# Rotary math? Completely confused

I have the Atomstack X7 Pro and the Atomstack rotary.
Rollers are 16mm.
Object is 57mm in diameter.

How in the name of all things holy do I figure out the mm/rotation?
I can see that it has a circumference of 179.071mm, but that doesn’t help me.

What number do I put in for mm/rotation? Rotation of what? The rollers, the object, etc? It’s poorly worded and very counterintuitive. I’ve tried 16, 57 and 179. None of these values seem to work properly.

I can’t help with your particular roller rotary as I have the chuck style. However if you haven’t, this is worth a read

The mm per rotation value is correct when clicking the ‘Test’ button causes your roller - not an object on the roller - to make one complete rotation before returning.

Okay, so if it’s a 16mm diameter roller, should that value be 201? Pi x 8 squared?
If that’s the case why wouldn’t Lightburn do the math and fill it in?
I feel like I’m missing something here.

You don’t need to worry about the roller’s circumference - just enter the roller diameter, 16 mm.

Make sure you have Roller selected for Rotary Type:

There is a calculator in the Rotary Setup window where you can input object diameter and LightBurn will calculate the object’s circumference (or vice versa) but these values do not affect rotation for roller-type rotaries.

I read that, but I’m not sure what it means by dedicated rotary axis. I’m going to guess it means 360 degrees. But it could also mean Pi x radius of the roller squared. Or it could mean something like steps per mm. It’s very confusing and poorly explained in Lightburn.

Okay, great. I put in the Roller diameter as 16mm. I put in the object diameter as 57. (Which only figures out the the circumference, it doesn’t affect anything.) So what do I put for mm/rotation???

360 and 16 don’t work. Not even close. What is the mm/rotation I need to figure out?

I do not know the correct value for your machine and rotary - that’s what the test button is for.

Try out different values until you settle on a value that causes your rotary to make one complete revolution when you click the ‘Test’ button.

Your other options are contacting Atomstack and asking them directly, or searching around for a setup guide. A quick google turned up several YouTube videos that may provide the correct value, and other helpful instructions.

If the diameter of the object doesn’t matter, why is it even there? What’s the point of any of the values if putting in the value of the rollers is a, “I dunno, start guessing?”

What you’ve basically said is, “Take a guess at the right value for roller diameter. It doesn’t mean anything. Diameter of the object doesn’t matter. I really don’t know, blame Atomstack. None of these numbers mean anything, just guess and test.”

It is sometimes helpful to be able to calculate an object’s circumference and use that value to position graphics appropriately in LightBurn for how you’ll want them to output on your object. That’s why that calculator is there.

I am not blaming Atomstack for anything. I’m telling you they may be able to provide you with the correct value if you’d rather not go through the process of dialing in on it yourself.

With the broad range of hardware LightBurn supports, it’s not possible for us to know every mm per rotation value for each machine and rotary combination.

So what does the mm/rotation mean? You said it’s how many mm for the rollers to make one rotation. If the roller is 16mm, what am I not getting?

You’re just making it up as you go.

MM per rotation is the amount of distance you need to command your rotary to move for it to make one complete rotation. I’m trying to help, and I can assure you I’m not making this stuff up as I go. Please try to view my intentions here a little more charitably.

Yeah, my wife just figured it out in about 10 seconds.

It’s Pi x Diameter of the roller. Which the software should figure out for you. So for a 16mm roller the value is 50.27.

Poorly labeled, poorly explained, poorly implemented.
And “how long it takes to make one rotation” isn’t helpful.
Okay, I’ve given you values for the roller and the piece.
This is the part where you, as a support person, say,
“Oh, it’s Pi x D. May not be exact, but that’s a good starting point.”

That advice is not accurate for all machines and rotaries, but I’m glad you were able to find the value you needed!

1 Like

Check out this video

Once you get your head around it - it works. Just make sure you orient the the axis of your rotary apparatus correct. First time I did it, everything was backwards ??? Then flipped it around 180 degrees, and it was all fine. WE etched some wine bottles and glasses.

Pat

I’ve got the mm/revolutions correct now. For anyone else looking at this it’s the diameter of your roller x the gear ratio of your rotary unit. If you’re using an atomstack rotary, try 50 as as good starting point.

Still not sure what setting is causing it to etch flipped on the Y axis. X is fine. I just mirror it and it works okay.

Now to solve why it’s slowly moving up the roller as it works.

Next time someone asks, it’s roller diameter x gear ratio. Don’t just make up answers. Don’t start making excuses about why you don’t know. Tell them to ask the rotary manufacturer for the gear ratio.

I watched a dozen videos before some random person posted the correct answer, and you’re supposedly a support person. If you don’t know, don’t waste people’s time.

That made a lot of sense and helped me figure it out. Thanks!

I was reading this thread with interest. Strangely enough, my rotary dialog is different. The setting you are referring to on my dialog is steps per rotation. In trying to understand why yours was different, and reading documentation etc, it seems that the differences in how various lasers handle rotary causes this inconsistency. In my case, the steps per rotation value was never provided by the manufacturer, and there was definitely trial and error trying to dial it in. In my case the value was 8000.

The test button tries to rotate the roller exactly one rotation. The goal is to get the value in that entry field dialed in, such that the roller does rotate exactly one rotation. Evidently it appears that not all vendors treat rotaries the same, and I guess there is some trial and error. It’s great that for your particular rotary you have dialed it in.

What is very important here is what I have watched on countless YouTube videos, where I believe the authors are “doing it wrong”. I have seen many videos where the author states to place artwork on an object on the rotary, they adjust the diameter of the roller.

Here’s what I believe is not perhaps understood, and why the roller diameter and the other parameter are important. When Lightburn deals with art on the workspace, it deals in linear distance, either inches or millimeters. Knowing the roller diameter, as you’ve mentioned, Lightburn can calculate the circumference , which is a liner distance associated with one revolution. Let’s say for convenience that my roller circumference is 50 mm. On my laser, LB knows it has to pulse the stepper 8000 times to move the roller 50 mm. Or put another way, LB needs to pulse the stepper 8000 times to drawn an object that is 50 mm in that dimension. As I understand it, on GRBL machines, LB has to tell the unit to rotate a certain amount of degrees, instead of # of pulses. But, basically same is true, LB would know to tell the laser/rotary to rotate 360 degrees to move the roller 50mm.

This is where I’m finally getting to what I believe others have done wrong. Just as when you are engraving on regular flat surface, you adjust the size of the artwork to fit you intended engrave area. You do NOT adjust stepper motor settings to change the scale of the artwork. The same is true when engraving with a rotary, is you adjust the size of the artwork on the workspace, to match the size required on the object on the rotary. Many YT channels I’ve watched suggest changing the roller diameter.

I believe the “useful calculator” in the rotary dialog is there to help you figure out the circumference of the object you’re going to place on the rotary, because it’s easier many times to measure the diameter with a ruler, than to measure the circumference. Ultimately, as with regular engraving (flat surface) you want to know the size needed to engrave where you want on the object. I hope this is helpful

Ray