Mark,

The first thing I always do, prior to a calibration, is qualify the touch probe on the sphere. Look at the diameter and sphericity info after qualifying your probe. TP20's and 200's when whacked hard enough will not qualify. They will give you various different symptoms, but mainly you will see the diameter and sphericity of the requal sphere to be way off. A number of other factors will also come into play. Length of stylus, diameter of probe, etc... Keep a "golden" TP200 handy for comparison. You never know what the guy on third shift did or did not do to your CMM last night.

Mark Lidstrom
Field Service Engineer
Quality Vision Services Inc.