Stylus Standard Deviation

[[Jo...]]

I wanted to get some thoughts on this stylus system. I was informed that it has always qualified at .010mm or higher. It has recently been providing inaccurate results. The horizontal shaft is ~8 inches long.

Today, we inspected the tips, and they appear to be in good condition (no visible flat spots or aluminum buildup under microscope). We verified all connections are tight. Both tips qualify at the same sigma value and radius (.005 mm oversized). We then tested qualifying each of the tips at a 20-30% probing dynamic, and that yielded .001mm. We also tested adding a counterbalance to the system, and that made no difference at the 100% probing dynamic.

Does this seem right to you guys? Could there be something else causing issues? I have limited experience with stylus systems like this. We also have a couple other setups like this, and they qualify around the same sigma value. My leading theory is simply that the shaft length causes it to “shake” during probing, so the lower dynamic slows this movement down, allowing for more stability.

[[Ma...]]

I would suggest a counterweight.

[[Jo...]]

what happens when you build maximum compact with just the two styli and test them seperatly?

Would be a good starting point knowing that this gives the expected results before looking further.

You could then start rebuilding link for link, maybe that shows a weak link (a link with more flex than expected).

 

I dont know the system so just speculating here, but it could also be wear of the modul itself. Meaning it was once "strong" enough to support the weight but isnt anymore.

Edited 11 hours ago

[[Ri...]]

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Yep, for that length and probable weight, I would say a 40mm extension and about 50g of weight will work.

I have a similar probe with this configuration.

[[A...]]

I recommend a counter weight as well along with taking it apart and cleaning the threads of all connections. The threads usually get me. I also find it ok to probe at 1% dynamics if needed.

[[Ch...]]

We have a stylus system that is very close to that one.  It often qualifies between .0005 and .0010.  We do use a counter weight, but it still doesn't qualify that well.  We only use it for stuff with loose tolerance since I know its not that accurate.  

 

HOWEVER, I would suggest trying a different adaptor plate as well.  The XTR adaptor plates are more complicated which just means that there is more that can go wrong.  Which sucks, cause those things are $$$.  

[[Ja...]]

For me, I would say this stylus system introduces two significant undesirables - Length and stiffness.

Length - The longer the probing system (with all things being equal), the more error will be introduced. Unfortunately that’s just the way physics works. The shorter you can make your stylus system the better.

Stiffness – The longer the build-up, the more important it becomes to have the extensions be as stiff as possible. The 20mm Ø extensions are stiffer than the 11mm Ø extensions.

Suggestions – 1) Is it possible to remove the vertical extension and cube, then mount the horizontal extension to the cube on the plate? This would reduce length and weight. I’ve done this on a few of our systems and it always helps. 2) Can you replace the 11mm Ø extension with a 20mm? That would help with stiffness. And use the shortest extension possible. 3) Sometimes you can gain a little bit by changing the probing pressure. Sometimes more is better, and sometimes less is better. Experiment. 4) As others have suggested, a counterbalance may get you a little bit too. 5) Slower speeds may also get you a little.

You’re still going to have a significant sigma value so I would also suggest doing an R&R study using the artifact so you know how much measurement error the system is going to introduce in each of the directions, and the diameter. If I remember right, Zeiss recommends a 10-run R&R. I usually do a 5 or 6-run.

[[Jo...]]

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Do you get those results with 100% probing dynamic?

 

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When I tested it with a counterweight, it made minimal difference. I will likely check the weight and test again. It is currently yielding acceptable results, but I need to do a short R&R run to validate those results on a known specimen.

 

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I really like this approach. I had not considered testing each section of the system.

 

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We need the clearance added with the vertical extension and the 11mm diameter of the horizontal extension.

 

Sounds like the initial plan will be to test each piece of the system and find the weak point. Then I will add a counterweight to the system. If all items check fine, but the entire system still yields bad results at 100% dynamic, is it reasonable/acceptable to lower the probing dynamic for something like this?

[[Ri...]]

My current build.

This probe is 6 inches long, so you would need about a 60mm extension for the counterweight (best guess).

If you balance the stylus on the tips of two fingers after its built, you will have a good idea if it is balanced.

I place two fingers under the Adaptor far apart as close to center as possible, then let the stylus hang.