Check my GD&T please 1

[mkubiak]

I have attached a portion of a drawing I am making at work. No one at work knows any GD&T so I am asking you to critique. My main question is: How do I use the mounting holes (4 outside corner holes) as datums, but also dimension their position using GD&T. Like most of you know, everyone is convinced they know GD&T, but you'll get 5 different answers from 5 different people. Any help is appreciated.

 

[CheckerHater]

You will only need 2 points for B and one point for C

 

[Michael854]

Yes...I agree you only need 3-2-1.
But, is 3-3-3 illegal on a rigid part?
I was asked to explain based on interpretation of the standard.

I think it is illegal based on chapter 4...just like I think the 4 RFS pattern datum feature is illegal.

The reason...we can't draw a drf on a rigid part with the 3-3-3.

 

[CheckerHater]

Yes, it's murky to say the least.

This is why RFS is usually limited to part being fixtured in a chuck or collet in the way we more or less understand what's going on.

It may be possible to devise some magic fixture grabbing 4 hole pattern at RMB/RFS, but it would be, as Belager put it,"impractical"