Different results with different probe rotations.

[[Pe...]]

Hello I am seeing some odd results within our rotations and was wondering if anyone could offer some insight:

This is on a contura with rds xxt.  My stylus is a 1mm probe X 30 long, on a 60mm long extension, qualified as RC-CAA.

I establish a Z zero at A0 B0.

Then I check the same Z at different rotations and get some different values:

The + or - are the Z results.

This is with a fresh new stylus, with a full qualification.

I tried it with a different stylus, a longer one, and got even worse results (±.0007).  I tried the same test on a different cmm and got ±.0001.

I don't know what to do with this or if there is anything I even can do.

[[Ri...]]

Create a List of the same rotations and re-test.

Post the results.

[[Wo...]]

Our RDS has suffered a few substantial crashes and during rotation it would "click" and visibly jerk a little. It would be OK right after qualification and then a day or two later it would start showing major differences. Fortunately we've also had the XT head so we just stopped using the RDS. Maybe there is some physical damage? Would be a good test to be able to use another probehead on the same machine and see if it fixes the problem. 

[[Ri...]]

Since this is with RC-CAA qualification, this is expected. The longer the stylus system the worse error will be for the qualification. 

It has always been stated that if you need accuracy, do not use RC-CAA, instead create the individual rotations each having their own true qualification. 

[[Jo...]]

Apparently Sigma values are always listed in MM regardless of the units setting.  You may find the values acceptable in mm

[[Pe...]]

Please sign in to view this quote.

This is good to know.

I have but two questions:

1) How would it be worse for a longer probe since the longer probe gets requalified on its own?  Each probe should have its own calculations?

2) What level of accuracy can I expect from RC-CAA Calibration?  This is kind of a bad question since you said the longer the probe, the worse the error, but how bad does it have to get for me to say that something is verifiably wrong with the machine?  I've come in the morning more than once to the rdsprobe adapter+sensor+broken styli lying on the table so there is definitely the possibility of damage.

For now, I will have to try the non-rc-caa qualification for this probe to see if there is better results.

[[To...]]

Please sign in to view this quote.

I think Richard is mixing up a qualification sigma results with your test results

Edited June 17

[[Ri...]]

Please sign in to view this username.

 The CAA functionality is completely different from a normal qualification. It is only doing 12 positions, and calculating the rest. 

I have always just been told that the longer the stylus system the worse the error - for CAA - normally qualified stylus systems are not affected by this. 

I cannot give you a hard number, I have seen documentation, but none of it is publishable unfortunately. 

Please sign in to view this username.

I don't think so? Lol, but who knows it's been a long week.  

[[To...]]

Please sign in to view this quote.

I assumed you were referencing the higher than normal sigma value when qualifying a CAA stylus system when Cory was talking about the variation of the results when using different styli to take a point on the same surface.