Contained Flames When cutting

Hello i am just showing some concern and confusion. The past week i have watched my forge cut and there have been flames only while cutting. Before it small and few people said it was common. Then the flame got to be close to an inch big and now im afraid to use it. I have cleaned the air assist fan and the fan in the back and cleaned it and attempted to cut last night and still flames. Can anyone help with advise.

Something that can happen when you are cutting really close to a hole in the material (or close to an open edge on a scrap), is that the additional air feeds under the material to the flame and makes it a little higher. Watch it while the machine is working, and if you see the flame being blown towards the front of the machine (horizontal) by the air assist, then it is likely nothing to worry about.

If you see the flame going straight up, or see the flame linger after the beam has moved on to another spot, then you do want to take a closer look at it. It should be blown strongly forward towards the front of the machine.

And some materials flame up worse than others. (Always a good idea to watch it closely for a bit on unknown materials. If you need to stop the print, just open the lid for a fraction of a second and close it. It will cancel the job.)


I’m sorry that your ran into trouble with your Glowforge while printing. If possible, could you share a video with us showing what you see when this happens? Also, please let us know the time and date the print in your video was run and we’ll extract the logs to look into this further.

That print was 10/27 at 10:30pm. It was just after i cleaned the fans. I will start it tomorrow to catch a video.

When it flames up its usually pulling towards the front of the machine. And it does go out but it occasionally burns and distorts my material. I am a small mold making business owner and the edges looking like that does not look good.

I shortened the video i did take at the time of the cut to upload it.

Unfortunately, the only thing I can see is the audio portion of your video. Maybe load it to YouTube and provide a link here?

What material are you making the molds from?

Another common issue is that the slightest film on the lenses/windows fuzzes the power and creates more smoke that cause it to catch, especially when traveling to the front. Of course there is often just different things going on in the wood itself. When the flames happen it also blocks the laser and it will not cut as deep in that location.

I make my molds from acrylic

Looks like a material issue to me. In other words, normal.

If that isn’t Proofgrade material, support isn’t going to be able to help.

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Is that thick acrylic? That does tend to flame up a little more than medium, because the speeds are a little slower.

It looks like the air assist is blowing the flame out sufficiently, so it appears you’ve got good air flow to me, but let support take a look at it. :slightly_smiling_face:

The burn marks appear on the masking when the air assist is working correctly. (It’s why we use masking on woods…it keeps the cut clean and we just toss the masking. So that is okay too. Some materials will show that deposit, others won’t.)

The damage on the edge of your acrylic is hard to avoid…the thicker the acrylic, the slower the cutting speed and acrylic tends to melt at the edges. You can try speeding up the cut and doing two passes, but you might want to let the cut edges cool for about half a minute before running the second pass. You’ll get more comfortable with it as time goes on and you figure out what works best for each material…but I don’t see anything unusual going on with the cut itself.

its 1/4 acrylic… been using the same acrylic company sense i got the machine in july and never experienced flames.

thats good to hear that i have good air flow. I feel good about it blowing the flame and not full on bursting into flames but i feel like im not far from a full out fire.

thats sad.

Acrylic is more likely to flame in my experience.

But I think your rear fan is not as clean as you think it is. Check that the scoop part is also clean - that is where I find a lot of gunk on my machine.

the scoop part?

The part that directs the air forwards on the bottom of the carriage plate, under the fan.


Yep, as eflyguy says

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I have a piece of 1/2 acrylic that cuts nicely, but there are certain spots that
flame and deposit soot on the covering. It could be due to some kind of inhomogeneity in the casting in process.


There are three fans. 1 behind and under the head blows into a scoop that goes directly under the head that is responsible for blowing out flames. It’s easily missed if you don’t already know it’s there.

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On occasion household or shop dust are microscopic or almost go totally unnoticed by our eyes and yet they become fuel for flames. What I do with all wood before a burn, masked or not, I run a lint roller over it to pick up any lint. I have even seen a human hair catch fire that escaped my roller once. Just an idea, but using a lint free cloth to brush any minute residual dust off your product may help. Even my proofgrade MDF sitting in my shelf gets basic dust, and since we do not live in a dust free world, it’s worth a shot.

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