Variable power during a cut - Is it possible?

Hi everyone!
So I’m going to try to be clear and concise, but please tell me if I’m not!

What I’m doing is that I am cutting some parts of a spiral. So ideally the laser should follow the spiral and turn on and off depending on whether it should cut or not, instead of “trying” to find the best path to optimize cutting time.

This is a very long spiral with a lot of “turning on and offs” involved. So the fact that the laser keeps trying to find the closest cut instead of following the spiral is a big problem because it makes the job very long.

I can produce a svg file where the parts that have to be cut are of a different color to the ones that the laser should simply follow without cutting. But then, is there a way with lightburn to do what I want from there?

This wouldn’t be too much of a problem if it was a one-time job, but I have to do this many times, possibly hundreds of times, so any help would be very much appreciated!!

Thanks in advance,



Please post a picture of how the result should look along with what you have designed in LightBurn to process this job. Having a bit of a challenge “seeing” what you are trying to do.

If you are creating a cut that is a continuous spiral, the laser should run continuously. If you are engraving a spiral with thickness to the shape, you are engraving, not cutting.

If this is correct, consider to edit your post to reflect this aspect.

Ok Sorry, so I think I was not as clear and concise as I thought!

Here’s a simple example of what I’m trying to do. I’m cutting through a black, backlit material. Where the material is cut, the light can pass through. I do not want to engrave, just cut where the light should go through.

On the Morgan Freeman example below, I’m constructing a single, simple spiral. Parts of this spiral are white, the rest is black. By controlling where it’s black and where’s it’s white, the result gives the impression of a picture.

Now, What I’m trying to do, is to have the laser follow that spiral all the way, but only fire up when the spiral is white. Because right now, i’m only exporting the white parts and the laser is trying to guess the best path to engrave everything, and is making a bad job at it. This may not seem like a bit problem. But this is a very simplistic example. On more useful examples, where I have multiple, more intricate spirals, the path taken by the laser is extremely complicated and long, while it could only be a few spirals followed at a constant speed. Is there a way to achieve this?

I’m really hope this is clearer this time ! :slight_smile:


I understand what you are saying much clearer now, so thank you for that. The picture really helps. :slight_smile:

The laser is not trying to guess, it is doing what it has been told. While I understand you are trying to better optimize the processing of this work, the suggestion is not the best, “follow that spiral”, as the laser would still be traveling a significant distance with the laser off and that is not what we are after.

My guess is you may not have fully maximized the optimization options built into the LightBurn Cut Planner. I think your goal is to calculate and optimize for the least travel possible, to accomplish the task. This is where the ‘Optimize Cut Path’ and ‘Optimization Settings’, found in the ‘Laser’ window, are used to dial in the cut order processing.

This video was done back in 2018, we have added options, and the basics still apply:

Unfortunately there’s no simple way to do what you’re asking. We don’t have a way to directly control the output power based on the color of an input shape. What you’re trying to do here is a pretty unique case, and LightBurn is not designed to do this.

Ish… :slight_smile:

I guess I’m confused why you want to follow the spiral - the total distance you have to cut is the same, no matter what shape the path is.

The machine needs to be at the right speed at the right place in time to start cutting and throughout the cutting motion.

By using the ‘reduce travel moves’ and ‘choose best direction’ optimisation settings, you will get the shortest-travelled path for the object.

What am I missing?

So you’re engraving, but you want to line cut?

Or is it that you want to create a cutting path from a combination of spiral and image and that’s the problem you are having?

@Bonjour brings up an interesting issue I may still misunderstand. Is this work vector art or a bitmap you are working from?

I should have said cutting, in the “cutting mode” sense. This is confusing because I’m engraving in the sense that I’m only going through the paint on a transparent material, not cutting through the whole thing. However, this is done in cut mode along a vector path.

Ooops I can’t speak English apparently!

Yes, shortest, not quickest, on my laser. I think the problem is that LightBurn was trying to solve the “traveling salesman problem”, hence finding the shortest traveled path like you’re saying, but without taking into account the acceleration times, which made the resulting cut longer than if I was simply cutting the whole spiral. This was becoming a problem on applications that had several, more intricate spirals with different centers.
Thank you very much for your answer because I have watched the video and I think the “reduce direction changes” option is going to help me a lot to mitigate this. I will try it next time!

Thanks again for your answer and for trying to understand me!


Yes it is a vector art. I’m engraving it in the sense that I’m going through the pain layer of a transparent material. But it is done in “cut” mode. I understang this was confusing, sorry!

Is it possible to use ‘Fill’ at a faster speed to ablate the paint instead of cutting the paint layer with ‘Line’? I assume you need to weed out the cut paint shapes, is that true? With the correct (for your system) focus and Interval setting, you can produce very crisp shapes using the Fill as your cutter.

I noted you have a powerful laser - is it a flat-bed machine, where the gantry contains the tube, optics, etc as well as the focus head?

I have had a lot of experience with such machines and acceleration/deceleration is something you have to live with for the convenience of a large work area.

An example: the customer cuts whole sheets of material - MDF and ply, mostly - 2400 x 1200mm. They had a job that was intricate and no matter what tuning I did, the job came out costing too much.

The solution was to get a smaller machine (1000 x 1200) with a lightweight head that, even when factoring in the time to swap media and restart the job, ended up 1/3 of the cost of the bigger machine. It was all about the mass of the gantry.

They ended up outsourcing it and still made money :slight_smile:

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