Statistical Capability Analysis for Geometric Tolerances Using the MMC Modifier

Several geometric tolerances are permitted to have the Maximum Material Condition (MMC) modifier after the tolerance value in the Feature Control Frame. This modifier has the effect of increasing the geometric tolerance available for each feature based on the actual size of that feature. The geometric tolerance provided by the specification is, therefore, variable. To verify that one part is within the geometric tolerance is quite straightforward. To assess the statistical capability of an entire population with respect to an ever-changing tolerance, however, requires a redefinition of the specification and a modified approach to calculating and interpreting the statistical capability.