SuperNX / Tools / Stack-up calculator
Tolerance Stack-Up Calculator
| Part / feature | Nominal (mm) | ± Tol (mm) | Dir. | |
|---|---|---|---|---|
| Method | Closing gap (nominal ± var) | Min | Max |
|---|---|---|---|
| Nominal | 0.100 mm | — | — |
| Worst case (ΣT) | ±0.200 | −0.100 | +0.300 |
| RSS (≈±3σ) | ±0.122 | −0.022 | +0.222 |
worst caseWorst case goes negative (−0.100 mm) — the chain can close up (interference / no gap). RSS says it is unlikely, but not impossible.
How to read the two answers
- Worst case (ΣT) assumes every contributor sits at its worst extreme simultaneously — a 100% guarantee, paid for in tight tolerances. If the worst-case band stays positive, nothing can ever interfere.
- RSS (root-sum-square, ≈±3σ) treats the contributions as independent variation — realistic for stable processes, but it is a yield estimate, not a guarantee. A negative RSS tail means a small scrap/rework rate, not certain failure.
Direction matters: a feature whose growth increases the gap gets +, one that eats into it gets −. The worked default is a classic axial chain — housing depth minus two stacked internals.
Deeper dive on when each method is honest: worst-case vs statistical tolerance analysis and the stack-up guide. General-tolerance defaults for undimensioned ± values: /data/iso-2768.json (ISO 2768-1, class m is the common default).