Mm per rotation confusion

LightBurn Software Questions
1

I’m trying to setup my first rotary burn and in the set up it asks for mm per rotation. I don’t understand this because for the last 30+ years of 4th axis work, it’s always been in degrees. I’m confused why lightburn needs this info since I’ve already given it a diameter. The mm per rotation will change with every new diameter on every workpiece but the number doesn’t change when I enter a new diameter.

Lets assume my workpiece is 1"…now lightburn knows that the circumference is pi…so do I just enter 79.7963 mm per rev??? Why doesn’t lightburn automatically know this when I enter the diameter?

Additionally, why does it need this? I’ve given it a diameter and it knows the size of the picture that will be “wrapped” around that diameter. I don’t even know if I’m asking the right questions.

I should mention that I’m using a 100mm chuck and cnc router is not connected to lightburn so I can’t use the “test” button. I don’t even know what it would be testing for.

Edit…hold the phone! I just realized that I had not selected the A axis…derp.

2

This is for a chuck rotary. A roller is different. On a GRBL machine it’s mm per rotation, on a DSP it steps per rotation. Either way, Lightburn needs this info to calibrate one complete rotation. Once this is set it never changes. You need to input the size of your object every time to get accurate results, but you don’t have to change the mm per rotation value. This might help your understanding.

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3

I just realized why had confusion, I didn’t select the A axis and now the mm per rev is greyed out. But Thank you for your reply. I don’t know what grbl or dsp means but I think I’m on the right track. I still don’t get the mm per rev thing but it looks like it doesn’t apply to me.