Hi have built a 8x4 router/plasma table, most things going well but would like to add touch off height setting, sounds like the controller won't do the gcode G28.1 G90
has anyone got one going on plasma, every thing else is working well,
Have you tried using G31 for probing? It would probably be something like "G31 Z-10." which would send the Z in the negative direction for 10 units and it will stop whenever the probe input is activated. After that you'll need a "G92 Z0." if using something like an ohmic sensor or "G92 Z-.5" if you were using a floating torch that traveled .5 before activating the probe.
got round the problem by purchasing a THC unit works great but modify the Z axis for plasma as I thought someone was going to purchase the machine,
so building an other table slightly bigger, with plasma / router in mind again, just made modify a china spindle for ATC works great,