Burning when lasering?

When I have been cutting recently I’ve noticed that my laser has been burning the paper layer a lot. The bottom sensors and lens keeps getting covered in black ash. At first I just noticed that some of the paper would be a bit scorched, but later I see it causing pretty large flames. I am thinking it may be a problem with my lens since the last time I cleaned it there was a large blemish that hasn’t been there before.

Before I replace the lens, is there some other part of the machine that would cause the extra burning/defocus? I am going to replace the lens since it looks damaged. But I don’t want to replace it and find out that it was caused by something else and ruin a new lens.

If that lens won’t clean off then it needs to be replaced. Check the 2 other windows on the laser path and the blue mirror inside the head. Do not wipe the blue mirror aggressively because it will scratch very very easily.

The flame doesn’t look like it is being blown forward by the air assist fan. That is the fan attached to the same plate as the laser head. Check to see if it is turning properly when the laser is operating. But not sure I would laser at all with that lens.


Thanks. I’ve stopped all lasering since I saw the flame coming out like that. I have already ordered a replacement lens, but I want to make sure that it is just the lens and not something else that would cause the lens to be out of focus. I think originally the lens got damaged because of smoke buildup on the lens from cutting…

1 Like

Yeah, agree with @rpegg on this one…You will probably want to check the air assist fan. That doesn’t look like it’s working correctly, and it will just cause the same issues with the new lens.

Not going to send you to the instructions until Support can take a look at it since it requires removing the carriage plate. Just wait to hear from them about it. They might want to have you replace the fan, but I’m hoping they can see it on the logs.


A failed or blocked air assist fan would cause build-up on the lens, which would then result in the damage you see.

It’s standard maintenance to check and clean it, here are the instructions:


Looking at the word “National” in the image I see soot but pointed down which happens if the fan is moving air at all if badly and looking at the rest the soot trace seems episodic. Are you using magnets at all? The fan especially has trouble operating in a strong magnetic field, and if you think about stuff moving in such a field this is not a surprise but rarely encountered normally.

If you are not using Magnets then certainly something else is interfering with the working of the fans, as even the tiny fan inside the head is supposed to keep smoke from getting near the lens. The white cable or just gunk clogging the fan would be the other most likely suspects.

If you turn the machine off and pull the gantry forward you should be able to see the main head fan in the back and it should be able to move without resistance.

This is what it should NOT look like…

I am ashamed to admit that after 16 months of having this laser, I didn’t even know that there was a fan back there. For some reason whenever I read “assist fan” in that past I thought of the little fan on the laser head assembly :man_facepalming:

I went through the assist fan cleaning guide and it was really caked and dirty. I used a compressed air can and it started blowing out chunks of built up gunk from the fan. The fan seems to be turning easily now and I’ve cleaned up a lot of the built up smoke on the carriage piece.

I’ve checked all of the other lens and windows and they are look clean and clear since I clean them fairly regularly. So I think once the new lens comes in a couple of days I’ll try printing again. Unless there are other steps I should do to check that it is working properly?


Just watch the flame when it’s running, it should be almost blown out and directed towards the front of the machine. (That’s great if a cleaning was all it needed.) :slightly_smiling_face:

Here’s a worst-case (very thick material - .59" weathered pine fence picket - that was incredibly flamey) that shows how the flame should look with a properly functioning fan:

Did you try cleaning your existing lens? Soak it for an hour in rubbing alcohol and then try to get the gunk off with your fingernail. If that works you can lens wipe it clean and should be good to go. Often that kind of buildup is just external stuff tgat has baked on and not damage to the lens or its coating.


I’m sorry that you ran into trouble while printing. It looks like you’ve already received some fantastic advice from our other community members. Thanks folks!

Since you’ve already checked your unit’s other optical surfaces and cleaned the air assist fan, the best next step will be to see if you’re able to print as expected once you receive your new lens. Please let us know how it goes!

Hello @zoramite, I just wanted to check in with you and see how your Glowforge is printing now that you’ve received your new lens. Please let us know if you are still having print trouble, and we’ll be happy to take a look.

Thanks for checking in. After cleaning up the fan it has been doing really good. I was able to also cleanup the old lens using the alcohol idea above, so I’m still using the original lens and it has been doing great :slight_smile:

1 Like

@zoramite I’m glad to hear your Glowforge is back to normal! I’m going to go ahead and close this thread now. If you run into any other trouble, please start a new topic, or email us at support@glowforge.com. We’re here to help!