I've been asked to add the calibration of ring gages to our scope. Is it valid to calibrate a class X (or lesser grade) ring gage with a with a CMM? I don't think we would be able to do this. The CMM is a Tesa Micro-Hite3D with a resolution of 0.00001". The repeatability of the CMM is 0.000078" with an uncertainty of 3.5 micrometers. Based on the repeatability of the CMM it looks as though we would only be able to do class Z & ZZ. We might be able to do class X above 2.51" and Y above .825". But some opinions (boss) are that we go by the resolution of the CMM to determine which class of rings we can do. Any input would be helpful.
A key question is what is the tolerances you are trying to measure with the rings. Were they bought at those classes because you need them, or because they were handy. Remember, calibration at the ring gage tolerances require technique - I like to refer to it as "white glove" calibration. You can't just whip them into a CMM, much like one may calibrate a caliper with gage blocks. They must be stabilized to temperature. clean, not influenced by the temperature of the person's hands touching them. But, that is if you
need that tight of tolerance.
By the way, you cannot use the resolution of any device to determine anything. Just because its numbers show up, doesn't mean it measures that accurately in use (ever use a calculator to divide up a tip at a restaurant? What about those fractional cents?) That is why we do gage R&R to find the real resolution in the hands of the practitioners on the parts in question. For example, the CMM may read its artifact that well, but, a part wobbling in a crappy fixture (I would like to say I am exaggerating for effect, but in many cases it is not an exaggeration) will not truly be that accurate. How were you going to fixture the ring? Your "Bat-sense" (retro reference) is probably right - it may not be a good idea to calibrate ring gages in a CMM.
But, remember: the most correct answer to any question is "It depends."
