Qualifying small star probe

[[Me...]]

Hello all,
I am having an issue with the main shaft and retaining element of my new star probe shanking against my 8mm qualification sphere.

I'm using a Duramax with an XXT TL1 head with no RDS. Trying to qualify a .5mm star probe with 5 mm long shafts.

Already tried to reduce the sphere coverage. (Actually went all the way down to 90 degrees.) The scan path never changed. Manually adjusted the stylus radius and shaft radius, scan did not change.

I feel I'm either doing something wrong or that there may be a way to reduce the scan path that I don't know.

[[Ri...]]

On an XXT, the Passive Qualification (for the bending parameters) will always be 180°. If you change the sphere coverage, all it will change is the Geometry Qualification at the end (5 points).

With the 8mm Qualification Sphere, I do not see why you would need to change the sphere coverage.

[[Th...]]

I'm curious to know how your styli might be shanking on such a small reference sphere. Are the stylus stems bending enough during qualification to contact the sphere?

[[Me...]]

The styli shafts aren't shanking. The extension (actually the M3 to M2 adapter) and retaining element are, which knocks the ruby off the qualification sphere entirely.

[[Ri...]]

That doesn't look like an 8mm qualification sphere. That looks for like the 25, but I could be wrong.

[[Th...]]

I'm not really familiar with Renishaw stylus components, but those stems look a lot shorter than 5mm. Is this like the star styli where they dimension it with a 10mm span? Based on a quick search, the closest thing on their shop I found has only 2.5mm from ball center to the bottom of the stem.

[[Me...]]

Richard, it is an 8mm ball. See the sticker on the shaft that says 7.999?

Thomas,

You are correct sir. I forgot the length spec yesterday in my frustration.(Renishaw was the only company that had the star probe I needed and only had it in M2, hence the M3 to M2 reducer. The Renishaw part number is A-5003-4011.)


The pics were to show the issue. I was hoping for some insight into changing the qualification path on the sphere.

[[Me...]]

So ultimately, the answer is a smaller Qualification sphere. Once the initial qualification is completed, I can reduce the scan path for subsequent re-qualification.

[[Ri...]]

You could try mounting a master stylii (or similar small dia stylii) in a small bimu vice or similar and create a new master sphere profile with it.
Then calibrate the star on the captive master stylus.

[[Ri...]]

I would only do that as a last resort as you have no certification on your reference sphere, so you'd just be relying on the qualification information gathered when you qualified it. That is not good enough.

I would request a custom one if this is a stylus system that you plan on using for awhile.

[[Da...]]

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You mean like this? 🙂 -> viewtopic.php?f=11&t=1403&p=9420#p9420
(And check Norberts reply also in that thread)

[[Ti...]]

Jason,

I'm looking at a very similar application now - a Duramax measuring small internal grooves. I bought Ø0.6mm threadless styli from Q-Mark (cmms.com) and made my own stylus-holder. Also bought from the same place a Ø5mm certified calibration sphere, which I only use for the Ø0.6mm styli.

For testing and experimenting, I just qualified using a carbide spherical indicator tip (like a gage ball) that I already had. I would not recommend doing that as a robust long-term process, just for experimenting with a new setup.

[[Me...]]

I was able to borrow a custom sphere from a fellow programmer in the area. They had made that sphere in their tool shop for the same reason and only used it once.

After initially qualifying the probe set on the 5mm sphere, I was easily able to modify how the probe qualifies on an 8mm sphere sticking straight up.

Thanks for all the input guys.