I have been experiencing a Z height error on my machine. After about 30 minutes into a program machining a block of nylon, the Z would correctly raise up to 0.000 at the completion of a path, the gcode is calling for another 1/8 inch deeper cut, the DROs read correctly but the tool is 1/2 too high, cutting only air. Everything is very tight on the Z axis. It's a pinned lead screw drive and the axis is never under load at the time of the error. You can hear and see that the tool never touches the work. I can restart the program at the point of error and it continues correctly for some time and then the same Z axis error will occur, but I just keep re-zeroing the Z and restarting the program and completed the part. The error has always occured on the -Z instruction.
I mostly use the machine for Plasma cutting with a Bob Campbell THC controller and have never had this issue while plasma cutting. The THC was on at the time but the THC button in Mach3 was inactive. I'm running a 2 1/4 hp Hitachi Router Spindle.
I have not updated Mach3 for over a year. I'm at work right now, not sure what revision I'm running.
Does this sound like it could be a controller problem?
Thanks in advance for any help.