DIY CNC Kit: RF45 Milling Machine CNC Conversion / Retrofit CNCCookbook
The IH reduction is 4:1 via pulleys and another 5:1 via the ballscrew, or 20:1. Tormach says their rapids speed is 65 ipm. Let's plug these numbers backwards and see what we get: 65 inches / ″ = 650,000 ten thouhs = 650,000 steps per minute. 650,000 steps per minute / 200 steps per revolution = 3250 rpm.