[Tytus Gerrish]

well if its losing zero gradually while cutting it.
is probably the stepper motor losing count. that's caused by tolerance in the drive mechanism and backlash transmitted through the cutting tool. sharp well maintained tools designed for the material you are cutting are a must for such machines. my best suggestion to fix the inaccuracy it accumulates without too much work is to adjust and tighten all bearings, lead screws and nuts. put some clamping pressure on the machines tracks to take out some of the machine play and vibration. and make shure the whole system is well lubricated. also low quality terminations on the power wires and frays in the motor wires can cause intermittent loss of motor power and therefore loss of zero. i am cuttently in the process of converting my stepper motor 3-axis mill to ball screws because of these problems .also if you are having troubble losing count you can try adjusting the amperage to the motors. increasing it will make them hold position better, and you can also try changing between full step 1/4 1/8 and 1/2 steps if your board has that capability. single step has the most electromangets on at the same time for best holding and the fraction steps have higher resolution but less electromagnets activated simultaneously so less holding force