Identify functional dimensions
Separate mating thickness, insertion geometry, locating holes, component alignment, and enclosure clearance from dimensions that merely describe shape. Start with the actual connector-tail drawing when a terminal controls the interface. Record the reason for each tight requirement so a manufacturing discussion can evaluate alternatives without losing the product’s functional intent.
Functional tolerance review
| Requirement | Question to resolve | Drawing or process record |
|---|---|---|
| Mating thickness | Which local layers contribute? | Section view and finished requirement |
| Tail alignment | Which edge or feature locates the contact pattern? | Datum and positional definition |
| Branch location | Is the measurement free or restrained? | Fixture or restraint instruction |
| Stacked parts | Which variations combine at the interface? | Tolerance-chain review |
Choose datums and restraint conditions
Explain how a flexible part is located during inspection and whether it is free, flattened, or supported in a fixture. Align those references with the product where practical. Use the fabrication drawing to show local section tolerances separately from overall dimensions. Avoid asking a floating branch to satisfy a rigid-body measurement without defining its restraint.
Review the tolerance chain
Include adhesive, finish, reinforcement position, cut edges, and mating-part variation where they affect fit. Discuss which contributors can be controlled and what inspection is meaningful. Keep proposed supplier allowances separate from approved drawing requirements. If the design depends on a dimension the supplier cannot verify as written, revise the measurement plan before accepting a nominal sample.
Before you release the design
- Identify the functional purpose of every unusually tight dimension.
- Use the same datum interpretation across CAD and inspection.
- Specify finished values where the interface needs finished values.
- Agree how ambiguous or out-of-tolerance results are handled.
Watch points
- Do not substitute a nominal layer sum for a finished thickness tolerance.
Practical questions
Should I apply the tightest tolerance to the whole drawing?
No. Assign tolerances to the functional requirements and agree manufacturability. Blanket tight limits can add inspection and cost while leaving the important local interface poorly defined.
Why did two inspectors get different outline measurements?
Check restraint, datums, temperature or conditioning where relevant, and measurement technique. A flexible shape may not have a unique free-state position.
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.