I have a garage built RF45 mill. I have a 2830 oz/in Nema42 on the z-axis. I bought such a big motor years ago because I didn't want to be undersized. I have found that I have severe resonance at 50 ipm that causes the axis to stall out. However anything below that number is fine, and anything above that number is fine (I have tried up to 135ipm).
Tonight I swapped one of my 960oz/in Nema 34 motors on to the axis and it ran it fine, and the resonance "sweet spot" moved up to 70 ipm, I'm guessing due to the differing torque curves. I think a 640 oz/in motor would run the axis fine as well.
My plan was to change the axis from direct drive to belt drive and keep the Nema 42. Then do a pulley setup that is 1:3 so that the actual speed of the axis at the resonance sweet spot would be 150 ipm and I can set my max speed below that and never worry about it.
The only downside I could think of would be loss of resolution, so I'm hoping someone can confirm my math..
Stepper motor is 1.8 degrees / step. I'm 10u micro stepping (Gecko g201) so that should be 0.18 degrees per micro step. Then multiply that by 3 for the gear increase and the ballscrew would be experiencing 0.54 degrees per micro step. 360 degrees / 0.54 would mean that it would take 667 micro steps per revolution. If the lead screw has a pitch of 5mm (0.197") that would mean that each micro step would be 0.197" / 667 = 0.0002".
If that's all correct, 0.0002" hypothetical resolution would be more than fine by me. Did I calculate anything incorrectly? Am I overlooking anything?