Let’s build a robot that gets hot. Really hot — like three times hotter than McDonald’s coffee. Then make it move around. And let’s get the cost in at around $100. Sounds crazy? Not really, since that describes the cheap 3D printers we all have been buying. [John] found out the hard way that you really need to be careful with hot moving parts.

The short story is that [John’s] Anet A8 caught on fire — significantly caught on fire. Common wisdom says that cheap printers often don’t have connectors for the heated bed that can handle the current. There have been several well-publicized cases of those connectors melting, especially on early production models of several printers. However, this printer had an add-on heater with a relay, so that shouldn’t be the problem. Of course, a cheap power supply could do it, too, but the evidence pointed to it being none of those things.

The culprit seemed to be that the heating element popped free from the heat block. This made contact with the ABS ring fan (also, aftermarket) and from there the fire spread. A contributing factor was that [John] had just replaced the motherboard, and the stock firmware didn’t figure out that keeping the heater on wasn’t changing the thermistor’s temperature and shut down. Most firmware will do that as a safety measure.

We like cheap 3D printers and many of the Hackaday team have Anet A8’s so we don’t want to give the impression we’re knocking it or that we think you should quit 3D printing. However, this demonstrates the need for inspecting your hardware closely. If you don’t have an extinguisher near your printers, maybe you should. Leaving them completely unattended is probably not a great idea, either, although most of us have probably done that with a machine we trust.

[Elliot] did a great review of the A8. Sadly, we’ve covered 3D printer fires before, too.