Probe results

[gage guru]

When you calibrate a probe tip you get the results which shows the X, Y, and Z as well as the diameter and the sntd dev.

What does the x,y,z represent and if it is off how does that affect anything.

I realize that when you get into head rotations that you need to relate to 0,0 and the other angle as if you don't you will be off(I am talking from a recent experience here).

That is why hence the question, because once it was calibrated properly the Z value changed and the points taken were "more correct".

But just for a 0,0 the value we have as nominal is 180 and the results are 178 something....

On the other CMM same setup the nominal is again 180 and the results are more @ 180ish.

Sorry do not have specifics, but the idea is that the results are off.

My initial thoughts are this:

the values represent the distance from the center of the ruby to the bottom of the ram where the pH head goes into.

If anything is off it is relative to perhaps the head is not seated all the way up as it should(i.e. someone messed around).

OK I am done babbling my questions thoughts and own answers - I await your expert answers to help me.

P.S. Is it time for a beer yet??? I figured I would include beer right away because it is the 3rd monday of the week and I am well overdue to have one about now!!!


Thanks!!!!!!!!!!!!!!!!!!!!!!!

[Matthew D. Hoedeman]

The results will show you the deviation from perfect. Since the extensions, probes, cartridges, etc. will all vary in both length and perfect straightness, you will get different values for each.

I have long been a beliver that ALL angles should be calibrated at one go and since your PH9 (whatever) when it indexes SHOULD position the probe on the surface of a sphere AT EVERY ANGLE, then you should calibrate a minimum of 4 angles (4 points minimum to make a sphere) in a probe file to get the most accurate results possible. For example, if you only calibrate a single tip at 0,0 on a new ball location, your results for it will be perfect, when we KNOW that is impossible. However, if you calibrate 4 or more, then the actual error of your hardware and buildup will show up in the calibration.

[jmgreen]

I went thru a similar problem when I first started using PCDMIS and qualifying probes. The X, Y, and Z values are the location of the Ruby center in reference to the machine 0, 0, 0 cordinates or rather the referenced center on the arm. So you are correct in your assumptions. In my case we have a Horizontal machine and it took a while for tech support to figure out the correct orientation of the probe head. You could be right in that the head is either loose or skewed some how. A couple of things to check:

• Check your probe orientation (edit->preferences->setup->Part/machine->Probe Head Orientation) to make sure it is set properly.
• Check your probe build (insert-->Hardware definition-->Probe) to make sure you built the probe correctly. You may also need to rotate it to get it correct.
• Also check your head (heh heh, he said head) to make sure it is properly seated. I ended up taking rough measurements with a scale from the center point to the ruby in order to convince tech support it was not correct. Took a while for us/them to understand my situation.
• Another trick I've learned is to set up a pointed piece (I use the pointed/scribe probe from the probe set) on the table and get as close to the tip as possible with your probe, then rotate it and see if it remains in the same place in reference to the point. try it at A0B0, A0B180, A0B-180 and then A90B+180 and A90B-180.

Hope this helps, sorry for the length.

[gage guru]

Understood. For the most part as this was discussed further today we are mostly trying to define from one CMM to the other the difference in the Z height in the results after calibrating a 2 X 40 tip and should they be pretty close. CMM in question has a result z of 178.367. The other CMM has 180.001??

More discussion is going on this end......anyone have some more expert advise?? Thanks

[bob mappes]

are you using the same calibration ball on both cmms?

or are they two different ones with two different heights?

on the non-expert side.....what does it really matter? they are two different machines....they have assembly tolerances.....as long as they both are able to verify that parts being inspected are good......who cares?

have you tried checking one part on both machines and compare those results? that is where it will matter most

just my $0.02

[JamesMannes]

Another FYI...
If these CMM's are on the net, do not use the same probe files for both machines. You are destoying the Qualification from the one when you do the other CMM. I'm not assuming that you are doing this, I'm just stating something that has come up on this board before.

[gage guru]

Bob - James thanks for the feedback. I understand what you say and the last discussion was to have the person who runs them measure a part on one and then the other. I am just trying to get a better understanding of what the probe results tell us so that we can use it as a tool to when a calibration is not correct. This happened just last week and caused 2-4 days of delay and my boss is wanting to get more info so we can avoid and have the person running them more aware of what is going on!!!

Very frustrating.....could have been all avoided if just done right the first time. ON top of that it takes away from the credibility of the lab.