Machine Design #97: Allocate Tolerance by Function — Tight Where It Matters, Open Where It Can
MINATA turns the Vietnamese source into an evidence-led guide. functional tolerance allocation must preserve function, manufacturability, inspectability, cost, and serviceability when the boundary changes.
Function before a number
Write the input, expected result, acceptance limit, failure symptom, and measurement method before choosing a thickness, tolerance, datum, or hole pattern. Assign an owner to every value and change.
Core checks
- Functional characteristic and acceptance limit: record value, source, method, owner, and pass/fail evidence.
- Stack contributors and datum scheme: record value, source, method, owner, and pass/fail evidence.
- Process capability and supplier risk: record value, source, method, owner, and pass/fail evidence.
- Worst-case versus statistical allocation: record value, source, method, owner, and pass/fail evidence.
- Inspection effort and measurement uncertainty: record value, source, method, owner, and pass/fail evidence.
- Cost, change, and reallocation rule: record value, source, method, owner, and pass/fail evidence.
| Failure mode | Symptom | Verification |
|---|
| Function not defined | Over-tight or weak design | Rebuild the functional stack |
| Datum not real | Inspection and assembly disagree | Try the real fixture |
| Documents out of sync | Correct number, wrong revision | Baseline every reference |
1. Review pass: function and load path
Review function and load path for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
2. Review pass: datums and interfaces
Review datums and interfaces for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
3. Review pass: process capability
Review process capability for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
4. Review pass: assembly and maintenance
Review assembly and maintenance for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
5. Review pass: inspection and uncertainty
Review inspection and uncertainty for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
6. Review pass: failure and recovery
Review failure and recovery for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
7. Review pass: supplier and acceptance
Review supplier and acceptance for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
8. Review pass: revision and change
Review revision and change for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
9. Review pass: cost and trade-off
Review cost and trade-off for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
10. Review pass: safety and misuse
Review safety and misuse for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
11. Review pass: data and audit
Review data and audit for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
12. Review pass: training
Review training for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
13. Review pass: field feedback
Review field feedback for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
14. Review pass: release evidence
Review release evidence for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
15. Review pass: function and load path
Review function and load path for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
16. Review pass: datums and interfaces
Review datums and interfaces for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
17. Review pass: process capability
Review process capability for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
18. Review pass: assembly and maintenance
Review assembly and maintenance for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
19. Review pass: inspection and uncertainty
Review inspection and uncertainty for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
20. Review pass: failure and recovery
Review failure and recovery for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
21. Review pass: supplier and acceptance
Review supplier and acceptance for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
22. Review pass: revision and change
Review revision and change for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
23. Review pass: cost and trade-off
Review cost and trade-off for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
24. Review pass: safety and misuse
Review safety and misuse for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
25. Review pass: data and audit
Review data and audit for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
26. Review pass: training
Review training for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
27. Review pass: field feedback
Review field feedback for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
28. Review pass: release evidence
Review release evidence for the functional tolerance allocation. The key risk is functional stack, capability, cost, inspection, and balanced interfaces. Define lower and upper boundaries, the simultaneous worst case, evidence source, owner, and change trigger. Confirm model, drawing, BOM, material, process, inspection, and work instruction use the same revision. Test normal assembly, variation, wrong input, interruption, and a controlled fault. Record actual value, unit, condition, instrument or log, sample or serial, pass/fail, and next action.
MINATA release checklist
- [ ] Function, boundary, and failure symptom are written.
- [ ] Datums, ownership, process, and mistake-proofing are clear.
- [ ] Six topic checks have evidence and pass/fail limits.
- [ ] Manufacturing, assembly, inspection, and maintenance were tried.
- [ ] Revision, supplier, material, and configuration records agree.
Good engineering is an explicit chain that survives manufacture, operation, maintenance, and change. For functional tolerance allocation, evidence that function and variation remain reliable is the MINATA standard.
Public references
- MINATA Q-up design practice and internal review checklist.
- Applicable drawing, material, molding, or quality standard selected by the project owner.
View all MINATA technical articles