Need help understanding rotary attachment configuration

I purchased an OemTech K40+ machine a year ago, and it came with a roller attachment and Lightburn included. Recently I decided to use the rotary, but I am having many issues with it to the point I am even thinking this attachment is defective.

The physical installation is done, but the Lightburn settings are confusing

To start, the mm per rotation is not clear. Lightburn says it is the circumference of the rollers. The diameter of the roller is 25 mm and the circumference is 78.54 mm. Why is Lightburn asking for it when it can be calculated with the diameter?

Also, once I entered the diameter of the object (60.7 mm) and hit “TEST”, the roller rotates the object almost one full rotation. Why not a full rotation if I entered what Lightburn asked for? After adjusting the mm per rotation (from 78.54 to 83), it does a complete rotation.

Here is what is even more confusing:

If the TEST is working fine, I would guess the settings are correct and I can go ahead and start engraving, or that is what I thought…wrong

If the object’s circumference is 190.695 (based on its diameter), I would understand I could be able to engrave a thin square with a length of 190.695 mm and cover the whole circumference of the object, however, when I frame the movement of the laser and the rotary, it covers twice the circumference of the object, meaning the square would completely overlap. What am I missing here?

I went and changed the mm per rotation to 41.5 so the framing shows one full rotation. Why does this value need to be adjusted if the roller diameter and the mm per rotation should never be adjusted? or that is what I thought.

Once more, by changing the mm per rotation messed up the TEST part in the rotary setup because it now rotates the object half. It needs 83.

Also, if this is a common issue setting up this attachment for every object with different diameter?

I decided to engrave a 40x40 graphic and the result is disastrous. The graphic is completely distorted and deformed.

I am using “Current Position” instead of “Absolute Position” and is it normal for the object practically rotates briskly before starting to engrave and once finished, rotates the object a few times really fast before stopping? Is there a way to tell Lightburn to start engraving right on the current location and stop and remain in the position where it finished engraving?

If you have a roller rotary, there is no need for an object diameter … you only need this with a chuck type rotary.

When you click on the test button, the roller should rotate one complete rotation and back…

Since a roller drives the surface of the object, not the center, there is no need for an object diameter.

Make sense?


@jkwilborn is correct.

Here is more information that might be helpful.

Thanks for your responses, but I am still not sure why I cannot make my rotary attachment work properly.

I understand why the object diameter is not required for the setup, however, the diameter and therefore the circumference are needed to know the maximum area available for engraving, correct?

If I have a bottle with 2.4” in diameter (circumference of 7.5”), I assume I can create a drawing 7.5” long and fit perfectly around the bottle ‘s surface, but I can’t. The drawing is stretched so long that is overlaps a lot as if the drawing were around 12” or 14” long.
Why is it doing that?

Do I need to go every time to the rotary setup and change the “mm per rotation until the “Frame” tool show the proper rotation? Or just reduce my drawing ‘s height accordingly?

Post a screenshot of your rotary setup screen please.

It would benefit all of us if you would answer the questions put to you. You have added nothing to help us assist you with this issue.

Unless you respond to the queries, we can’t help you.

Good luck


I don’t see any questions asked? Unless I’m missing something.

I know how I got my roller rotary to work but the community doesn’t agree with my settings.

Here are some troubleshooting I found from

a. In LightBurn, create a rectangle that is 80mm wide x 5mm high.
b. Rotate the design 90-degrees so that the 80mm dimension runs along the round part of the cup.
c. Engrave the design.
d. Measure the rectangle in mm. (For this example, lets say it measured 95mm.)
e. Divide the measurement by 80. (e.g., 95 / 80 = 1.1875)
f. Find your current steps per rotation. (For this example, lets say it is 5000.)
g. Divide your current steps per rotation by the value obtained in step e. (e.g., 5000 / 1.1875 = 4210.53)
h. Test the value calculated in step g as your steps per rotation.

Here it is a screen shot of my rotary settings

When I hit TEST, the object does a full rotation and it returns to the initial position, which it is what it shoul do, right?
But, when I frame the 155 mm thin square you see next to the rotary setup, it does 2 full rotations.

Lightburn needs to know the diameter of the roller. I assume you have that correct. Is that diameter marked on the rotary or in the docs, or did you measure it?

The mm per rotation is not directly related to the diameter of the roller, it is related to what your controller setting is for your Y axis. You need to experiment with that setting until you get the correct setting, then you should never need to change it again. Since you said it’s making 2 full rotations at 84, change it to 42.

Lets work with easier numbers. Make a 100mm skinny box, cover your tumbler or whatever you are working with in painters tape and set your layer to a low power burn, just enough to mark the tape. Run the test and remove the tape and place on a flat surface so you can measure it. If it now measures 100mm, you’re good. It will probably be off by a little bit at this point. If the test burn is less than 100, increase your mm per rotation and repeat the test. If larger, reduce. It is trial and error until you get it perfect.


I did what you mentioned and it works, but that is what I wanted to avoid: making calculations everytime I wanted to engrave objects with diferent diameter. I thougth it was only matter of measuring the diameter of the object and adjust my drawings based on the maximum area available on that object.
I guess I will have to get used to that now.

Thanks all for your help :slight_smile:

If you now have a correct setting for the rotary, you do not need to calculate anything. Those settings will not change. You only need to know your object diameter for your design. You don’t need to change the rotary settings.

Since it’s a roller it is using distance covered by the roller, if it were a chuck rotary you would have to calculate the object diameter every time.


I guess as long as I use objects with the same diameter, I will not beed to modify anything, but when I use objects with different diameter I will have to adjust the mm per rotation,correct?

I mention this because when I use a different object, the TEST function does not make a full rotation

No, because it is traveling along the outer circumference of the object. It knows that when the roller travels 1 rotation it covers x distance. It doesn’t matter if your object is 1" or 5" diameter.

Forget the test button. Use what works. Try it on something of a different diameter using the tape. You should see the same results.

You might need to adjust your designs SLIGHTLY to get a perfect full wrap, if that 's what you’re going for. It’s easy to stretch or squeeze a little bit if needed. But don’t keep changing the settings once you have them dialed in.


Thank you Thelmuth,

I finally understand now.