What a great discussion!

It seems as though many of us feel that using MMC on threaded holes is a misapplication of MMC. Proving a hole to be good using thread and plug gaging, and measuring the location using RFS is the way we do it.

At our small shop we have allot of Parts, and allot of different size taped holes, with many holes per part. I don't see how probing the inside of a threaded hole can provide adequate accuracy - especially with manual CMM's (such as ours) - but lord knows I could be wrong. Since the self-locating pins are too expensive for my budget, I use Taps, Cut off the ends so I have ~1" of threads, and grind down the O.D. so that it doesn't cut upon insertion. We have excellent repeatability using these pins, and their relatively cheap.

Of course the bottom line is whether or not the customer will accept your parts, and ultimately, your measuring system. Using RFS in place of MMC is, I feel, Justifiable.

Just my 2 cents -

Keith Walter
Quality Manager - CMM Programer
Devonshire Mfg Inc