Hi,
I use 0.4mm and 0.5mm (16 thou and 20 thou) endmills for making PCBs. I use a touch plate, actually the copper plated PCB
blank. I have had success with this method, ie not breaking the endmill, with Mach3 and a parallel port and for the last two years Mach4
and an Ethernet SmoothStepper.
May I suggest setting up your touch plate but install some sacrificial bit of stiff wire or similar and experiment. Once you get it sorted and
realize just how good probing really is you will NEVER go back to doing without it!
Craig