[craynerd]

Hi guys, I have an electronic divider and want to hook it up to my lathe spindle so I can set work in the headstock and use the lathe spindle for divisions with a milling or wheel cutting attachement setup in the crossslide.

My intention is to use a setup similar to the attached picture. This is NOT my picture but will be exactly the sort of setup I am looking at.Attachment 395244

This uses a 10:1 timing belt but with 400 steps per rev on the stepper motor, that’s only 4000 steps per revolution and an accuracy of 360/4000 = 0.09 deg per step. Now that seems pretty damn good to me but I currently have the same divider attached to a rotary table with a 90:1 worm wheel reduction, giving: 400 steps x 90 = 36000 steps per rev. So 360/36000 = 0.01 deg per step!

I know for a fact this setup works really really well and is super accurate for my clockmaking. So I have been advised to use a geared stepper motor along with a timing belt. Although I have experience hooking up stepper drivers to motors and can do this, Ive no experience with these geared motors. Is there anything I need to consider and does anyone have any recommendations (ideally uk supplier) for a suitable geared stepper and drive belt combo? Does anyone have any thoughts on needing the 90:1 higher resolution or will the 10:1 resolution be acceptable?

Any opinions, thoughts or sources of geared steppers would be appreciated!

Chris

[ger21]

I would think that a geared stepper would have too much backlash.

I'd look for a planetary gearbox, which would have lower backlash.

https://www.automationtechnologiesin...ation-systems/

Or even better, a harmonic drive. But I'm not sure you can find one that bolts to a stepper, and they can be quite expensive.

[skrubol]

I'd be more concerned about torque than the resolution. Do you have a particular stepper in mind? You mentioned .9 deg. steps, which is not the norm (1.8 is.) If the stepper you use is really a .9 degree step motor, your resolution is actually at least half (.45 deg) if you've got at least a half-step driver. Normally you can get a bit better than that if you aren't running the motor at full torque.
10:1 is very high ratio for a single timing belt though. Do you have room for the larger pulley? What tooth profile pulley are you planning on using (it matters for things like this.. Don't use MXL/XL etc.)

[dixdance]

I would think that a geared stepper would have too much backlash.

I'd look for a planetary gearbox, which would have lower backlash.

https://www.automationtechnologiesin...ation-systems/

Or even better, a harmonic drive. But I'm not sure you can find one that bolts to a stepper, and they can be quite expensive.

There are lots of used harmonic drives on ebay

If the harmonic drive doesn't bolt directly to the stepper, could one use a timing belt, and get even more reduction without any backlash?

[ger21]

Yes, but be sure to use a timing belt like an HTG or GT2, which have lower backlash. You can also buy pulleys with lower backlash than standard from places like Brecoflex.

It might be easier to just buy a coupler to connect the two together if they have different shafts. Harmonic drives tend to have high reduction ratios, so you shouldn't need a belt to provide additional reduction.

[kawazuki]

There are lots of used harmonic drives on ebay

If the harmonic drive doesn't bolt directly to the stepper, could one use a timing belt, and get even more reduction without any backlash?

Timing belts whilst not brilliant are a pretty low cost / low backlash solution ....... the OP is using a worm driven rotary table that are renowned for lash! If you wanted better resolution then just add another 10:1 reduction but it'll double the single stage reduction backlash! Torque isn't an issue as this isn't likely to be 'high speed' machining - with a 10 x 10 reduction it would be a 100 fold torque increase.

[Bdrangdo]

I'd be more concerned about torque than the resolution. Do you have a particular stepper in mind? You mentioned .9 deg. steps, which is not the norm (1.8 is.) If the stepper you use is really a .9 degree step motor, your resolution is actually at least half (.45 deg) if you've got at least a half-step driver. Normally you can get a bit better than that if you aren't running the motor at full torque.
10:1 is very high ratio for a single timing belt though. Do you have room for the larger pulley? What tooth profile pulley are you planning on using (it matters for things like this.. Don't use MXL/XL etc.)

I believe that 5 phase steppers are actually .9 degree.