Stepper controller to manually input a specific degree

[Jonathan]

How are you coupling the stepper motor to the spindle? If it's just with a belt then forget it. The torsional stiffness of even an unreasonably large stepper motor, combined with the stiffness of the belt means you'd probably be able to cut foam with it but not much else.

You need something like a worm drive or harmonic drive. Worm drives are good here since although they have a bit of backlash, this can be minimal and they generally don't backdrive. You can make one easily by attaching a stepper motor to a rotary table. This post shows one I made recently. It's just two simple parts you can easily make if you've got a lathe. Or you could buy one from Arc Euro.