Critical Dimensions for the Shop
Choose dimensions from fit, function and interfaces, then give the maker and inspector the same references and limits.
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.
| Feature | Requirement | Reason / inspection |
|---|---|---|
| Material and outline | Birch plywood; length 100 ±1; width 40 ±1; thickness 6 ±0.5 mm. | 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.
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.