probe calibration problems

[varunner]

I could really use some help on this. My machine is a global fx, running pcdmis3.7mr3. The probe head is a PH10T usiug TP20 probe modules. During a probe cal I started getting standard deviation and stylus dia. errors of .01" - .02" on 2 particular angles. After trying the following: checking everything for tightness, cleanliness, deleating all .prb and .results files, rebuilding the tool file, reseting the "clearallwaikeys" file, changing stylus tips, changing modules we decided that the problem was a bad probe head. I consulted many different software support people at B&S and at one of their field offices. We installed a new probe head, and for a week there has been no problems. Now I'm having the same problems again. It's happening on several different angles now. Their have been no crashes either. Thanks in advance for any help.

Brian Carpenter

[JamesMannes]

That's a hard one to put a finger on. The only thing that pops into my head is check the squareness of the PH10T? It may have loosened and moved, not to say that would cause your problem, but it's worth a look?

[ag162]

What is different? temp? humidity? Is this cmm in a lab or on the floor? Do you print the results after all cals? If so, then you can look at the results and see the variations.

A.Gore

[Matthew D. Hoedeman]

Has your cal sphere been whacked? Is IT the problem? Is it loose on the stem? Don't just look at the head/probe, look at your tool too!

(sounds a little dirty, don't it? It's good advise anyway)

[varunner]

thanks for the responses. I made sure the head was square when the new one was installed, also had checked this on the old one. the cal shere is like new, tight and clean. the machine itself is a clean and temp controlled lab. The standard deviations are usually around .0000" - .0001". Now on several angles its .010" - .020"

[JamesMannes]

Not to be pushy, but, check it again for square and tightness? Just because it was square and tight when you installed it does not mean it still is squared and tight.

Again just a thought.

Also, are you using a PAA1, or "auto-knuckle" joint? The doo-dad that uses the little key to remove and replace a probe setup? Try a new/newer one sometimes those can give you trouble.

[ag162]

*Idea*
Have you tried calibrating without any extensions?

[ag162]

Also, check to make sure that the size of the spere is correct in the probe file.

[varunner]

the probe head was square and tight a week ago, but I'll check it again on Monday. I haven't been using any extensions, they're all short styluses, 20mm long, and no I do have the PAA1. I'm sure the size of the cal shere is good. when I calibrate, the probe file may have 10 different angles, 7-8 will be fine, 2 will be way out. Also I opened a program and calibrated the probe and all is fine. then opened a different program that uses the same probe file, and I have the the errors. I feel it's a software issue, because I've checked and replaced everything I can think of. I will double check all hardware issues once more on Monday

[JamesMannes]

It could be a problem with your scales(now don't quote me on this because I know virtually nothing about the actual mechanics of the machine(enough to be dangerous)), or the reader on the scales. Sounds like a BNS Calibration Tech should pay you visit. I may be jumping the gun, but thats' my thoughts and take them for what you will?
try moving the sphere to another location and, of course, say "yes" to the move question. It could be a dead spot on the machine?

[varunner]

If I can't get a handle on this by Monday afternoon, I'll set up a visit from a BNS tech.

thanks

[John Riggins]

You said the SD was off only on certain angles... makes me wonder about "flats" or other iirregularities in the Cal. sphere.

Just a thought.

[varunner]

Sometimes I wonder if there's something like that going on, but what's really bizzare, it that within the span of five minutes I can have a good cal in one program and a bad cal in another program. Both programs use the same probe file and the cal sphere is in the same location. When I get back on Monday, I'll clean and tighten everything I can get my hands on....again.

[TRD_racing]

varunner,
You may have already tried this but you said you had a Global machine. When you are calibrating have you watched it closely. The reason I ask is because my machine will take false hit. This may not be your problem, it sounds like you checked yours out pretty good but I am in the process of having all 3 of my axises fixed. The bearing and the belts on my machine are making noise at times. My measurement are good most of the time but sometimes it will take false hits just when it goes into the prehit distance. Check and make sure you are not getting false hit. When this happens your SD and your tip Ø will be off.

[varunner]

Dale,

what do you mean by taking a false hit? Completely missing the cal shere or taking a hit in an incorrect location? One problem that I had eariler was that when the probe was trying to take the first hit in the cal routine, it acted like it couldn't find the sphere.

Brian