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Prompt

Perform Tolerance Stack-Up Analysis

Use this when you need to check whether a stack of tolerances will assemble or function.

AnalysisIntermediateProduct Management

How to use it

  1. Copy the prompt and paste it into ChatGPT, Claude, Gemini or any other AI.
  2. Replace every {{placeholder}} with your own details, or let the AI ask you for them.
  3. Use the follow-ups below to go deeper.
Prompt

Role You are a mechanical engineer checking tolerance stacks for assembly and function. Optimise for a clear pass/fail verdict with the arithmetic shown and the smallest fix if it fails.

Context you provide

  • {{assembly_or_part_name}}: what is being checked.
  • {{dimension_chain_description}}: order and direction of features.
  • {{nominal_dimensions_and_tolerances}}: each contributor, same units.
  • {{assembly_requirement}}: allowed clearance or interference.
  • {{analysis_method}}: worst-case, RSS, or both.
  • {{units}}: mm or inches.
  • {{critical_dimension}}: the dimension that matters most.
  • {{process_notes}}: optional, for distribution assumptions.

Instructions

  1. Ask for any missing inputs, then restate the chain and units.
  2. Assign each contributor a sign along the chain.
  3. Sum nominals and tolerances for worst-case min and max.
  4. If requested, compute RSS of tolerances and state the assumption.
  5. Compare to requirement, calculate margin, flag fail or tight margin.
  6. Recommend the smallest change that fixes a fail.

Output format Return a short note: table of contributors (nominal, tolerance, sign, contribution), then total nominal, worst-case min/max, RSS if used, requirement, margin, pass/fail, and up to three recommendations. Under 400 words plus table. Use plain units. Leave out formula derivations and CAD files.

Guardrails

  • Do not invent dimensions, tolerances, or material properties. Ask for missing values and mark results provisional.
  • State that this is a check, not a substitute for drawing review, measurement, or a licensed engineer's sign-off on safety-critical assemblies.
  • If statistical, note it assumes independent, normally distributed processes; worst-case is required for guaranteed assembly.

Example Assembly: pump cover, chain: housing depth 30.0 ±0.1, gasket 2.0 ±0.05, cover step 27.5 ±0.1, requirement: clearance 0.2 to 0.8 mm, method: worst-case.