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Tip Calibration

Posted: Thu Jan 16, 2020 7:06 pm
by FialekJared2018
Currently having some issues when calibrating tips, we have two probe assemblies for various parts. When calibrating the tips we get outcomes bigger then what the ball size is...for instance A0B0 comes out with a result of 2.019. This happens to all tips for 2mm ball and then for our 3mm ball we get big outcomes as well? Probe assembly build is correct in length for both. I have included a photo as well.
tips.JPG
If anyone can give me some ideas or what is causing this, it would be very helpful! Thank you.

Re: Tip Calibration

Posted: Thu Jan 16, 2020 8:56 pm
by Acuity_Metrology
This is usually caused by a loose stylus, but if your form error is good and you are getting similar oversize on two different assemblies, it isn't likely the issue in this case.

When you measure the sphere, do you get the expected diametrical and form results?

Re: Tip Calibration

Posted: Fri Jan 17, 2020 10:00 am
by CMM Guru
Jared,

Can you give a bit more detail of your actual probe build? PH10? PH20? TP20? Std force module? Stylus length? Extensions used?

Being oversize (at all positions) is indeed odd, and would typically be from something like a loose stylus. But you say you have two assemblies doing it which is really odd.

In the end, Acuity is correct. If it measures a standard correctly the calibration is good (usable). Although I would indeed be looking for causes!

Re: Tip Calibration

Posted: Fri Jan 17, 2020 11:07 am
by Ryan Christopher
As you are investigating this, it wouldn't hurt to check your definitions too...

1. Make sure that in the Probe Assy dialog box, the stylus is defined in mm as being the nominal 2mm.
2. Find the Calibration sphere definition and make sure that it is defined as being the actual calibrated size.
RIBBON > PROBE > SETUP group >SETUP CAL. SPHERE

Re: Tip Calibration

Posted: Fri Jan 17, 2020 3:31 pm
by FialekJared2018
We have a PH10 to a TP20 using standard force module with an extension of 10mm to a 2mm ball stylus which gives overall length at 177 for Probe assembly 0....for the second one its all the same but no extension and is a 3mm ball stylus with overall length of 167.

Re: Tip Calibration

Posted: Tue Jan 21, 2020 9:53 am
by CMM Guru
The "build" lengths seem correct. And since you have two probes (two different modules) it would seem unlikely that both would be loose, and by the same amount!

I'm assuming this is a machine that has been running for some time? If so, were there any recent changes? It is possible that speeds and/or accelerations are not optimal (ie: running into the touch point way too fast!) giving bad results.

There are two things I'd like you to try.

1) After calibrating your probes, measure a "standard" such as a known ring gauge. If you do not have that, re-measure the sphere. In either case, the actual should be exceptionally close to the nominal. ie: a 25.4 mm cal sphere should measure as 25.4 within a micron or so.

2) if you have access to a *known* length bar - ie: 500mm, could you check the length? Inspect a plan on one end, then a point on the other, and ask for distance point to plane. If it is a certified or known 500mm, once again, your value should be within a micron or so (depending on temperature). This will make sure your scale factor is correct.

Although it is not unusual to have 1 or 2 "angles" calibrate slightly over nominal, to have them all over nominal, and that far over nominal is exceptionally unusual. This is indeed indicative of something not quite right in the system.