Stylus Radius after Qualification

[[Da...]]

I recently installed a new 100mm shaft with 3mm ruby ball. The shaft is 50mm with a 50mm extension.
It keeps reading a 1.875 set ring as 1.8741 so I requalified it and I see the sigma is .0011mm ( I remember being told it should be less than .001mm) And it also changed the radius to 1.4742. Is this what is causing the issue? Why is it recording the wrong radius? I changed it in stylus geometry but when I qualified it, it changed back to this.

Is the sigma on the reference sphere too high as well?
The masterprobe shows a sigma of .001mm as well. Is that the issue?

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[[Ja...]]

The sigma value for the master is too high to start with. More than likely it's either a cleanliness issue or something isn't tight. As for the 3mm stylus system, part of your problem is having an extension screwed into another extension. You'd be better off with a single 100mm extension rather than two 50s. Keeping the number of connections on any stylus system to a minimum is the best way to go.

[[Da...]]

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Jack,
Understood...I will add a 100mm x 3mm to my wishlist.
I wiped off the masterprobe and reference sphere and ran ref. sphere position again and now the sigma is much better.
Ran the qualification on the 100mm x3mm probe and it is still recording the radius undersized and sigma at .0014. Until I am able to get a single 100mm shaft, what else can I do to improve this?

[[Da...]]

Ran the qualification a couple more times and now the radius is closer (says 1.4912) but the sigma is worse (.0019)

Also, can someone explain the x y and z under the stylus geometry? If it is a straight down probe, wouldnt the x and y be zero? None of my straight down probes are zero, so maybe not. I just dont understand what it means.

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[[Ke...]]

Could you post a picture of the stylus in question? That may help us figure out or understand more of what is going on

[[Da...]]

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Here you go.

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[[Ke...]]

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I am going to respond to this in a point by point fashion, as I feel it will make my responses a bit easier to read and respond to:

I recently installed a new 100mm shaft with 3mm ruby ball. The shaft is 50mm with a 50mm extension.
Check that the connections are tight and that the extensions are not cracked, though this can be more difficult to do and detect with XXT styli.

It keeps reading a 1.875 set ring as 1.8741 so I requalified it and I see the sigma is .0011mm ( I remember being told it should be less than .001mm).
A 22 micron difference on a ring gage could be explained by a number of factors such as measuring strategy, filtering, and cleanliness, so this in itself does not cause me immediate concern for the probe being bad, I would set it aside and check other things first, then review the measuring strategy and such. A sigma being under 0.001mm is fantastic, however I usually set tolerances on Sigma to 0.002mm with no issue, and have gone as high as 0.005mm for some cases without issue. Overall, I would not even look twice if a probe qualified with 0.0011mm Sigma (other than the MasterProbe, where we typically see submicron sigma)

And it also changed the radius to 1.4742. Is this what is causing the issue? Why is it recording the wrong radius? I changed it in stylus geometry but when I qualified it, it changed back to this.
The Radius reported there updates when it measures to show the measured value, so it is entirely possible that this is not the "wrong" radius, but the actual radius of the probe. This radius is farther off than we usually see from nominal, but is not unheard of, especially depending on the manufacturer. What is the radius reported when your MasterProbe calibrates? the MasterProbe being far off nominal (2.5mm radius) would potentially indicate a ref sphere size being off, though this would be seen in all of the probes you qualify, not just one. Do you have more than 1 reference sphere?

Is the sigma on the reference sphere too high as well?
I dont often check the Sigma on ref spheres, but 0.001mm seems reasonable from what I recall.

The masterprobe shows a sigma of .001mm as well. Is that the issue?
I typically see sub-micron Sigma on Masterprobes, but if I encountered an XXT system with a sigma of 0.001mm I would not be concerned unless I saw indication of issues on other probes. Is this new down probe the only probe you are having issues with?

[[Ke...]]

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Thank you,
I dont see anything obvious, so I would say check the two joints are tight(be careful, it can be easy to damage the extension during tightening if you are not careful),check the extension for cracks, and make sure the probe and ref sphere are clean (seems they likely are, but I am a fan of doublechecking)

[[Ke...]]

