Tolerance stack-up (1D)
One-dimensional tolerance stack-up with worst case and root sum square results. Add dimensions, set direction and tolerances, see whether the gap can go negative.
Tolerance stack-up (1D)
Chain the dimensions that set a gap, mark each one plus or minus, and see the worst case and statistical result. Catches the interference before the first article does.
| Dimension | Dir | Nominal | + tol | - tol | |
|---|---|---|---|---|---|
Nominal gap = Σ (sign · nominal)
Worst case = nominal ± Σ (tolerance in the hurting direction), every part at its limit.
RSS = √( Σ ((plus + minus)/2)² ) applied about the mean. Unequal tolerances shift the mean by Σ sign · (plus − minus)/2.
RSS is close to a 3σ band when each dimension is in statistical control and centered on nominal.
Worst case assumes every part is at its limit at once. RSS assumes each dimension is normally distributed and centered, which is fair for machined and molded parts in control, not for hand-adjusted ones. Use inches or millimeters, just stay consistent. Unequal tolerances shift the mean; the tool accounts for that.
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