Burning, burning, burning

Just posted on Facebook. Their only comment was ‘well, this sucks’… :grimacing: That’s putting it mildly.


A much more accurate comment than “the Glowforge exploded!”

That sux :frowning:


well, that’s enough fire damage that i feel pretty safe saying they left the room while it was running.


The degree to which the crumb tray itself was consumed suggests a pretty long-burning fire.

Can’t say I’ve never stepped away while my Glowforge was running, so I can’t cast stones.

It’s images like this that have me never leaving the room when cutting acrylic, though. And the reason there’s a fire extinguisher at the entrance to the room.

That’s a sheet of IPI brand acrylic coming out the passthrough slot.


Didn’t know a brand name, but that’s what I thought, too…that it looked like they had been cutting acrylic.


The partial “RA” in the photo is from the word “LASERABLE”. I recognized it because I have some of this on my shelf.


it’s a pretty safe bet that about 75% of fires are acrylic. especially the “my GF is ruined and the glass exploded” fires.

definitely not with acrylic. most times i’ll pause. i’ve run down the stairs and back up fairly quickly. but never long enough for something that damaging to happen.


I was thinking it looked like shiny melty stuff on the crumb tray. But yes I cannot think of having seen a photo where it was obvious they were cutting plywood.


i’ve heard of cardboard fires, and i’ve heard of sometimes people having masking catch on fire if it wasn’t adhered well. but every single time i’ve seen a tragic fire like that it’s been acrylic. it burns super hot and once it gets started, it accelerates.

wood tends to be more “smolder” and embers than super hot open flame. and paper/cardboard flames out so quickly it’s not going to do that kind of damage.


I keep waiting for someone to post about losing their house in a fire like this.

I think it’s not just acrylic but acrylic with overly-intricate or poorly formed cut paths, combined with low speed settings. I don’t find acrylic dangerous at all but then I never cut anything but simple shapes at relatively high speeds.

I’d rather do two fast passes than one slow one. I pretty much never go below about 190 speed with acrylic, my 1/8” settings are all two pass higher speed.




i’ve cut very thick acrylic on the GF. 1/2" thick. but very very carefully with many passes.

it’s absolutely the most dangerous laser-safe material there is.


You know, I think I agree. I’ve talked a few times here about the chemical energy in acrylic, I never thought to look it up until today, So:

Arcylic is 24.2 kJ / gram

Woods are a little harder to get firm values for, but most estimates put it like this:
Potential heat output of many hardwoods is in the vicinity of 19-20,000 kJ/kg

So, by this measure, acrylic is roughly the same energy density by weight as wood, maybe as much as 20-25% more

So now you think of mass. Density of acrylic is 1.18 g/cm³, maple is 0.63-0.75 g/cm³.

So keeping all that in mind, the chemical energy of a 1/8" sheet of acrylic should have about twice the combustion energy of a 1/8" sheet of wood.

Add to that, as @shop said, that the way each material burns is different – the melting/combusting/offgassing aspects of acrylic decomposition seems to mean that the fuel can be ignited more quickly than with wood… and yeah, that’s what kills Glowforges.

I’m speculating a bit here but this all feels about right. Be careful out there, folks!


Judging by that picture It burned down all the way. You would expect a smoke alarm to activate?
Reassuring that it was contained because it burned for a while.


the wort material for burning is foam, you definitly do not want to leave machine unattended while cutting foam


you could be right. foam has the same kind of high flammable / hot burn as acrylic but it adds in additional air gaps inside the material, which could make it more likely to catch, even if it may not burn quite as hot.


That’s because they know better than to say “I only left the room for a second… to fix dinner, wash the cat, mow the lawn and go potty”.

There truly is no excuse for this to ever happen. I stand next to my GF even if it takes hours to complete my project


I must admit I have left my GF VERY briefly while engraving acrylic, but keeping an eye on it via a mounted camera viewed on my phone, with phone in hand, but never while cutting acrylic. If it’s cutting, I stand right there and watch it. And I always stand right there with doing anything paper or cardboard. If it’s wood, I’ll be in the same room but not standing right there watching. I watch it with the camera on my phone, but I am only a couple feet away and walk over and visually check often.


I admit I have walked away from acrylic but never for engraves and only for cuts that I know aren’t pushing my luck. Seeing a picture like this is a good reminder to not get too comfortable regardless of what I think I know, though.

I think of plastic as frozen gasoline. In fact for acrylic, by volume it’s about the same energy, I just looked it up.


you’re probably thinking that backwards. engraving is a lower power/speed combo than cuts. cuts are riskier than engraves. but neither is safe.