Weird issue with z axis non-symmetrical movement

[Xnaron]

Hi,

I have a plasma cutter and I added a z axis to it. I command the axis to move up or down 1" with the axis set to zero. When I lower the axis 1" (G0 Z-1) it moves 1.035" measured by calipers. If I move the axis up 1" it moves 1". I have ruled out backlash on the ballscrew as I have swapped two wires on the stepper coils to get it going in the opposite direction and it does the opposite. It moves 1.035" when I raise it 1" and 1" when I lower it 1". For my tests I eliminated backlash by jogging up and setting zero and moving up 1" to test. I did the opposite to test it lowering. I am at a loss as to why this is happening. Maybe I am missing an offset somewhere? Any insight appreciated.

Thanks,
Brendin

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[Xnaron]

Turns out this is being caused by the Proma THC SD. When I take it out of the equation the movement is correct.