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In this case you have a good setup, a single extension and a single probe. Getting a single probe that is as long as the combined probe and extension would be a problem, as it would be rather flexible and most likely negatively impact results. A shorter probe might be better, if it were viable, as you would have less length of the thin probe shaft reducing stiffness, but this setup should be fine.

[[Th...]]

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The XYZ values are, I believe, offsets from the qualified location of the mater probe. I don't expect to ever see a stylus that is perfectly vertically offset, but the X seems kind of high.

[[Da...]]

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Thank you for the detailed response!

Connections are all tight.

The reason I checked the ring gage was because I have a part with a really tight tolerance that measures good with the bore gage that production is using, but the CMM is getting it .0015" under. So I checked a ring gage with this probe and with other probes, and all of the other probes are within .0005" from what it should be, except this one which initially was also about .0015" under, so I thought "oh, that explains it." After cleaning and tightening everything, the ring gage reads closer but still .0009" under as stated above.

When you say "when the master probe calibrates," do you mean the radius of the masterprobe after running "ref. sphere position"? Or is there a way to actually calibrate the master probe? It is currently showing 2.5mm exactly.

[[Ow...]]

I'm guessing cracked carbon fiber extension/probe shaft or loose ball attached to the shaft. You probably won't be able to see a crack or feel the ball loose, so try a different probe or put the 3MM on without the extension and see if it is still bad.

That said, an XXT has a probe and extension length of max 150MM and a weight limit of max 15G and it might be less on an RDS head? ? ?
Does that 3MM stylus have a Tungsten Carbide shaft? They weigh more than carbon fiber and that could be contributing to the issue as well.

[[Ke...]]

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Yes, the Radius after running Ref Sphere position is what I was after. If it is 2.5mm exactly, then your reference sphere is not the issue. And if you are able to measure the ring gage with other probes (that was going to be one of my checks I suggested for troubleshooting, you beat me to it which is great) and get consistent results, then things are pointing towards this configuration/stylus system being the issue. The fact that cleaning and tightening made such a big difference indicates that one of those two was an issue with the probe, but you are still seeing fairly high values comparatively.
Who made the probe? And do you have spare components (probe, extension, adapter plate) that you could try exchanging to see if you can find the culprit? If so, I would start by exchanging the probe and see if that improves, if not try the extension, then the adapter plate. Hopefully one of those will be the issue and exchanging will bring you back to expected values

[[Da...]]

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I can only speculate: damaged plate/extension/styli.

[[Da...]]

I removed the extension and my sigma is .0004 and radius is 1.5002. Ring gage reads almost perfect.

So it would seem the extension was the issue. However, this extension was brand new. We bought it awhile back but never needed it until now so it has never been used. I do not have any other extensions to test it with. Do you guys think the extension is faulty? I do not do the ordering, and we go thru a distributor who sometimes provides Zeiss and sometimes Q-Mark.

[[Ke...]]

Those results would certainly indicate that the extension was probably the issue.

[[Da...]]

Please keep in mind, that the stylus radius shown is not the actual stylus radius but the effective radius. It is the radius of the whole system probe/extension/stylus including the stiffness as detected by the calibration process to determine a "switch deflection".

For example, changing the length of your extension has a great influence on the determined effective stylus radius, even when it is the exact same ball.

The effective radius will always differ more or less from the actual stylus size. Most likely, an ordered 3 mm stylus will have an actual diameter of 3,000 with a very tight tolerance, but the effective diameter will be different.

[[Ri...]]

Something I have seen too many users do when building a stylus, whether its for an XT, XTR or XXT setup.
Using your extension as an example, too many place a tool in a hole at one end of the extension (lets say near the point of connection to the sensor) and then tighten the stylus to the extension.
This can cause twist in the extension, possibly fracturing the shaft of the extension and or loosening of the bonding agent for the steel end pieces on the extension.

Assembling styli to any non-solid extension should always use the holes closest to each other, example, where the stylus connects to the extension.

I now return you to your regularly schedule day. 😎

[[Da...]]

What others said about being carefull about not to twist extensions.
For 5 mm diameter (XXT) you could use https://shop.metrology.zeiss.de/INTERSH ... 9-0026-000, or something similar.

[[Da...]]

Did you check the collar that secures the XXT head to the swivel knuckle? They can work loose sometimes.