CAA 1mm probe gives poor CAA qualification`

[[Pa...]]

Have a 1x20mm single point star probe coming off a 50mm down extension. Head is VAST XXT using RDS-CAA. The best sigma I can get is .0007. Have changed the probe, extension, and adapter plate in hopes of doing better. No luck. My 4 other CAA star probes sigma .0001-.0003 and extensions are all the same or longer than this probe.
The only reason I can see for the sigma differences is this probe is 1mm, others 3 & 5mm. But I don't understand why that should matter. Anyone have an explanation? Is this the best I can expect? Any way to improve my 1x20 CAA qualification? THX.

[[To...]]

Do you have another 1mm stylus you can test? Other than making sure everything is tight and clean. Check the adapter plate for any chips or FOD . Also check the inside of the XXT for FOD though you're not having any issues with your other stylus systems.

[[Pa...]]

ok thanks Tom, I have tried these suggestions, but no better. Maybe .0007 is the best I can expect? but if that the case, why does a 3mm ball with same extensions come in at .0002? Does ball size make a difference with RDS-CAA?

[[To...]]

I honestly don't believe the ball size has anything to do with how well it qualifies. If you have a microscope, you might want to take a look to see if there is a defect, crack or some other anomaly that could be causing you grief.

[[An...]]

I calibrate every probe that has less than 2mm in diameter, with a 8mm gauge ball!
Have also made the experience several times when I kalipriert small buttons with a 25mm ball, which have increased the sigma values.

[[Da...]]

It's been a long time since I had a XXT so this might not apply, Check the rigidity values in Probe quality. If the are very low, try reducing the gaging pressure. I think the xxt had a 3 step pressure adjustment.try the "sensitive setting " for calibration. You MAY also be shanking ever so slightly. Double check !

The reason a 3 mm probe checkds good and 1 mm doesn't has to do with the shank diameter and length. If you can get by with a shorter length ( new probe) it will probably check better.

[[Ca...]]

I have one of these to visual probes for cleanliness.

https://www.mscdirect.com/product/details/63722326

[[Da...]]

Any resolution on this Paul ?

[[To...]]

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I never get anything greater than 2 microns (.000080") on any size probe, even a 1mm x 20mm on a 50mm extension on a 30mm diameter reference sphere.

[[Da...]]

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While that is true most of the time, once you get into extreme length to diameter ratios with the probe, the flexibility numbers get so low that the probe won't repeat. I don't know his probe dimensions , so if he's getting bad numbers then this might be something to look at. I am using an XT and we had trouble with a 1.5 mm probe that 40 mm long, carbide shaft at .8mm diameter. We retired it and several back up probes cause the were unstable.

[[To...]]

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I understand. I was just trying to explain that the stylus system that Paul was using should have been able to produce better results. However, after just re-reading his post, I noticed he said it was a "star" which means it could be an assembly, as opposed to a "fixed star", and if the star is not firmly tightened, it could be moving during the qualification.

[[Gr...]]

We have two Zeiss Cmm's, a Contura G2 RDS Vast XXT TL1 Head and an ACCURA 2 RDS CAA Vast XXT TL3 head.
I have attached 3 photos one our Frankenstein Stylus, two the quality after qualification (results in inch@5 decimal places) and three the behavior setup using a 8mm reference sphere.
The stylus itself is carbide @ 0.6mm.
As you can see we do not have a problem with sigma.
Six years ago we had a very similar problem which turned out to be the Vast XXT head.

Special Stylus Assembly.jpgSetupBehavior.jpgQuality.jpg

[[Pa...]]

Thank you all. I found a 12mm ball to qualify the 1mm star probe. While starting to qualify as RDS-CAA, I noticed the routine was measuring the twelve positions "bend map of the probe" (that's what I call it anyway) using fewer points than my usual 26mm sphere. I'm hoping that's good (calypso able to get a better hack at the bending characteristics around the sphere maybe?). But I did not finish due to end of month shipments. Should get back to shortly.

[[Pa...]]

Well I calibrated the 1mm star with the 12mm sphere and got no better results, .0007-.0008 sigma. There's nothing left to replace as I've tried a new probe, new 40mm extension out and new adaptor plate. Maybe have to rebuild with no extension or qualify passively?

[[To...]]

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Is this just a single down probe in a star adapter?

The problem with going without the extension is the 1mm probe is only 20mm long. Zeiss would like a minimum stylus length of 30mm, so you're not introducing another variable.

I don't know if any of us mentioned but make sure the inside of the XXT sensor is clean. I recently had an issue with a customer that was caused by some FOD inside where the adapter plate sits.

What were sigma values on the MasterProbe and other CAA stylus systems.

[[Pa...]]

Attached is file.
Down 50mm star adaptor, then out with a 40mm extension and 1x20mm probe. My master sigma is always under .0001 and CAA sigmas .0002 or lower.

[[Da...]]

Ant chance you could put another probe going the opposite direction to even out the weight ? I've always had better results with a balanced probe set up.

[[Pa...]]

I'd considered that but 60mm at 180 degrees will back me into things. Would something of the same weight but shorter work as well? I can't see why not (I say that as though I have one of those handy:).