Somewhat confused on the z axis homing setup for a plasma gantry.  Currently I have the z axis homing at the top (max torch to table height).  I plan to use a THC-300 unit with the torch.  I am aware that I need a spring loaded switch to define top of material.  Does this switch become the z home signal or can I still use the home signal at the top and input the material top through another input in mach ?  I have noticed that with my current setup, whenever sheetcam puts in z movements, the motor wants to drive farther up past home and sheetcam won't allow a negative value to be input for the torch height.

Thanks guys.

I  just installed a THC 300 on my plasma table and went through the same confusion. I have a spring loaded floating head and the switch that is triggered by that, indicating material top is mapped to Z home. When using SheetCam with the THC300 post processor the Z Axis moves to the location homes to material top and then lifts up to the pierce height setting in the setup. I hope that helps out.