Hey all, I have a couple questions about how PC-DMIS handles certain datum features. I have a drawing where datum B is an external width dimension, meaning the actual datum feature would be the midplane derived from each side of the part. There is a profile callout for each side of the part from which the midplane is derived. I’ve been in this scenario many times and didn’t really think anything of it until out of genuine curiosity an engineer came up to me and asked me how it works. His question was if the midplane is derived from the features that are being inspected to that same midplane (the sides I just mentioned), why wouldn’t the software just split the difference and have the profile results be equal on both sides? This had me stumped. I know that if we were to check this part manually, we would put it in a vise and use the jaws as the surfaces for datum simulation to get the mid plane, and zero our indicator out at basic to check the profile of each surface. PC-DMIS is doing it right because it’s clearly not splitting that difference. Basically my questions are:
- Upon defining that midplane as a datum, is it deriving that location based on the highest points of the surfaces as if the part was in a vise?
- In the 2009 and 2018 standard it states that the midplane is derived from two parallel planes at minimum separation. I see in the edit window for each surface that I can choose between LSQ and Min Sep. Should I be choosing Min Sep? And what exact difference will it make?
Any insight is appreciated.
