Frequently Asked Question
Assembly closure
Tolerance stack-up should model the functional closure of an assembly, including datum scheme, direction, sensitivity, and distribution. Worst-case analysis guarantees the limit; statistical analysis requires credible distributions, centering, and process control.
ai is the sensitivity coefficient and Ti is an individual tolerance.
Worked example
For three one-to-one contributors of ±0.10, ±0.06, and ±0.04 mm, worst-case variation is 0.20 mm and RSS variation is √(0.10²+0.06²+0.04²) = 0.123 mm. Select the method based on the assembly risk and process evidence.
Engineering check
For Tolerance Stack-Up for Assembly Interfaces, maintain traceability from requirement to risk, design output, evidence, and approval. Record the configuration, acceptance criterion, test or analysis conditions, open actions, and residual risk. A method is not complete when the document is filled in; it is complete when the evidence supports the decision and affected controls are updated.
Engineering note
For Tolerance Stack-Up for Assembly Interfaces, state the intended use, input range, dominant mechanism, units, boundary conditions, acceptance criterion, and evidence owner. Use an independent balance, limiting case, repeat measurement, or sensitivity check to challenge the result. Document the configuration and uncertainty so another engineer can reproduce the reasoning and determine whether the result remains valid after a design, material, boundary, or process change.
Engineering note
For Tolerance Stack-Up for Assembly Interfaces, state the intended use, input range, dominant mechanism, units, boundary conditions, acceptance criterion, and evidence owner. Use an independent balance, limiting case, repeat measurement, or sensitivity check to challenge the result. Document the configuration and uncertainty so another engineer can reproduce the reasoning and determine whether the result remains valid after a design, material, boundary, or process change.