[CNCAddict]

If you're using servos, putting the encoder on the ballscrew is a bad idea. This will result in a very low system stiffness or you'll get some nasty oscillations at a high stiffness. As for pulley sizing, I am using tiny little Nema23 servos with a 3:1 reduction and a 10mm lead 25mm diameter Hiwin ballscrew. Maximum axis thrust was calculated to something like 900lbs with a continuous thrust of over 300lbs. This will be going on a 12" lathe and I think these values are more than enough for what I will be doing. I'm only using 2mm GT-2 belts which are very small but have very low backlash. Belt loading is only 12lb at 300lb thrust so I don't think this will be a problem (although pushing it). Also remember that a well tensioned belt spreads stiffness across both sides of the belt, so the actual belt stretch at 12lb belt load is equal to 6lb per side. One side of the belt relaxes by "x" while the other side stretches by "x" so they share the load. Anyway, you can see below how far I've gotten. Should have it finished sometime next month