Choose functional datums
For a mating tail, locate support relative to the contact pattern and insertion edge. For a mounted component, locate it relative to the support footprint and mounting features. Avoid long dimension chains from unrelated outline edges. The tolerance planning guide helps identify which dimensions should be independent functional requirements.
Separate tolerances by function
| Feature | Define | Review |
|---|---|---|
| Thickness | Completed reinforced section | Mating or enclosure fit |
| Position | Support relative to functional datums | Coverage and free-span boundary |
| Adhesive extent | Bond area and contact keepout | Clean exposed features |
| Outline | Support edges and cutouts | Assembly clearance |
Separate material and position limits
Specify support thickness separately from in-plane position, adhesive coverage, and edge clearance. A support may be correctly aligned while adhesive reaches a prohibited area. Use attachment-method planning to connect the drawing limits to positioning and bonding controls. Ask the proposed fabricator to review the combined functional requirement rather than only individual nominal dimensions.
Make the inspection unambiguous
Show the inspection face and identify whether limits apply before or after assembly. Define how a hidden support edge or bondline will be checked if it controls fit. For a connector, compare the completed tail envelope with the selected drawing at the relevant limiting conditions. Resolve conflicting artwork, mechanical drawings, and three-dimensional models before release; they should describe the same datum scheme and acceptable region.
Before you release the design
- Use functional datums.
- State the inspection face and stage.
- Show adhesive limits separately.
- Review accumulated variation at the interface.
- Resolve conflicting dimensions across deliverables.
Watch points
- Assigning tight tolerances everywhere can obscure the few dimensions that actually control fit.
Practical questions
Should the same tolerance apply to support and adhesive edges?
Not automatically. They serve different functions and may need different limits and inspection methods.
Can a nominal CAD overlap prove contact clearance?
No. Review the completed interface with agreed variations in position, outline, and adhesive extent.
Technical references
References support the material or design context. Check the exact grade, part number, document revision and project conditions before release.Updated 27 September 2026 · Technical content policy · Engineering guidance supports project review; the agreed drawing defines the build.