Movable datum targets

[Garland23]

I've rarely seen movable datum targets in my work, so this might be just an academic question. Here is an example from a well-known GD&T textbook (Krulikowski) that shows a pair of movable targets hyphenated with the diagonal B1-B2 datum targets. On the other hand, the Y14.5 standard shows a very similar idea here but they have the movable targets separate from the diagonal targets.

Which do you think is correct: |A|B|C| or |A|B-C|

Or am I missing something that makes them different scenarios?

 

[greenimi]

I would go with the example from Y14.5.
Not really sure it is a good idea to combine movable datum target as a common datum with the non movable ones. It is the same idea that is probably not a good idea to combine MMC with RFS on a common datum feature like |B(M)-C|
maybe (B-C| or |B(M)-C(M)| but not a combination of those.

 

[3DDave]

In plane rotation in both cases is managed by the simultaneous application of B and C. Because Y14.5 doesn't have a way to separate out contributions but by the tedious Custom DRF system they cannot use:

[A (planar orientation, location) |B-C (planar orientation) | B (axis location)]

In the examples the final contact points with B are not determined until there is contact with C, so B-C makes sense, but some see the FCF as a step-by-step shop floor instruction and not necessarily the order of application of geometric controls.