datum question

[bxbzq]

Hi gents,

Please see sketch as attached. In this application, the 2 rows of pin hole serving as datum feature only constrain 2 degrees of freedom. Specifically, during assembly there will be 6 pins inserting half way into the holes. The exposing portions of the pins form the basic distance 112. Part being assembled can slide in between the 2 rows of pins and is stopped by the bottom edge, datum feature C.
In this application, how should I specify datum feature B, option #1 or #2, or something else?

Thanks

 

[CheckerHater]

Imagine that instead of rows of pins you have groove in your part.

You can directly tolerance dim 112. This will fall into definition of "irregular feature of size". See ASME Y14.5-2009 Para 4.17, Fig. 4-35

 

[greenimi]

Why not using datum target (B1, B2, B3, B4, B5 and B6 = contact points between the side of the pins and the mating part)?
Why "the above solution" is NOT functionally feasible or cannot be used to show GD and T literacy?

 

[bxbzq]

CheckerHater,
I think either 120 or 112 has to be reference dimension. Do you agree?

Greenimi,
Your suggestion is very interesting, but I would like to hear others opinion.

 

[CheckerHater]

I think either 120 or 112 has to be reference dimension. Do you agree?

Yes. In fact, 112 may not even be dimension per se, but simply FOS datum designation without numeric value.

Using irregular FOS is relatively new idea, so I believe opinions may split on that one.