Flame when cutting - is this normal?

Hello Glowforge Community! I have been using my new glowforge for about a month and more recently it has started to flame more than usual (see video). I have cleaned the glowforge, including the fans. Is this normal?

I can’t see your video because I have stupid Internet, but the first thing I suspect in such cases is the air assist fan. Have you cleaned it lately? (I know you said you cleaned the fans, but some people miss that one – it’s on the very back of the head carriage.)


The video is failing due to a bad codec. If you can upload it to youtube and send us a link to that it might solve the issue.

But… what @geek2nurse said is quite possible.


Your video is in a format called HEVC. It’s an Apple format that really only works on iOS devices like an iPhone or iPad. Most web browsers (including Apple’s Safari) do not support it.

The video is showing “flashback” – that very common and nothing to worry about. Depending on the material, the flame could be white, red, or blue. The main thing to watch for: it flames fast and should go out. If you see the flame beginning to burn the paper tape, then stop everything and blow it out! (I’ve only had “fire” when using thick acrylic and lasering right along the edge of the material.)

With some materials, the flashback could cause melting to acrylic or staining to wood. The tape will help with smoke stains. For melting, I usually suspend acrylic by 1/8th inch. Just lay the corners of your material acrylic on top of some scrap wood or acrylic. This allows it to “float” above the crumb tray. When you do this, any flame goes down and not flashing back up onto the material.


Works fine with the VLC player on a pc … just download the movie

1 Like

I don’t see any unusual flames in your video. I don’t see any flames at all, just the beam.


Thank you! I am glad to hear it’s nothing I should be concerned about and that it’s flashback. I thought it might be but was under the impression that flashback is typically found under the material and the machine only recently began to show this… so wan’t sure. Thanks again for taking the time to respond, I really appreciate it.

phew! thanks for taking the time to respond

Yeah, those look normal to me. Especially when cutting acrylic. That is why you need to keep an on it.


I see that the small, occasional flame is being blown forward, towards the front of the machine. That is good because it means the air assist is working well. That is the purpose of the air assist fan (located under the print head and blowing forward) … to blow out any flames and to blow the smoke and debris from the laser cutting the material.
It looks normal to me.
Maybe others will chime in.


There is wax in the temporary adhesive of that brown masking that comes from the manufacturer of the acrylic sheet you’re cutting. The flames that appear are the vaporized wax igniting before the air assist fan snuffs it out. Your Glowforge is working normally. That wax is presumably why Glowforge has the acrylic they sell re-masked with something else instead of retaining the masking the manufacturer usually supplies: Proofgrade acrylic won’t flame up as much, and this lets them warranty it against fires when you use their brand. I’ve never seen their white paper masking on acrylic from anyone else.


The thing I have noticed and mainly with wood when you get little candle flames, that location will frequently not cut all the way through. This is not so much an issue with the laser (though crud on a window or lens can cause it too) but more commonly something interfering with the airflow across the area being cut. Often when the cut is headed away from you. Less often when the laser is headed towards the front. Something like a bed pin or a drop-off at the edge of the material can do it as well. I often just toss in a piece at the same thickness so the airflow does not encounter that edge between the fan and the cut.


This topic was automatically closed 32 days after the last reply. New replies are no longer allowed.