96 Arrow 500

Hi
I run a arrow 500 Acramatic 2100 control. Mainly produce mold parts
Recently I did a job were a block was ground square I picked it up in center. Did some milling found out I was of center
Did some tests.
If I machine the complete block profile an say a bore the bore is perfectly in center
If I take a ground block indicate it in center mill a bore it is off center in x by .002 and y .001
Take the same block indicate it in center shift my x and y mill bore I is good
What could be causing this

Thanks Joe

Joe, I would either have someone run an X-Y, Z-Y, Z-X Renishaw QC20-W Ballbar ( example: https://www.youtube.com/watch?v=qKF99g_mG3M ), or make various mechanical checks.

X-Z Tram; Y-Z Tram;
Thrust Bearing Test using a .0001" test indicator and a 5/16" ball bearing on the end of the X and then the Y ball-screws.
Looking and the Ballnut Pre-load or loss thereof of the X and then Y ball-screws.

Your control also has bi-directional laser compensation and possibly backlash compensation active which was set up when new and in good mechanical condition.

Greg W