Quote Originally Posted by deadlykitten View Post
hello again, i just can't stop thinking about this ... i don't believe that there is backlash, especially because 1/4* means 0.554mm circumference length for the od of a 10" chuck, and that is huge, meaning that the C axis should be used only with the break on during drilling, and it would shake during contouring

vzshc=1/4*means that there is a missalignment in Y direction; there may also exist a missalignment in X direction, but this one can not be corected by using vzshc, so, for now, let's focus only on Y missalignmnet : for example, if there is 0.1mm Y radial excentricity, and drilling occurs at X50, then it will be required to use a C phase corection of 1/4*, and this sounds pretty realistic

so far so good ...



so, deviation is 1/4* + a bit; 1/4* may be from Y missalingment, and 'a bit' may be from the fixture tir ( because the part is re-clamped ) and/or drills buckling/bending, because of wear/length/specs

kindly
It is possible that this is a fixturing issue.
VZSHC would help a Y axis err if the holes were parallel to the Z.

I still believe it is a backlash during setup issue.
I have had this issue when setting up to re-machine features on rifle barrels which needed machined in relation to the gas port hole. We indicated across a fixture with a pin in the hole to find C0 for every part.

Hopefully he finds and shares the answer. I hadn't thought about this again at all until I checked my email and saw the reply notification. Maybe then you can think about something else.