Abstract
Tolerance definitions and standards have been derived from manual inspection procedures. These interpret manufacturing errors through the use of comparative instruments, such as straight edges and height gauges. These tolerancing forms cannot be applied directly to inspection by coordinate measuring machines, where points on an object are sampled and assembled geometrically to allow features to be calculated.
In this paper an alternative approach is presented in which all tolerance conditions are recast into a series of allowable spherical deviations spread across the features to be measured. The distribution of these spherical zones and their radii are chosen, at the design stage, to provide checks on the various tolerance conditions required and to reflect the degree of confidence in the surface conditions provided by the manufacturing processes.
This approach has been employed within an automated inspection procedure to allow both top-down and bottom-up error checking procedures to be employed.