“Good judgement comes from experience, and experience comes from poor judgement.” – Rita Mae Brown

I’ve been 3D Printing now for a couple of years. I’ve burned out control boards, hot ends, connectors on heating elements like the rest of us. But the other day something happened at around 3am on a Friday while I was up late working on a 3D model and printing some parts in my workshop downstairs.

My Anet A8 caught fire.

I don’t mean it got hot, or there was a little bit of a flame… it was engulfed:

This is a photo of one of my two ANET A8 3D printers shortly after I walked into my workshop smelling plastic to discover the entire left side of the frame engulfed in flames. Thankfully I was wise enough to install a fire extinguisher in my workshop and was able to put out the fire before it got out of hand — but it is terrifying to think of what could have happened if I wasn’t home or sound asleep.

With the fire out and everyone and everything under control the first question I asked was “How the hell did this happen?!” I’m sure if you’ve been 3D printing for any length of time you’ve heard the horror stories about cheap chinese parts, and trust me I’ve had more than one bad connector get hot and become a fire hazard. But how this fire started was different and there are a lot of lessons to be learned from it for my fellow 3D printing friends worldwide.

The Evidence: How my Printer Caught Fire

Before I explain how my printer caught fire, let me explain how this printer was configured and the upgrades it had at the time of the fire:

Upgraded Hot bed using a 110V silicon heating source and a 10A Solid state relay to turn it on and off (I used the original thermistor still to measure temp of the hot bed)

A thermal-conductive silicone on top of the hot bed and a piece of glass on top of that

An X-axis chain carriage to keep the wires on the extruder from straining unnecessarily

A standard ANET 1.0 control board running the default firmware

A full-circle cooling fan for the hot end 3D printed in ABS

An upgraded cooling fan that moved more air

An upgraded thermistor for the hot end that screwed into the block rather than being held in place with a screw

An upgraded 30A power supply

Everything else was standard. So I’m sure there are going to be those who read that list and immediately are going to want to chime in and tell me which particular upgrade (or lack thereof) is what caused this incident. Chances are though all of those theories are probably wrong!

What happened to my printer was caused by a combination of events that I think should give anyone who owns a 3D printer a moment’s pause. In my case a lot of the things that are commonplace considered “upgrades” and “safety related” nearly burned my house down.

Where the Fire Started

It took me awhile to figure out where the fire started. Once the printer was cool enough to handle (or what was left of it), I started looking around to try to figure out what caught fire.

Was it the power supply?

Faulty cheap power supplies are always a good guess when one things of how a fire might start. But nope, wasn’t the power supply! The entire right side of the printer where the supply was had no damage to it at all.

Was it the control board?

In the world of 3D printing it is a well-known fact most vendors of open source hardware like this use cheap components that are not rated for the job they are to do. This generally happens at the connections, where a little bit a resistance and a lot of current causes the plastic connector to heat up, melt, and eventually can start a fire.

But that’s not what happened here either. It’s a little hard to see from this photo but the high-power connections of my control board actually didn’t get damaged. In fact it looks like the control board was damaged by the fire, it didn’t cause the fire:

Was it the Hot bed?

I did have a serious hot bed installed on this printer, a 110V 200W silicone mat attached to the bottom of the aluminum bed is certainly a suspect. But when I examined the bed, other than the damage done by melted plastic and the fire the silicone mat itself was still in perfect condition, as was the wiring for it.

How did the fire start then?

If it wasn’t the power supply, control board or heated bed then that really leaves only one option: The hot end. Check this photo out, taken as a profile picture of the printer looking from the left Z-axis to the right:

This gave me my first real clue as to what produced enough juice to start a fire — look at the heat element just dangling there by itself! It should be securely inside of the hot end block but it’s completely free. It seems that this is the likely source of the fire. It would seem that the heating element managed to shake itself loose without me noticing. That was the “triggering” event that set off a whole chain of sorry. I normally run Marlin on my ANet but I had also recently replaced my control board, so at the time the fire occurred I was still using the stock firmware which does NOT have thermal runaway protection (which is when the firmware automatically shuts the whole system down if it detects strange temperature readings like when the hot-end falls out).

Okay, so we know where it likely ignited, but how did the fire spread to the point where it caught the entire frame?

That’s where things get interesting.

How the Fire spread

I print a lot, like most people, with PLA. Because of this I was sure to upgrade my printed with a full-circle fan duct that completely surrounded my hot end. Of course I printed this in ABS so it wouldn’t melt. But ABS certainly can melt and catch fire, especially when you put enough heat on it.

So when the heating element for the hot-end came loose, I suspect what happened is it managed to get itself wedged between the block and the fan duct and that’s where the fire actually started by igniting the ABS.

Once the Fan duct caught, it was in a perfect location to spread as it climbed up the fan duct, ignited the other ABS parts I had printed for the filament cooling fan, and I suspect eventually completely engulfed the extruder. As it burned chances are pretty high the extruder itself stopped moving (as you can see from the photo it died in the middle of the bed) — so how did it spread to the entire left side of the frame and nearly burn my house down?

