I am using a 6040 Cncest CNC cutting letters on a sign at 3mm deep when for no apparent reason the cutter plunges to 7mm deep could it be a software problem as I am using MACH3 and Vcarve10,5 running windows 7 with a parallel port.or maybe a stepper motor problem as it only happens with the Z axis and has happened a few times before. Any help would be appreciated.