It's because you got the wrong model if you want the software to move the Z for THC, I have no idea how the SD lets the control software know its moved Z instead of the software. With no bidirectional communication to the software it operates as a quasi-stand alone THC but it still relies on the software to do things like touch -off , raise to rapid height , Torch on , etc. I gather your goal is to do this build on an absolute shoestring. The good thing is you are getting a free eduction about things that either won't work or will take a lot of time to get a marginal result.This doesn´t make much sense to me as the CNC board would be the Z-driver already ?