motor torque for a stepper....more of a size that anything. With rack and pinion the motor needs to be geared or belt reduced 3:1 to get back to the original motor torque because of the ratio in the pinion. Even fairly small diameter pinions are PI times the diameter. If you know the pitch of your rack and the pitch of the pinion (Teeth per inch) then the you can calculate the distance the pinion will move the load in one rev. Take a pinion with a 1" DP. It would move about 3.14 inches linearly in one rev. Hook up a stepper direct and spin it at 600 RPM and you have 1800 IPM speeds. Impressive but not very usable. Those kind of speeds throwing a mass about (even a moderate one) will be hard on anything lightly built. Build it heavy and the forces get worse.
Unlike a router, where depth into the cut is usually more critical, a good THC will compensate for vertical deviations. It can easly compensate for a rise of 1" over 6". You need to make sure the design takes into account the piercing process where the pierce needs to be made at a precise height above the material each time and for a variable delay based on feedback from the plasma rather than a preset pierce delay.  |