Wrong position for cylinder

[RafaelMW]

Hi everyone, it's my first post here.
I've found this forum when i was looking for some help and it has a lot of good content.

I need to measure a position of a cylinder but i can´t do it right.
Here it's an image of the position that i need to measure (I use Polyworks to do it).

If i use only Datum B it works right but when i put datum A the program calculates it wrong.

I believe i cannot use Datum A because i don't have a middle point for cylinder C.

I've tried to find in the ASTM something about this to discuss with the responsible engineer, but can't find it.

Somebody could help me?

 

[Ryan6338]

There's no problem with using datum A as a the primary datum on the 45.25 hole. Datum A will constrain perpendicularity of the hole to the datum plane. Datum B will then constrain one translational degree of freedom of the hole.

Ryan.

 

[SDETERS]

My first move using Polyworks is to call them, they have amazing customer support. How are you generating your Center plance for your Datum "A" in Polyworks?

 

[RafaelMW]

Doing more tests i found a possible solution.

Probably the problem is because Datum A is too short and far from the Datum C, so it projects his misalignment.

I asked to add a Datum D, and got much more realistic results.