Remember the X-axis chain I had installed, in large part to keep the wiring to the extruder from moving around and starting a fire? Well turns out when you have an ignited pile of ABS directly below the chain it doesn’t take much for it to catch fire as well — which is exactly what it did. If you look at the photo from the fire you’ll notice on the right side what’s left of my yellow-and-black x-axis chain.

This chain basically acted like the worst 3D printed fuse for lighting your house on fire, and the fire used it to travel across to the left side of the printer. It eventually made it to the mounts where it attached to the frame on the left side and caught fire to the mount for the X-axis stepper motor. As it burned it dripped fire-plastic on to the frame, and eventually set the entire acrylic on that side on fire.

It’s about at this point I smelled something and walked into my workshop to discover a 3-alarm fire.

Lessons learned

There is a LOT to learn from my unfortunate experience nearly burning my house down, and I strongly encourage all of you to take heed to my advice because any one of these things maybe wouldn’t have stopped the fire (there really was one thing that could have done that), but it was a combination of these things together that caused this accident.

Smoke Detectors / Early Warning Systems

This really should be more obvious than it was for me. Install a smoke detector, directly above your 3d printer setup. Stop reading this blog post, click here, and order one for your printer – right now.

Secure your hot end, and then secure it again

This fire would never have happened if the heating element of the hot-end hadn’t managed to get loose. On an ANET A8 the hot end slips into the block, which you then squeeze to lock in place using a screw you tighten in the block. I’m very much not a fan of this design, and would rather see a heating element you could screw into the block so it can’t come out. I haven’t found that design (yet), but there are a few things you can do to make a real impact on preventing the problem I had before it started:

Make sure the heat element is secure, often: Check it every print, or at least try to remember to if you don’t want to burn your house down.

Wrap your hot-end with heat-tolerate material: This is typically a suggestion for people who are having trouble keeping their hot-end at a certain temperature to insulate it. It’s great for that, but if I had wrapped my hot end I might have had an added layer of protection from it slipping out.

Don’t use fan ducts that are certain to catch your hot end and ignite it if it comes loose

When you get a stock ANet A8 it comes with a silly little fan duct that seems like it won’t do much to cool your prints. That’s true, but if I had had that fan duct instead of my upgrade I probably wouldn’t have almost burned my house down (the hot end would have flopped around but I doubt it would have stayed in one place long enough to ignite anything). I’m going to go for half-circle fan ducts that still provide decent coverage (and use an upgraded blower fan), rather than a fully enclosing one for exactly this reason.

For that matter, just be careful in general with how much plastic you put on your extruder in general. One thing I’ve realized from this experience is this: While it’s great to 3d print upgrades to your extruder, you’re basically adding a bunch of plastic-fuel right next to a heat source and to some degree just begging for it to catch fire. Be careful, and try to think about what would happen to your extruder rig if the very bottom was to ignite.

Do not print using the default firmware

The stock Anet A8 firmware (I’m honestly not even sure what it ships with) is the digital version of a loaded gun when it comes to fire safety. Probably in an effort to make the printer more forgiving to beginners, the stock ANet A8 doesn’t seem to have any thermal runaway protection at all and will keep right on printing even if the temperature readings don’t make sense! If I had been running Marlin, perhaps the printer would have noticed it kept trying to get the hot-end to temperature but the temperature wasn’t responding appropriately and halted before anything got hot enough to ignite.

Have a fire extinguisher within arms reach of the printer

I saved my workshop, if not the entire house, by having at fully charged fire extinguisher next to the printer setup. Click here, buy it, install it near by as soon as it arrives.

Be wary of carriage chains

I’m not going to tell you not to install a carriage chain, because they are really great cable organization tools for your printer. However as you can see from what happened to me, they also add a lot of plastic to your printer just waiting to be the world’s worst fuse to burning down your house. Since one of the points of good cable management is to prevent strain on wires and consequently possibly prevent an electrical fire, this one is sort of a catch-22 situation. I’ll probably still use them, opting to do everything in my power to keep the integrity of the hot-end in-tact instead.

Rethink your workspace

This whole experience has also made me question how I set up my workspace. Like so many others, I installed my 3D printers in furniture from Ikea — in my case a large wardrobe with nice slide-out shelves to house my two ANet printers. But after seeing what a 3D printer fire can look like I realize I basically put the printer inside of a burn-my-house-down box. I know when you are printing in ABS everyone wants a nice enclosed printer, but either do it in plastic or use a silicon mat to get your heated bed up to temp. It’s not worth the risk of burning your house down to prevent some ABS curling.

So what’s next?

Well, I guess I’m going to have to get a new printer of course. I’ll start by digging through the carnage and seeing what, if anything, I might be able to salvage. Since the fire was really limited to the left side of the printer I should be able to save my solid state relay, and maybe even my 110V silicone heating pad. The PSU is also probably in good working order still (I’ll run it through its paces on my workbench). Two of the four stepper motors are probably 100% fine, as is of course the LCD screen itself.

In the meantime I still have another ANet A8 that I’ll be immediately checking the hot-end of (and replacing the full-circle fan duct of) while I wait for a replacement.

Safe and fun 3D printing to everyone my friends. I’d love to hear your thoughts and comments on how you make your printer and yourself safe from the sort of disaster I only narrowly avoided. Finally, enjoy the collection of the wreckage below!