Manufacturing operations throughout the industry have ignored geometric bonus tolerances, caused by varying feature sizes, when assessing statistical process capability from variables data. Attribute gages, or hard gages, address the bonus tolerance physically but do not produce the variables data that is needed for statistical reporting. The problem thus far has been integrating the variable feature size with the geometric form, location or orientation deviation in a simple, effective method and reporting the process capability. A solution to this problem may be at hand.
Process capability assessments derived from variables data gaging devices --
electronic gages and coordinate measuring machines -- can be computed from the residual or remaining tolerance of a feature rather than the consumed tolerance. The residual tolerance (Rt) is equal to the sum of specified location or orientation tolerance plus the individual feature bonus tolerance less the individual measured form, location or orientation deviation.