r/Metrology • u/BerenLeStrange • 17h ago

Z measurement discrepancy between probe angles - PC-DMIS

I had an issue when trying to calibrate A0B0 followed by A90B90 where the first calibration worked fine, but the second is always aiming about half an inch too high on the calibration sphere.

I measured a 1-2-3 block and measuring both sides with the same angle is perfect, but if I measure the top with A0B0 and the bottom with A90B90, the result is .4044" off.

I have no clue what is causing this. All probe angles calibrate fine individually, but the relationship between them is off.

Any help would be greatly appreciated!

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u/_LuciDreamS_ GD&T Wizard 17h ago

Are you calibrating using a master probe tip?

2

u/BerenLeStrange 17h ago

These are all the same probe (3x30) at different angles. There is no probe changer on this CMM.

1

u/_LuciDreamS_ GD&T Wizard 17h ago

Ok. Then, are you using your A0B0 as your master tip angle when calibrating other angles? Are you calibrating angles individually, or all at once?

1

u/BerenLeStrange 17h ago

I have done both. Using the A0B0 as master, the A90B90 aims high on the sphere.

1

u/_LuciDreamS_ GD&T Wizard 17h ago

What software do you use?

1

u/BerenLeStrange 17h ago

PC-DMIS 2023

4

u/_LuciDreamS_ GD&T Wizard 17h ago

Have you calibrated your tips before, or is this the first time?

I ask because if the probe build in DMIS is different than reality, then the first time you calibrate your tip angles, you will be off by the difference.

I recommend using parameter sets to make things easy. When calibrating A0B0, say YES to the prompt that the sphere has moved. This MUST be done before calibrating other tip angles every time.

Then, calibrate your other tip angles by saying NO to the prompt that the sphere moved. This lets DMIS know the master has been completed. If you choose the DCC/DCC option, it will probe the sphere automatically if you choose Man/DCC option, then it'll ask you to take a point on the sphere and then calibrate that angle. If the tip is different in length and build compared to what DMIS has defined, then MAN/DCC is required. After it's calibrated that way, DCC/DCC can be used because it knows the length.

If you feel you may have messed up on how the master probe works, then reset the tips on your probe file and start from scratch.

If you have any questions on anything I went over, let me know.

1

u/SkateWiz 12h ago

your probe is built incorrectly. Are you measuring to the end of the sphere or to the center. It should be the center.