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?
I believe if it is not specified, pitch diameter is used.
In practice, if it is minor diameter (for internal) you will need to gage the diameter with something other than the CMM (gage pin?).
I actually never apply MMC to threaded holes. If it is in tolerance without adding the MMC bonus, great. If not, I note that it is not possible to measure the diameter (it's always pitch diameter here) so it is not possible to report if it is in tolerance.
By 'not possible' I mean that it is not possible for me to measure it with the tools I have at my disposal. Obviously, it is possible for someone, somewhere, with better tools.
I believe if it is not specified, pitch diameter is used.
In practice, if it is minor diameter (for internal) you will need to gage the diameter with something other than the CMM (gage pin?).
I actually never apply MMC to threaded holes. If it is in tolerance without adding the MMC bonus, great. If not, I note that it is not possible to measure the diameter (it's always pitch diameter here) so it is not possible to report if it is in tolerance.
By 'not possible' I mean that it is not possible for me to measure it with the tools I have at my disposal. Obviously, it is possible for someone, somewhere, with better tools.
