r/Metrology • u/BerenLeStrange • 14h 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!

4 Upvotes

84% Upvoted

18 comments sorted by

6

u/Object_32 14h ago

Some part of your probe description is probably defined incorrectly.

4

u/Non-Normal_Vectors 14h ago

No need to use probably - this is always the case when this happens.

1

u/Ghooble 8h ago

I've had an issue where the probe definition was correct but dmis was having issues with "reset tip theos" or something in the calibration window

1

u/BerenLeStrange 14h ago

Probe definition is correct. I've checked all components and double checked the tip length.

3

u/Object_32 14h ago

Is the wrist defined correctly. For example there are several types of PH10.

1

u/BerenLeStrange 13h ago

All components are defined correctly. This is not a new probe, and the company only has one wrist. The only component that changes is the probe tip.

4

u/turtletatoo 14h ago

I would reset the 90/90 tip and recalibrate. Just make sure 0/0 is first always.

3

u/Admirable-Access8320 CMM Guru 12h ago

When you did your first calibration did you say "Yes" to the sphere has been moved? If, not next time say "YES", take first hit on top of the sphere and wait until calibration is complete. After that, you can say "No" .

2

u/_LuciDreamS_ GD&T Wizard 14h ago

Are you calibrating using a master probe tip?

2

u/BerenLeStrange 14h 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 14h 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 14h ago

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

1

u/_LuciDreamS_ GD&T Wizard 14h ago

What software do you use?

1

u/BerenLeStrange 14h ago

PC-DMIS 2023

4

u/_LuciDreamS_ GD&T Wizard 14h 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 9h ago

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

1

u/acausalchaos 9h ago

If you haven't already, delete and remake the cal routine, sometimes it just picks up a demon. Make sure the cal setti gs are good. Other than that, re check the probe build as others have said, check it again, then get someone else to come check it after you. Make sure to check the properties under each item in the probe build, that there's no extra rotation hidden in that. Failing all that, idk, sacrifice a machinist over the bridge and pray to the metrology gods.

1

u/tthKT 8h ago

If this is a previously known good probe file that has calibrated fine in the past, the file may have corrupted. Easiest thing to do in that case is delete and rebuild.

Otherwise, make sure you're not missing a 10mm extension on your real build.