True position reports zero for Z location on threaded holes

[[Th...]]

I’m measuring the true position of two threaded holes using the legacy true position with datum B primary and A secondary. The Y results vary, but the reported Z location is measuring zero. Nominal location being zero.

When I switch from a diametral Y/Z tolerance zone to a polar zone, Z variation appears but the drawing does not specify a projected tolerance so I don’t want that. I also changed a feature’s nominal Z from 0 to 0.100 as a test, and its actual Z then reported 0.1000.

Anyone know why this is happening? Given the datum structure, rotation is free so is Calypso forcing the feature to the perfect zero? If so, is this ok to leave like this?

Note: I’ve also tried using a bore pattern and freeing the rotation.  When I do there is variation in both Y and Z but of course TP results significantly increase since there is now another variable to include in the error. 

[[Jo...]]

Hi Thomas,

sounds like you only got a point (centerpoint circle) and not a zylinder. Thats why you only get the options circular tolerance zone (2d) or spherical (3d).

You would need (if there is a "Ø" in the tolerance field) a cylindrical tolerance zone and therefor a cylinder.

[[Th...]]

When I use a cylinder I get an even more confusion result. The majority of the reported Z values remain as zero but with every so often part I do see variation in the Z actuals. 

[[De...]]

When using threaded true position pins, I do a cylinder on the measurement area of the pin and then use the intersection of that to the plane where the hole is located as the point for the feature to be measured to.  

 

 

To the professionals: If this is a bad habit, please let me know.  It has worked well for me on several parts.  I typically do this to find true position of any hole.