I'm not sure if this is in the right category. I have a park Industries CNC Profiler. We are using it to profile Indiana limestone. We have had a problem for the past 6 weeks where the Z axis will drop for no reason. The machine can be in a cut or it could be hanging in the air. The drop is totally random. When I say drop, it will drop about 1/4" and go into feed hold. The error message that we are getting is an excessive following error on the Z axis. We have eliminated anything mechanical: new feed screw, rebuilt axis motor, new slide bearings, ect. The machine has a NUM Controler. The axis amplifiers are MTS Automation (X&Y are AC07's and the Z axis is an AC10). We have also replaced the AC10 amplifier with a known good one. We cant figure out why the Z axis will drop. If anyone can help I would be greatly appreciated.