Composite Profile question

[sendithard]

I'm questioning if the many profile callouts I see that don't have a profile section that includes a straight portion should not have a secondary datum for clocking in the secondary FCF

A good example would be the below pic from the 2009 std....IF the second FCF had AB instead of just A...wouldn't that be odd to control the tighter tolerance zone to orientation based on B? Or would you, the cmm, etc, use the basics b/w the radii centers measured parallel to B in order to control the tighter zone to B?

Thanks.

 

[Burunduk]

Depends on what one wants to achieve.
Referencing only A in the second segment of the FCF only tightens orientation in two rotational directions. Referencing A, B controls all 3 rotations to the tighter tolerance.