Since we have changed the subject of Keith's original post, let us continue on with the new one. I sent E-mail to ASME, please read below and discuss. May I start by saying the CMM has the ability to create a perfect situation based on the datum features off the part regardless of irregularities. True they are most likely not perfect but the CMM makes them so and all deviation rests on the remaining features. I understand the point of simulating the datum structure and then checking the location of the actual datums. However, GD&T as I understand it and what our customers want to know is where do the remaining part features lie in relation to the actual datums on the part. How far off is a particular hole from the actual positions of ABC on the part? Is that not the question our customers ask of us by saying check this hole back to ABC?

Regards,

Geoff
Sr. CMM Programmer
Lapeer Metal Stamping
LMS Metrology Lab
Lapeer, MI

ASME.doc
Letter to ASME (23,552 bytes)