Position with a spanned datum?

[mikeojai]

I have a question of how to interpret a control frame.
Look at the attached image of the frame and part:

The position of datum -G-: Primary Datum -D-, Secondary Datum’s E-F, no Tertiary Datum.

Datum feature list:
Datum -D- is a face.
Datum’s –E- and –F- are dowel holes on that face.
Datum -G- is a bore thru datum -D- face.
Basics are struck off centerline of –G-, X&Y back to -E- & -F- datums
How do I calculate the position?

 

[drawoh]

mikeojai,

Your drawing would make sense to me if there were no datum[ ]G, and your true position tolerance was for the primary, secondary and tertiary datums[ ]D, E and[ ]F. Datum[ ]E would locate in X and[ ]Y. Datum[ ]F would control rotation.

The composite specification E-F implies that the two datum features work together in some unambiguous way, and I don't see such a way. Ask yourself how you would design a fixture to pick up datum[ ]E-F.

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JHG