True position Question

You can't use C for the rotation if B is listed second with A being Z+.

B is capable of constraining K (rotation about Z) and therefore, being listed second, must do so.

There is a method an engineer can use to state that the tertiary datum rather than secondary is constraining something, but you don't show that in your notation for the position.

So, A constrains I and J rotations and Z translation.
B constrains K rotation and X translation.
C constrains nothing.
Y translation is not constrained by anything.

This is how it is written, and how it must be done. In your sketch, there is nothing for Y no matter what you use to halt the third rotation.

If B and C were perpindicular to each other, rather than parallel, then you'd be fully constrained.

Without special instructions, no datums yields to a subsequent datum.

YOU can't SAY A just does the rotations because B is more important and holds Z. The standards are not written that way.
The ENGINEER must WRITE if that is the case.

Apparently, the brain trust making Y14.5 couldn't use I, J and K like EVERYONE in the industry (I wonder if this is U.S. only and that's why I think this?), I looked this up to get it right, they use U spinning around X, V spinning around Y and W spinning around Z.

So, your FCF (I made up a tolerance since you didn't give one) of POS | Ø .014 RFS | A | B | C |
Diametral tolerance zone of .014 regardless of feature size with
A constraining U, V and Z
B constraining W and X
nothing for Y

What you are suggesting in your words, B is more important for translation but C controls the spin would be written: POS | Ø .014 RFS | A [u, v, z] | B [x] | C [w] |
Diametral tolerance zone of .014 regardless of feature size with
A constraining U, V and Z
B constraining X
C constraining W
nothing for Y


This is Y14.5-2009, sec 4.23, pg 83, with a figure 4-46 on pg 84. You (the inspector) don't get to skip B in favor of C, the engineer has to write it. Of course, that doesn't stop the engineer from wanting it and not writing it because the engineer doesn't fully understand GD&T... but I'm being crazy, engineers ALWAYS understand GD&T perfectly, that's why they make threaded holes datums and apply MMB to them, I'm being silly. (HEAVY sarcasm if you couldn't read my tone in to that lol)

You can't use C for the rotation if B is listed second with A being Z+.

B is capable of constraining K (rotation about Z) and therefore, being listed second, must do so.

There is a method an engineer can use to state that the tertiary datum rather than secondary is constraining something, but you don't show that in your notation for the position.

So, A constrains I and J rotations and Z translation.
B constrains K rotation and X translation.
C constrains nothing.
Y translation is not constrained by anything.

This is how it is written, and how it must be done. In your sketch, there is nothing for Y no matter what you use to halt the third rotation.

If B and C were perpindicular to each other, rather than parallel, then you'd be fully constrained.

Without special instructions, no datums yields to a subsequent datum.

YOU can't SAY A just does the rotations because B is more important and holds Z. The standards are not written that way.
The ENGINEER must WRITE if that is the case.

Apparently, the brain trust making Y14.5 couldn't use I, J and K like EVERYONE in the industry (I wonder if this is U.S. only and that's why I think this?), I looked this up to get it right, they use U spinning around X, V spinning around Y and W spinning around Z.

So, your FCF (I made up a tolerance since you didn't give one) of POS | Ø .014 RFS | A | B | C |
Diametral tolerance zone of .014 regardless of feature size with
A constraining U, V and Z
B constraining W and X
nothing for Y

What you are suggesting in your words, B is more important for translation but C controls the spin would be written: POS | Ø .014 RFS | A [u, v, z] | B [x] | C [w] |
Diametral tolerance zone of .014 regardless of feature size with
A constraining U, V and Z
B constraining X
C constraining W
nothing for Y


This is Y14.5-2009, sec 4.23, pg 83, with a figure 4-46 on pg 84. You (the inspector) don't get to skip B in favor of C, the engineer has to write it. Of course, that doesn't stop the engineer from wanting it and not writing it because the engineer doesn't fully understand GD&T... but I'm being crazy, engineers ALWAYS understand GD&T perfectly, that's why they make threaded holes datums and apply MMB to them, I'm being silly. (HEAVY sarcasm if you couldn't read my tone in to that lol)

Well you got also confused :P

B cannot control the K rotation as its vector is K. A constrains 3 DOF as you wrote, B does 2 (but translation in Y is not needed in this case) and C is left to constrain Rotation. For me nothing wrong with the callout just that it get a bit complicated and can confuse a bit (you and me both apparently :P )