Measuring same circle at different rotations

[[Pe...]]

Hello, I have a curiosity about a measurement I was seeing.

I probed a circle in a ring gage using the same stylii, adjusting the A angle on the head each time. Looking at the X and Y values, I got some results that I'm not sure what to make of.

Setting X0 Y0 using the master probe, using a different probe to measure the same circle:

A 90° X-.0006 Y-.0001
A0° X.0000 Y.0001
A-90° X.0003 Y.0002
A180° X.0000 Y.0004

On each of these circles the diameter measured same as my ring gage and the roundness was .00007 at worst, and this was done with a freshly fully requalified probe.

Is this something to be concerned about? I would think a .0009 total difference in X and .0005 in Y seems a bit much.

[[Ri...]]

I brought this up in a post a while back for two CMM's with XTR Sensors.
Recently we had an RDS sensor added to one of the CMM's, the RDS carried the same issue with slightly less error.
These two CMM's are almost one years old.

[[Da...]]

What type of machine, what kind of sensor?

[[Pe...]]

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Using a Contura with XXT sensor

[[Da...]]

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Are you using the CAA correction for your probes? You could give the regular non CAA calibration a try. Use a high grade probe ball and clean everything very thoroughly. Use a very short stylus, too.

You basically have to eliminate every source of measuring uncertainty.

And also very important: Calibrate all the styli you need in one go.