Gentlemen,

A lively discussion to be sure!

John R. - I agree that fig. 5-53 on pg 149 of Y14.5M-1994 is a good, and perhaps a more straight forward approach to controlling the location of these two holes, although ASME's example adds some tol. for the holes to move together as a unit (T.P. | 0.2 m | A | B) and mine does not. Therefore, stating "Two Coaxial Holes" with "T.P. | 0.1 m", and using "A-B" as primary datum in the FCF achieve the same thing. My customer has simply disallowed the additional [0.2mmc] tolerance.

Duane - As to where do you establish the Datum axis - The axis in my example is the "perfect" construct from C and the two mounting holes. The position of each hole is referenced to this perfect axis, as toleranced in the FCF.

Having talked to my customer's engineer and senior GD&T expert about my concerns, as well as some issues that you all have helped me to see, they have concluded that this method is legal per ASME, and achieves the desired results. Thanks everyone for your insights.

VIVA LA GD&T!!

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keith walter
manager, quality / cmm programer
devonshire manufacturing inc
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