures.

A surface grinder separates table travel, crossfeed and downfeed

On a horizontal-spindle reciprocating-table surface grinder, the table carries the work back and forth under the wheel. Crossfeed shifts the contact across the width of the work. Downfeed moves the wheel toward the work in small increments to remove thickness. Other surface grinders use different arrangements, including rotary tables.

After the finishing downfeed, sparking out continues passes without adding downfeed. The wheel can still remove a small amount as elastic deflection relaxes. Spark-out is not a substitute for measuring the part, and the number of passes is process-dependent.

A magnetic chuck holds suitable ferromagnetic work

A magnetic chuck uses magnetic attraction to hold suitable material such as many steels. It does not directly hold aluminum, brass or every stainless steel. Holding depends on material, contact area, thickness and the chuck's pole arrangement, not simply whether a magnet attracts one corner.

Clean mating surfaces and remove burrs that would lift the part. Use an approved fixture for parts that the chuck cannot hold adequately. A thin part can be pulled flat during grinding and spring back after release, so check the finished condition after removing the holding force.

Follow the chuck's release procedure after grinding. Residual magnetism may require demagnetizing so particles do not cling to the work. Demagnetizing is not the act that secures the work for grinding.

Count downfeed increments separately from table strokes

For an ideal plan with constant downfeed, number of increments = total thickness to remove / downfeed per increment. One increment may require many table strokes and crossfeed steps to cover the entire face. State what a “pass” means before using the equation.

Example: removing 0.024 in from one face at an assumed 0.002 in per full-face layer takes 12 downfeed increments. These are arithmetic teaching values, not machine settings. If the division is not exact, use a smaller final increment rather than removing extra stock.

Practice downfeed counts

Coolant helps control heat and carry away grinding debris

Grinding fluid can cool the work, lubricate contact and flush away removed particles. Heat changes dimensions during grinding and can alter the work surface. Delivery into the grinding zone, cleanliness and compatibility with the wheel and work material matter as much as having fluid in the tank.

Select the fluid and delivery method for the machine and operation. Do not assume every wheel or grinder permits wet operation. See Cutting Fluids and Application Methods for fluid selection and care, and Coolant Concentration and Mixing for mixing and measurement.

Cylindrical and centerless grinding control round surfaces differently

Cylindrical grinding commonly rotates work held between centers or in a chuck while a grinding wheel removes material from an outside diameter. Traverse grinding moves along the length; plunge grinding feeds into a selected width. Internal grinding finishes bores and can use rotating work or other machine arrangements.

Centerless grinding supports the work on a blade between the grinding wheel and a regulating wheel. The regulating wheel controls work rotation and, in through-feed operation, helps advance the work axially. The work does not need center holes. Infeed arrangements serve shapes that cannot pass straight through.

Each process needs its own setup and wheel selection. A fine finish alone does not establish roundness, straightness or size.