Question about new digital stepper controllers

[Jonathan]

If you gear it down with a worm gear drive then far less torque is required from the stepper motor since (the majority of) worm drives do not drive backwards - if you apply a significant force to the worm-wheel the motor will not spin. Backlash might be a problem, although there are ways to reduce it to a negligible magnitude.

Also, since you only require 180° of movement, you could use some sort of lever arrangement with a ballscrew which can have very low backlash.

[irving2008]

If you gear it down with a worm gear drive then far less torque is required from the stepper motor since (the majority of) worm drives do not drive backwards - if you apply a significant force to the worm-wheel the motor will not spin. Backlash might be a problem, although there are ways to reduce it to a negligible magnitude.

Also, since you only require 180° of movement, you could use some sort of lever arrangement with a ballscrew which can have very low backlash.

Very true Jonathan, in a static situation where you are holding the work steady while cutting. If however you want a true 4th axis to rotate the workpiece while cutting you'll still need the same stepper torque to drive the worm chain. That said, a worm arrangement is probably better than using belts for this, although I have seen it done both ways. I modified a 4" rotary table to do the same thing. With a 9:1 worm reduction it gives 0.2 degree resolution and a 1Nm motor seems more than happy with the small workpieces I have used, e.g. gear hobbing on 50 - 60mm dia gears..

[Jonathan]

Very true Jonathan, in a static situation where you are holding the work steady while cutting.

Fair enough, I thought the plan was to just index the cutter.

I've also converted a rotary table - vertex HV6 which has a 90:1 worm drive and 1Nm stepper. It works well for timing pulleys pulleys, but there is a bit of backlash. A harmonic drive would be ideal, although rather expensive.

Also if you've got a lathe it's not difficult to make wormwheels, here's one I made a few years ago:



This was the process: