Is There Such a Thing as a Clocking Datum?!?!?

[mylesmangram]

My background for this topic started off in machining for nearly a decade and a half, got laid off (thankfully), and went back to school for engineering (Industrial/mechanical). I current use the ASME Y14.5-1994 (but we are slowly transitioning to 2009). Lastly, I have a ton of blueprint reading an writing experience, but always up for learning something new from all the great people of engineers edge.

My problem: I am responsible for reviewing every print and mechanical assembly to make sore the two dace together prior to MRR meetings. We have a fairly non complex circular part (pretty much just a flange) that one of our mech engineers keeps adding a tertiary to one of the surrounding holes as a "clocking feature". There are no examples to show him except 4.4.3 in the ASME Y14.5 to show, as the holes are polarly toleranced. It is literally a 8 holed flange. Primary datum is the face. Secondary datum is the center hole. Tertiary datum is a hole that he did not feel like placing at the zero line. Has anyone seen this? I cant find it in any standard or Blue print reading and wring book to support the use of a parallel axis's for doing a simple bolt hole circle....

[Kelly_Bramble]

Primary datum is the face. Secondary datum is the center hole. Tertiary datum is a hole that he did not feel like placing at the zero line. Has anyone seen this? I cant find it in any standard or Blue print reading and wring book to support the use of a parallel axis's for doing a simple bolt hole circle....

Short answer - yes, I have likely seen this.

Had you posted an image showing the specific specifications in questions I could give a more thorough answer.

[spektre76]

Yes, I have done when designing tooling for our Main Injector. I usually make this Datum C and reference it in any FCF I may use.