The post processor I have been looking at uses g31 z -100 to drop the torch until the probe switch changes state, g92 z0.0 to zero, then g00 z25.00 to raise it by the preset distance, g92 z0.0 to zero the z axis and g00 z1.00 to preset the pierce height.

this is from sheetcam, will that not work in mach3??

i need to ref home one axis at a time as all my limits switches share one input pin, that's fine and works well.