Engineering Reference

Virtual condition

The worst-case boundary of a feature, combining its size and geometric tolerance.

Definition

Virtual condition is the envelope that the mating part must clear. For an external feature it is MMC plus the geometric tolerance; for an internal feature it is MMC minus the tolerance.

It is the number that determines whether an assembly will go together — not the size limit and not the positional tolerance, but the two combined. Tolerance analysis on clearance fits should be done against virtual condition.

Common misuse

Checking positional tolerance at MMC without computing virtual condition. The assembly may still interfere even though each tolerance passes.

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