Rotary Configuration on A Axis Issues

Machine: K40 came with nano2 or what ever was in it.

Board: Laserboard

Firmware: Whatever it came with.

Problem/ Question: I am trying to configure my Rotary but no matter what I set the delta_steps_per_mm to it never moves the correct distance. If I tell it to move 10mm in lightburn and click the rotate button it moves about 1mm, if I say 50 it moves about 10mm.
I have used the documenation to calculate the steps per mm to put in the config and it comes to 8.8888.
My Gear on my Nema 17 is a GT2 Pulley 20 Teeth 5mm bore 6mm Width 20T and both the roller gears are the same. So (200 x 16 x 1) / 360 = 8.8888889.
The diameter of my rollers are 26mm which is set in Lighburn rotary setup.

What am I doing wrong?

If the belt drive is 1:1 you can ignore it completely in the calculations.

Your steps per mm need to take the diameter of the rollers into account.

Calculate the circumference of the rollers:
pi*26 ~= 81.6814076
1.8° steps at 16x microstepping is 3200 steps per revolution.
distance per step:
81.6814076/3200 ~= .025525439875 mm per step.
1/.025525439875 ~= 39.1766020447 steps per mm.

Enter 39.176 as your steps per mm value and see how that behaves.

Ok I will give that a try when I get back out to the shop. If the roller circumfernece is calculated here what do you put in Lightburn in the rotary setup where it asks for the roller diameter? Wont including it in both places make everything off?

I forget why lightburn needs it in addition to the controller, but there was a reason, it was explained to me once, and I promptly forgot.

Just did a test using that value of 39.176 and setup the strip test on a jar with blue tape. My circumference of the jar was 275mm. I ran the job and when it should have rotated one time it actually rotated four and a half full revolutions around the jar before it started to come back and do the other side of the strip.
39.176 is way to much, I was running 8.5 and it was close but not consistently accurate.

Apologies if I am behind on any particulars of your setup, Nick, I was out since last week with a bad cold.

Our rotary setup guide covers the “trial and error” process if your rotary manufacturer/ designer has not provided the correct steps per mm value for you to use. Before you even click any buttons in LightBurn, you must have the LaserBoard with the delta_steps_per_mm set correctly, so that when you send G0 A360 through the LightBurn Console, the roller rotary wheels turn 1 full rotation.

The LightBurn docs cover the specific details @loather loather is referring to, and yes it’s a difficult one to recall correctly (I may not have done so either!):

LightBurn only really needs 1 value, and that is to help you with the “Y stretch” of your design to fully wrap the round object being engraved.

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