2nd Reference Sphere

[[Ke...]]

So, for the first time ever, in almost 20yrs of programming, I need to set up a 2nd reference sphere for short styli...

First:
I have a calibration spehere that is in good condition, but not certified - Whenever I verify results to certified masters (plugs & rings), I match the average certified values to within 0.0003mm - so, I'm leaning toward trusting and using the CMM measured values (Sphere radius & form) when entering the calibration sphere data. Does anyone with experience forsee any issues with this?

Also:
The styli that I need to use for a specific task are custom for a nominal size.
When calibrated, the calibration results for the diameter (Rx2) is 0.0035mm larger than the specified size (micrometer measurements show the size at nominal)... while this isn't necessarily a dealbreaker for the measurement task, I was considering modifying the values of the calibration sphere, to get the stylus radius/diameter closer to nominal... again, if anyone has experience with this(?)

...upon reflection, I will calibrate a new stylus to both reference spheres, for comparison, before I consider any modifications

Thanks in advance for any advice/insights.

[[Jo...]]

Setting up a disc stylus isn't really that much different than what you're doing, is it? As far as I know (at least with an XXT) you can only use the well-known workaround for creating a disc stylus system, using properly calibrated rings. You basically trick the CMM into thinking you have a 25mm sphere, when really it's a 2-dimensional, nominally 25mm disc at it's equator. And doing this is fairly common I think?

As far as the micrometer comparison goes having such a tiny amount of discrepancy wouldn't really be unheard of, especially since the number you get with a micrometer can vary slightly depending on the quality of the mic, the person using it, and the fact that you really are only getting a two-point measurement with that method.

[[Is...]]

I used to have two calibrations spheres (Ø 30 and 8 mm) then later both were replaced it by a single Ø 15 mm. now in my case there’s no need to have two calibration spheres.

Is also common to see a different qualified value than when I check the sphere in the ULM . in my case the reason of this most of the times is related to rigidity of the probe.
In some Stylus systems ZEISS is solving this welding some components of the stylus before they send it to us. The quality of the materials is very important also.

Accessories -Stylus-Systems.pdf