circular hole pattern as datum 2

[rhmeng]

I know there is a lot of discussion about holes for datums, i think i read them all, still a little confused. I have this part (see pic) that has 4 thru holes that bolts go through and meet up with tapped features on a different part. is the way i have it correctly dimensioned (only talking about the thru holes, datum A is the face the holes are on)? So the virtual condition of all of these holes will be diameter .144", with respect to eachother? The mating part has the tapped features dimensioned with a virtual condition of diameter .144" so i think i am fine. I am trying to understand how to think about it, or how it would be checked. Would you have 4 .144" pins at the basic locations and then see if this part fits over the pins and if it does its ok? Any help would be great. Thanks in advance

 

[powerhound]

I'm not talking about adding notes and neither was he...or she. He/She was asking about inferring a manufacturing sequence from the GD&T on the print. In my experience it's a common thing for inexperienced machinists to think that you HAVE to produce primary, secondary, then tertiary datum features in that order. Even if it's not convenient to do so.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[MQSCI651]

In the assembly, when you use that 4 holes pattern to locate the part, it is the case. Otherwise, when you use OD to locate the part, it is not the case.