I hope this is as simple as I think it is. I have a part the calls out the true position of a 5/16-18 ID threaded hole with MMC. I think that the MMC should come off of the minor diameter. Onr of the owners and the QA manager think it should come off of the pitch diameter. Other than the fact we don't have a good way to measure the pitch diameter in house I think they are wrong. What are the prevailing winds on minor or pitch for MMC on a ID threaded hole?
IMO it is one of those things that look "cool" on the print, but is very difficult, or impossable to measure. In order for you to measure this you need the minor diameter in order to calculate MMC, BUT if you do not measure exactly on the crest of the minor diameter then any bonus may be questioned.
I have used the locators in the past(before PC-DMIS), but now I hit on the threads. I have done several tests and have confidance that the 2 methods were within .0015" of one another.
IMO it is one of those things that look "cool" on the print, but is very difficult, or impossable to measure. In order for you to measure this you need the minor diameter in order to calculate MMC, BUT if you do not measure exactly on the crest of the minor diameter then any bonus may be questioned.
I have used the locators in the past(before PC-DMIS), but now I hit on the threads. I have done several tests and have confidance that the 2 methods were within .0015" of one another.
