Automotive Steel Partners

If you do any work with steel stampings then you may find the work of the Automotive Steel Partners useful. One publication that they have gives some guidelines for establishing and evaluating CMM measurement:

Automotive Body Measurement System Capability Gage Capability for CMM Data Evaluating the capability of a CMM differs slightly from a check fixture. Since CMM measurements are taken using automatic programs, manufacturers generally are not concerned with the operator or reproducibility effect. In this instance, the gage variability for a CMM consists primarily of repeatability. Some manufacturers, however, break CMM gage repeatability down to static repeatability and dynamic repeatability. Dynamic repeatability, or setup error, represents the ability to measure identical part characteristics using the same gage on the same part with loading and unloading between measurement trials. In the case of static repeatability, the part is not unloaded or unclamped between trials. Thus, static repeatability represents the pure error in the measurement instrument. These data suggest that the dynamic repeatability, based on the setup or loading/unloading of the part in the holding fixture, is the main source of CMM gage error. Here, more than 90% of the repeatability error repeat may be attributed to loading and unloading of the part between measurement trials.