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Calibration of styli

Before you begin taking measurements it is absolutely crucial that you calibrate the probe precisely for all your measurement procedures.

The effective dimensions of the probe components have to be established if good results are to be obtained. These values are stored in the machine's data processor.

In the case of CMMs, this may involve calibrating several styli or sensors, often in multiple head orientations. Calibration of machine tool inspection probes is generally simpler.

How it works

The position of the individual ball styli and their diameters are established using a special probe calibration programme (see the machine manufacturer's user manual).

You contact a reference point with all the styli used, one after the other. The reference used is usually an extremely precise, manufactured ball with a known diameter (referred to as a datum ball). The exact dimensions of the ball being calibrated are input to the measuring software.

If the styli are to be used for measuring separate points, the stylus is calibrated using 5-6 points on the reference ball's high points.

A far greater number of points are probed in scanning systems. The machine manufacturer's user manual will describe the precise probing strategies for calibrating the styli.

Make sure, particularly if you are using more than one CMM, that you use the calibrated datum ball whose values have been input to the software.