# Rotary formula question

Ihave been working with lightburn and the rotary chuck tool, but I cant seem to figure out a formula for the Rotation. To get a perfect circle I am starting at 50 and working my way up. Does anyone know how to calculate the rotation based on diameter?

You or it doesnâ€™t need to know thatâ€¦ If your steps/rotation (mm/rotation) are correct the software will compute surface speedâ€¦

Assuming a chuck type rotary, a wheel rotary doesnâ€™t require any object diameterâ€¦

Try this thread and see if it helps you outâ€¦ Iâ€™m not a wizard with theseâ€¦

Good luck

Hello, Bobby
What setting are you referring to 50 and up?
To set up your chuck you need to know what your microstep driver is set to, usually 6400, 12800, something like that. Have to read the dip switches and compare to the table on the back of the driver. Then that number goes into the rotary setup steps per revolution. Then the â€śTestâ€ť button should spin the chuck 360 deg one direction, then back.
If you donâ€™t want to open up your case you can experiment, try different common microsteps until test gives you 360 degrees
Here is a photo of a common microstep driver table. Unless you have a gear reduction (Or belt reduction) it should be one of these numbers in the Pulse/Rev table. If new laser I would try 5000, 6400, 12800 first.

I think @Cyclops0 is using a grbl machine, so he doesnâ€™t have these types of drivers.

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Yes, for some reason I thought all chucks were steps per rev, not mm/ rev, learned something new today. Gantry thing I guess!

I think itâ€™s a controller thingâ€¦ mm/rotation is common with grbl

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When using the chuck multiply the Height setting (which is actually the width of the circle) by 1.25. Make that your new Height Setting and run your project. the circle should come out corrected. I am using an Xtool 20 watt with an RA 2 Rotary and chuck. Also, I am using Lightburn.

Sounds like a fix for an incorrect setting. but if it worksâ€¦

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