How is Datum B constraining the Position tolerance?

Make -a- datum cylinder axis as long as humanly possible.   

This drawing is terrible. 

1: -A- datum is ambiguous as there's five interrupted cylinders.  Is the datum just the middle one, or all five features of size there?

2: -B- datum cannot be a "width" between the same vectors like that.  I agree with Neil, that -B- datum should be defined and tied to the bottom extension line of that 1.00" dimension, clarifying the -B- datum as the one planar flange.

The 1" protrusion/boss to the hub flange has no significance to B datum.  The perpendicularity should be only tied to that -B- datum flange face.

If you are getting parts that are out of spec, using A to B, reverse the datums... making B primary and A secondary, and see how the true position comes out.  give that info to dumb engineer.

Make -a- datum cylinder axis as long as humanly possible.   

This drawing is terrible. 

1: -A- datum is ambiguous as there's five interrupted cylinders.  Is the datum just the middle one, or all five features of size there?

2: -B- datum cannot be a "width" between the same vectors like that.  I agree with Neil, that -B- datum should be defined and tied to the bottom extension line of that 1.00" dimension, clarifying the -B- datum as the one planar flange.

The 1" protrusion/boss to the hub flange has no significance to B datum.  The perpendicularity should be only tied to that -B- datum flange face.

If you are getting parts that are out of spec, using A to B, reverse the datums... making B primary and A secondary, and see how the true position comes out.  give that info to dumb engineer.

Hi Louis, the datum A is just the cylinder with the datum attached to it, not the rest of the interrupted cylinders. The very intelligent engineer did update the drawing now but I still don't think its right. Attached is how he drew it. When I try to add datum B pc-dmis won't let me. Also not quite sure about the dash in between datums on the feature control frame, never seen that before.

I just checked the datums separately, but I think I should tell him that I cant check it how he has it called out. What do you think Louis?

Okay after some research looks like this is a "common datum axis" I am going to try to construct a line using the two cylinders on my cmm and use that as the datum

The datum is A-B not A|B.

You need to define Datum A and B individually, and then create a compound datum.

beautiful. Thankyou. These parts were out before but now they are wayyy inside the tolerance. Thanks be to god.