Terry, I think you'll be OK. The Tormach has 5tpi leadscrews, thus .200" per revolution. The stepper motors are 200 full steps per revolution, with a 4-step cycle of ++, +-, --, and -+ of current in the stepper coils. The drivers are microstepped at 10 microsteps per physical motor step to give .0001" per microstep.
Stepper drivers, when they are powered up, come up in a hardwired configuration of phases being energized, but always on a specific full step of the four-step cycle. In my experience, this may vary from controller to controller, but at most you'll be two full steps off where you left off (which was more than likely on a microstep and thus partway between full steps).
So, if my understanding of stepper motor driving is as good as I think it is you'll be at the most +/- .002" from where you think you are. 1/4-20 you'll more than likely be OK. Finer threads, YMMV...