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?
-B- isn't ignored. And it is valid! It just
geometrically can't be used to constrain rotation because it is along the same vector as the feature you're leveling through.
-A- has a Z vector, so you need to rotate to something that has an X or Y vector. Rotating from cir-cir gives you the Y vector.
Level Z, rotate to X or Y about the Z, XYZ origin. Bingbangboom.
CAN/MAY/MUST
-A- CAN and MAY/therefore MUST be leveled to the Z.
-B- has a Z vector so it CAN NOT be rotated about the Z for this alignment.
I realize I sound repetitive but I am trying to break this down for your benefit. Hopefully its helping!
-B- isn't ignored. And it is valid! It just
geometrically can't be used to constrain rotation because it is along the same vector as the feature you're leveling through.
-A- has a Z vector, so you need to rotate to something that has an X or Y vector. Rotating from cir-cir gives you the Y vector.
Level Z, rotate to X or Y about the Z, XYZ origin. Bingbangboom.
CAN/MAY/MUST
-A- CAN and MAY/therefore MUST be leveled to the Z.
-B- has a Z vector so it CAN NOT be rotated about the Z for this alignment.
I realize I sound repetitive but I am trying to break this down for your benefit. Hopefully its helping!