runout/concentricity issues with 1 CMM but not the others.

[[RP...]]

Recently we've had issues with one of our three Duramax CMMs reporting runout or concentricity 0.002 higher than the other two CMMs or concentricity gages.  All the CMMs share the same programs, calypso 2021, and same probes.  Measuring the sizes seems to be no issue.

CAD Presentation outputs the same visual, on either side of the cylinder.  Even after flipping the part.

What could be the main causes?

I've tried switching the fixtures.  rotating the part.  recleaning probes and the part.  each machine is qualified only once a week.  Any suggestions appreciated.

I have a step cyl from recalling circles 1 and 2 for spacial, nothing in planar, x and z origins are step cyl.  back plane is y origin.

[[Da...]]

Main cause that comes to mind is skewed scales due to a crash. Even seemingly harmless crashes can cause a machine to go out of spec. When was the last time the machine was serviced?

[[RP...]]

We had a technician calibrate the machine last month.

[[RP...]]

It was aluminum build up.  Replacing the probes seemed to have fixed the issue.

[[Jo...]]

Just thinking out loud:

How can it be buildup, when you use the same probes and the same program on all machines?

Or did you mean similar probes?

[[RP...]]

Same program, similar probes.  I'm just assuming that's what it was since the reports are now green and that's all the operators care about or understand.

But that machine constantly checks aluminum parts that aren't checked on other machines because of the fixturing and space needed.

I measured the probe on a keyence unit for the heck of it.  The ruby seems to be .002 off the center of the shaft?  Maybe it did crash and nudged the probe out of place? I didn't think the position of the ruby mattered.  The dark green lines are from the high and low points of the ruby while rotating in 30 degree increments.  The longer dark green line is the average of the 12 lines.  Looks like theres a pattern, but I can't figure out if it's significant to anything.

 

[[Ri...]]

A probe qualification should have taken care of this. If you are measuring aluminum, I would advise strongly against using ruby. 

[[RP...]]

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I agree.  If we had more space on the duramaxs, I'd put a nitrade stylus system on them for the aluminum parts.  I've told our higher ups about that too.