Tolerancing of component dimensions in CAD

Any particular dimension of a manufactured component varies in its value between individual nominally identical components. When several components are to be assembled together, it can happen that in some cases assembly will prove impossible, or that the assembly may not satisfy design specifications. The problem arises to optimize dimensional tolerances to ensure that, for given manufacturing costs, there is an acceptably low risk of the assembly failing to meet the specification. Approaches for solving this problem are discussed. The ability to associate a chosen set of nominal dimensions and dimensional tolerances with a numerical estimate of the risk of unsatisfactory assembly is found to be of considerable value in computer-aided design procedures, where it is necessary to optimize tolerances for minimum overall cost.