There's a manual for the plasma configuration in your Docs folder of Mach. I attached it to this message.
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Plasma machine configuration is similar to that of a mill or a router. THC, however, is handled with an
out-of -band motor. For example, if Motor 2 in the profile is mapped to the Z axis, an out-of-band
motor must be enabled and its motor tuning settings must match those of Motor 2. If Motor 5 is used
as the OB motor and axis, it must be assigned as OB1(6)
In the Configure drop-down menu, open the Plasma Screen Configuration panel.
Default THC mode, THC Axis, and the Analog Register will be set here.
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In short, set motor5 to be matching your Z axis Counts per unit, accel, and velocity and map motor5 to OB1 for plasma. If you can't get normal motion out of your Z axis, then you will not be able to get THC motion out of your Z axis. You can start by testing Manual mode to see if you can get up and down commands by clicking. If you can do that, then we could move to Digital.
Do you have other motion controllers or do you just have the ESS?