Basic Dimensions on Machining Prints

[markro]

Attached are the prints for the part in question, especially the machining print. We recently had a problem with the area between N and P not cleaning up, but the program still showed the profile (from P to M) as being good. I talked with our customer who still runs these parts and they said we are not locking the part down in space by using both the 30.5mm basic dimension (which contributes to datum F) AND using the 2.3mm basic dimension which is from datum C to datum E. Because we were not adding the dimensions together, we ended up with parts with datum F more than a millimeter from where it should be.

I do not understand this. It would seem we are locking the part down in space using the alignment which incorporates Datum C (our cmm fixture uses pins for datum A (the underside of the part), datum B4 and B5 and datum C6. We run an alignment program using these pins and then run the parts for the rest of the day using the alignment). We do not usually have the 30.5mm dimension show up on our report since it is a basic dimension, and, to start with, we are going to begin to do so to make sure datum F is not getting too far away from the 18mm hole. My thinking is, if the 2.3mm dimension ever changes, the 30.5mm dimension will change as well. The main question is, going forward, to try and alleviate the problem we had, how important is the 2.3mm dimension, or as our customer puts it, the 2.3mm dimension PLUS the 30.5 dimension?

Thank you.

 

[Marc]

NOTE: The attached drawings in the first post which started this discussion thread *may* be proprietary and traceable. I have therefore deleted the attachments as a precaution - Deleting the first post starting a thread would delete the entire thread, so only the attachments have been deleted. The original poster may re-attach the prints to a follow-up post. I consider this fair warning to prevent a potential problem here.