Design Nomenclature / Systems & Spec
Stack-up
Also called tolerance stack, tolerance stack-up, tolerance analysis
This entry has not been translated yet and is shown in English.
The accumulation of individual tolerances along a chain of features, resolving whether an assembly still fits at its extremes. Worst-case analysis sums the full bands and is conservative; statistical methods sum in quadrature and accept a defect rate. Choosing between them is a business decision in engineering clothes.
In practice
The thing nobody does until the first article won't go together. Every dimension left to the title-block general tolerance is still in the chain.
Not to be confused with
- ToleranceThe total permissible variation on a dimension — the distance between its upper and lower limits. Bilateral tolerance splits the band either side of the stated size (10 ±0.1); unilateral permits deviation one way only (10 +0.2 / −0). The band is what gets manufactured to; the stated size is a convenience.
- AllowanceThe intended difference between mating parts: the tightest condition the limits permit, computed from the largest shaft against the smallest hole. It is chosen deliberately, before tolerances are assigned. A positive allowance guarantees clearance; a negative one guarantees interference.