A statistical approach to tolerance evaluation for circles and cylinders

Sample data points obtained from a Coordinate Measuring Machine or other similar inspection system are frequently used to evaluate part conformance to specification. Typically, a curve or surface is fit to the sampled points and the decision is based on parameters of that curve or surface. This paper presents an approach to tolerance evaluation that explicitly considers underlying part variation under the assumption of normality of errors. Statistical inferences on the parameters are used to evaluate size and position tolerances. Results are presented for a simulated feature with normally distributed errors and for a measured feature.