I do threading using a stepper (Nema23 2Nm) mounted on the spindle and control it as C-axis. This works fine and you can do any pitch threading. No need to have a box full of taps. For most jobs, 2 Nm is strong enough, can't even run it at max speed otherwise deflection of the part will be to much. And for the larger threads, just reduce speed and cutting depth. Takes i bit longer but who cares, it runs automatically. I recently changed to Nema24 4Nm because i had trouble threading ER32 (M40) on Cr42Mo4 steel. Works even better though i found out today the problems where caused by the power supply (now outputs only 14 Volts). If you have a stepper mounted on the spindle, you can do other cool things like broaching, knurling and grinding drills and end mills. It turns your lathe in a very versatile tool.