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Getting the most out of your measuring process.
When you talk to Eugene Gleason, president of the Baltec Div of Micro Surface Engineering, Los Angeles, CA, you get the feeling that he is on a mission to eradicate error from coordinate measuring machines wherever it occursbefore the fact. As he explains it, errors can result from any number of causes. The two most prominent ways of eliminating these causes: 1) Calibrate machines properly, even daily, using a ballbar; 2) Use fixtures that meet the specific needs of CMMs.
"You know there are eight orthogonal positions and 21 possible errors in a CMM, 18 of which can be readily checked," Mr Gleason says. The secret, he believes, is to check the CMM for accuracy, almost on a daily basis with one of the most economical of artifacts, the ballbar.
A ballbar consists of two very round spheres of exactly the same size firmly attached to opposite ends of a rather long, rigid bar at a fixed and known distance. The ballbar is located on a robust vertical stand that can be located in various positions throughout the volume of the CMM that is being checked.
The accuracy of the ballbar, however, does have a single, yet major, limitation, according to Mr Gleason. "A conventional free-standing ballbar will bend when the contact force of the measuring probe is applied to it. The longer the ballbar,...