Parallel datum on an irregular surface

[NL8]

Greetings all,

GDT veterans, how would you handle the situation below:

I'm trying to use a parallel call out for the faces of the two flanges circled in red on the attached drawing. I want them to be parallel to the face circled in blue and perpendicular to the face circled in green. The perpendicular call out is easy. My problem comes in the fact that the theoretical surface is straight and true but the actual surface has ribs, ripples, and other defects that could and would cause misalignment to my actual intention. What would you recommend as a better datum surface?

Joe Hasik, CSWP
SW 08 x64, SP 3.0
Dell T3400
Intel Core2 Quad
Q6700 2.66 GHz
3.93 GB RAM
NVIDIA Quadro FX 4600

 

[TheTick]

Use datum targets to define datum.

 

[Xplicator]

What he said, but remember if you use targets as your primary you should always include secondary and tertiary as well to lock in 6 DOF and for R&R.