Being a newbie, I don't quite understand how the machine knows where it is. Depending on which threaded rod used, different pitch = different speeds correct? The unit I plan on building calls for 1/2 - 10 Threaded rod, I want to use 1/2 - 10 Acme rod. I know that they are about the same, but I still would like to understand how it would work. Can some one educate me on this.

Thanks

You tell the control software how many steps it needs to send to move the machine one inch. this usually equals 200 steps per rev(stepper) times number of turns per inch (leadscrews) times microstepping amount (8 for 1/8, 10 for 1/10...)