We have a Cincinnati machining centre with CNC Pro fitted, about 6 years ago. We have had a few issues with Z heights, but I had though we had overcome/worked round them.
Recently we have a new operator who has had a few crashes since joining us. I though it was him, until I took over, made a program which faced the top of a plate, going first to Z-0.75 mm, traversing in X, then to Z-1.5 mm before returning in X to original position. The first item I machined was fine. I put a second plate in the vice and pressed start, it machined the first cut, but then, instead of going to Z-1.5, it continued down, until the spindle head hit the plate. A distance of 150 mm, or more.
Does anyone have a clue as to how this could be? Surely if the distance traveled, does not equal the command there will be a fault and it should stop? I checked the encoder output on a scope and it is normal, just the same as the X & Y axis. Could some new interference noise be an issue, but again I would have thought that once it was going where it should not, it would fault? Could it have switched between absolute and relative distance to travel?

All help and pointers will be very gratefully received, as we can no longer trust the machine to go where commanded.

Regards, Colin