The racks, pinions, and power supply arrived yesterday and I setup a trial run to verify the motors would have enough speed/torque with the selected gear ratio. First, I bored a few thousands out of the pinions to allow a press-fit onto the stepper shafts. Next I pressed the pinions onto the stepper shafts; luckily the steppers have a hole in the back of the case that allowed me to support the other end of the motor shaft so that no force went through the motor bearings. I then verified the pinion/shaft run-out with a dial indicator; all except one were well under a thousandth. I was able to bend the one with a few thousandths run-out to match the rest; there was no way to protect the motor bearings during this process though so hopefully I didn’t cause any longevity problems.
Once all the pinions were in place I cut the racks to final length and modified the Smoothieboard electronics and configuration files to accommodate a 2nd (and inverse rotation) motor on the X axis. I then wired it all up and began testing. It all seems to work great and I was getting what seems to be plenty to torque all the way up to 1200in/min. The rack also seemed to have very little backlash, even over a range of different engagement depths. I don’t have any good way to measure the torque, so I just pushed against the rack by hand with a force that I assume is far greater than the moving/cutting resistance. So it remains to be seen if 1200in/min will be the actual speed; I also verified there is even more torque at lower speed, so I can always slow it down if need-be. Speed will probably be limited more by the spindle/tooling/material anyways.