It is up to your system. some users have 3:1 or 5: 1 or 2:1
I am looking at putting a servo cnc mill together, I was reading an earlier post about need to use reducer gearing if I want the servos to run smooth at slow speeds. Does anyone know what slow and fast speeds that I can expect I don't use the reducers? Are there any other ways of doing this without the reducers?
Timing belts are used very often with steppers. Depending on the motors though. Belts will give you better torque out of smaller motors assuming the pitch of the screw isn't too high.
I don't often see that done with servo builds though.
My mill runs straight steppers on X and Y, but I had to put a belt on the Z to get satisfaction out of it.
Another reason guys use belts is that they are more forgiving with regard to motor screw alignment. I generally use ridgid couplers and if you get a motor mounted wrong with those in place, you will know quickly.
I guess it all depends on your hardware - linear bearings? Sliding ways?
I had a machine (now dismantled) that had linear bearings, 10 mm pitch ball screws and some good Nema23 brushless servos direct driving them - it worked very well, very fast, very accurate.
Ken, I think you need to modify your vocabulary and picture in mind ! Smooth and Slow don't cut it or define what you will ultimately wish for when the machine is up and running. If you run a 5 pitch ball screw and 4 to 1 drive ratio then you could expect to be in the range of .0002 or better resolution ! You could also expect to have rapids in the range of 80 to 140 in min. In a milling machine you don't need any faster rapids as it is shocking enough to crash into part at 80"min. With a resolution of .0002 you will be able to do some serious precision with some presentable finishes.
IH v-3 early model owner