There's no rule saying that the primary datum must be perpendicular to a position tolerance zone. Datums are simply about constraining degrees of freedom, so that seems to be correct here.
My comment would be that datum C isn't needed. You've already got a pair of holes tagged as datum B, so...
It looks like the pertinent standard would be ASME Y14.2 (link below; scroll toward the middle of that page). I don't have a copy in front of me, but it should be mentioned in that one or maybe Y14.3.
https://www.asme.org/codes-standards/y14-standards
It looks like the pertinent standard would be ASME Y14.2 (link below; scroll toward the middle of that page). I don't have a copy in front of me, but it should be mentioned in that one or maybe Y14.3.
https://www.asme.org/codes-standards/y14-standards
To the OP.... are we to assume that the question is about a callout that references A, B, and C in that order?
If not, then most of the replies above won't apply.
CheckerHater, there's no concern about that because the OP stated that we are "asked to measure true position of all three holes, with respect to datums A | B | C."
No number given, but we get the intent.
It shouldn't be an issue, really. This is a foundational idea in GD&T and there are a lot of resources to back up the idea that there's no accumulation of tolerances across those three.
That might be a good suggestion since the OP did say that we are to assume that "the entire profile bends when that surface is bent and not just that bottom surface."
Or another workaround would be to use the I modifier upon the size callout.
Thank you belanger, pmarc, and greenimi for helping on my question. So essentially, CZ takes any callout and elevates it to a location (and orientation) control. I should have just believed Ryan when that idea first appeared above!
Belanger, yes that's the question I was trying to articulate. Since CZ (in ISO) makes the orientation and location locked among the group, it apparently becomes position in that case. Others can jump in if I'm wrong here.
Still not sure that I like it, but I can live with it :)
I asked all this to see if it would be legal per ISO to use perpendicularity with CZ upon a group of features. According to the "letter of the law" in the quote you gave from ISO, it appears that that would be allowed.
But it doesn't sit right with me for perpendicularity to take on the role...
Greenimi,
"Where CZ is indicated in tolerance indicator all the related individual tolerance zones shall be constrained in location and in orientation amongst themselves"
However, based on that do you think ISO should allow perp with CZ to be used on a pattern of holes? As you say, it would constrain the perp tolerance zones for orientation and location. By doing that it could replace position (assuming that it's positioning the holes among themselves, not to...
Pmarc, I claimed that perpendicularity can't be used to locate multiple surfaces to each other based on the idea that perpendicularity can't be used on a group of holes to locate them to each other (like composite position would).
But I see your point that flatness CZ could logically extend to...
Burunduk, here's why I said not. If the drawing states 1.40625+/-.01111 then the designer wants that to be measured to at least the 5th decimal place (then 10% more or whatever).
But if the drawing states 1.40625+/-.01000 then we only measure to at least the 2nd decimal place (well, 3rd place...
This confuses me. Is your thinking simply because the tolerance of +/- .01000 coincidentally has three zeros after that .01?
What if it were 1.40625+/-.01111? Would we still say the measurement accuracy only goes to the 3rd decimal? I presume not, so why do zeros get shortchanged?
I know...
I don't think perpendicularity can be used with CZ. It's true that those surfaces are only related to the given datum(s) in a perpendicular manner, but the problem is that it's trying to also locate them to each other, which is something the perpendicularity symbol can't do.
In ASME the profile...
