Composite Positional Tolerance as Datum

[RLD89]

Is there any reason two coaxial holes with a composite positional tolerance can't be used as a Datum? To be clear, the holes are located to a DRF with one tolerance and tighter to each other with another in the composite FCF. With these two coaxial holes established, a second DFR will be established from which other features will be held. I use 1994 standard. Thanks.

 

[CheckerHater]

In general, anything may be used as a datum, but some sketch would be nice.
There is no need to disclose proprietary information, but something similar showing what is related to what.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[axym]

RLD89,

I agree with CH that anything can be used as a datum feature. There is nothing in ASME Y14.5M-1994 that disallows what you are suggesting. The tolerances on a feature (or group of features) don't affect whether or not that feature/group can be used as a datum feature. The composite position tolerance on the two coaxial holes would affect the calculations for the simulator size, if that datum feature was referenced at MMC.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca