I thought I'd revive this discussion. I've searched the forums and read the other threads on using the axis of a cylinder as Datum A. I don't think they answered the question I have here.
With reference to the print below, if I use the "Level Z+ to the cylinder" guideline, then in relation to the print, Z+ is pointing to the right (presuming vector directions). Then, it seems that the Datum B plane is PARALLEL to the [piece of paper] Datum A "plane", and therefore can't constrain rotation of the Z+ plane.
Now, the engineer insists that I'm wrong because the datum callout is to the AXIS of the cylinder, which is indeed perpendicular to Datum B.
My question is, how do I achieve this in PC-DMIS? If I construct a line in the Z+ workplane from A to C, and then use that to constrain the rotation, am I not effectively replacing Datum B with Datum C? Then Datum B simply becomes the place to put the Z origin.
How would you gurus approach this?
Another issue - the Datum C hole asks for A(M) - if Datum A is merely the axis line of the cylinder, can we even say it's a feature "of size"?
Also, would you probe Datum C as a cylinder, or as a circle with sample hits?
Datum "A" (shaft) controls 4 DOF, 2 rotational and 2 axial
Datum "B" (surface?) controls 1 axial DOF
Datum "C" (hole) controls 1 rotational DOF
6 DOF, all done.
I see no other way those datums can control all 6 DOF.
CAN/MAY/MUST rule applies.
"A" can control 2 rotational and 2 axial DOF, and it MAY since they are not previously controlled, so it MUST control those 4 DOF
"B" can control 2 rotational and 1 axial DOF, but it MAY NOT control the rotational since they are already controlled, it MAY control 1 axial DOF, so it MUST control 1 axial DOF
"C" can control 2 rotational and 2 axisl DOF, but it MAY NOT control 1 of those rotational and 2 of those axial since they are already controlled, it may control 1 rotational DOF so it MUST control 1 rotational DOF.
This is for a callout of A-B-C. It all shuffles around if the callout isn't A-B-C
Of course, this is all based on proper use of GD&T.
Datum "A" (shaft) controls 4 DOF, 2 rotational and 2 axial
Datum "B" (surface?) controls 1 axial DOF
Datum "C" (hole) controls 1 rotational DOF
6 DOF, all done.
I see no other way those datums can control all 6 DOF.
CAN/MAY/MUST rule applies.
"A" can control 2 rotational and 2 axial DOF, and it MAY since they are not previously controlled, so it MUST control those 4 DOF
"B" can control 2 rotational and 1 axial DOF, but it MAY NOT control the rotational since they are already controlled, it MAY control 1 axial DOF, so it MUST control 1 axial DOF
"C" can control 2 rotational and 2 axisl DOF, but it MAY NOT control 1 of those rotational and 2 of those axial since they are already controlled, it may control 1 rotational DOF so it MUST control 1 rotational DOF.
This is for a callout of A-B-C. It all shuffles around if the callout isn't A-B-C
Of course, this is all based on proper use of GD&T.