Two tolerance zones to a single datum axis A-B 1

[greenimi]

I have a question for the group: the part I would like to talk about it’s a shaft with a weird thru irregular feature. The axis of one radius is datum A and the axis of the other radius is datum B.
If you have the centerline on the part:
Datum feature A, radius -left side from the centerline – will generate a datum axis on the other side of CL—on the right side.
And similar, datum feature B (radius, datum feature on the right side of CL) will generate a datum axis on the left side. See sketch with red and blue centerlines.
It’s a coaxial control which locates and orients two tolerance zones to a single datum axis.
I was told this is the design intent and reflects the functionality of the product (there is a mating part which go inside this irregular feature and the mating part has the same construction).
See the profile callouts depicted:
Datum feature A: profile .004 wrt A-B
Datum feature B: profile .004 wrt A-B
Datum feature C: profile .003 wrt A-B
Profile of bottom surface wrt A-B and C
The questions I have:
1.) Is those valid GD&T callouts? I think so, but I just want to double check.
2.) How we can measure the profile callout? How to establish DRF between A-B on the CMM, for example?
3.) Could be a common misunderstanding in the industry, but both datum feature A and B are referencing a location back to themselves. I am almost sure (but not convinced, and that’s the purpose of the question) that is not the case here, and the datum feature A and B are NOT referencing back to themselves. Any help to shoot some lights here?
Thank you

 

[pmarc]

I stand corrected. Primary datum derived from datum features A-B constrains 5 DOFs.

 

[CheckerHater]

Thank you bxbzq,

Glad to see that I was not alone. Two parallel cylinders set side-by-side really establish enough of a datum framework, so we don't really need datum C.

Now, what's your opinion on "common sense" rule that states: "A profile control should not be applied to the surfaces it references as datum features"?

 

[bxbzq]

CH,
A while ago I read a thread in this forum discussing the self referencing profile control. From my fuzzy memory, the conclusion (?) was self referencing is legal, but not recommended. The profile tolerance zone applied to the datum feature is cut in half.

 

[CheckerHater]

Yes, I guess it was this thread

Now I just have to convince myself that we need datum at all.