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Tolerance stack-up

Worst-case vs statistical.

Tolerancing

Overview

Tolerance stack-up analysis adds up the individual part tolerances across an assembly to verify the whole thing still fits and works. It's how you catch interference or gaps before manufacturing.

How it works

Tolerancing
ChainSumStatOutputDimsstackWorst-caseΣ±RSS√Σt²Fit check
ClientServiceEdgeData

Step by step, with examples

  1. 1

    Dims

    • List every contributing dimension.
  2. 2

    Worst-case

    • Add tolerances linearly.
  3. 3

    RSS

    • Root-sum-square for a realistic spread.
  4. 4

    Fit check

    • Confirm the assembly fits.
    • Example: gap ≥ 0

Overview

Sum tolerances along an assembly path; worst-case guarantees fit, RSS (statistical) is realistic for volume production.

Common pitfalls

  • Mixing worst-case and RSS
  • Ignoring thermal expansion
  • Forgetting fastener clearance

Where this content comes from

For full transparency, this content is curated and verified from these sources:

ASME Y14.5 GD&T standardParametric CAD vendor documentationOppZen-authored CAD design guides