1991 Monarch VMC 75 with Fanuc 15M control.

With the counterbalance adjusted to spec the control faults out with any rapid Z movement in either direction. The tech's went through the machine and adjusted the gibs, checked the backlash, and the lock nuts on each end of the screw. The backlash was .002 and after torquing the lock nuts to spec there was less than .001 vertical movement on the screw. I had them remove the fail safe and get the torch readings on the screw in both directions with the counterbalance set to specs and their readings are well within specs. The operator had turned the counterbalance down to put more weight on the head so the control wouldn't fault out with "pulsecoder disconnect" error. My guess is they don't have the backlash comp setup correct but I didn't look at the control yet. It seems the scale and encoder are fighting each other and by putting a lot of weight on the head it has more weight on the ball screw. Even with the counterbalance turned down the control faults out when performing a fast peck drill.