Why is GRBL controller taking y-axis into account when using a Chuck rotary?

So I built a chuck style rotary. Basics are:

1.8 degree stepper, 5.18 to 1 gear ratio, 128 Micro steps (honestly not 100% sure but the math is close?)

So using lightburns suggested formula we get:
(200 * 128 * 5.18)/360 = 368.35 steps per 1 degree rotation.

This does not turn far enough. In fact using a 6 inch long “arm” and testing the right answer is 415.69 steps per 1 degree (the number input into the Steps/mm section).

Baffled I was messing with the controller settings and changed the y-axis steps/mm from 40 to 80 and the rotary did 2 full rotations (with 415.69)… what? I was under the assumption that this number was ignored or replaced while rotary was enabled.

So I guess im asking if anyone can shed light on this for me as to why lightburn is using this setting, or how it fits into the equation?

And as a note I tried this in a different machine with a ruida controller, calculated the steps for a full rotation as 16576 and it worked flawlessly.

It’s a machine that moves the rotary just like it was the Y axis, since it is moving the Y axis. The rotary ‘rolls’ back and forth as the table would travel back and forth in the Y direction.

Check this Rotary Setup and see if that helps.

Good luck :slight_smile:

P.S. ensure you save your original configuration so you can restore it when you remove the rotary device. Don’t forget to save the rotary devices configuration also.

Bah! Ok easy once I messed around for hours… maybe I just cant understand the way it was written in the “rotary setup” page but here is the solution that makes sense to me:

Motor steps per rotation * gear ratio * Micro steps / steps per mm = mm per rotation
200 * 5.18 * 8 / 40 = 207.2

If only I was better at math, I would have figured this out hours ago!

What controller are you using? Also, how did you come up with your 5.18?

May be this helps:
https://www.youtube.com/watch?v=UOWXlBaYxS0&t=20s