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3D Printer Fire protection
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janoc:

--- Quote from: dnwheeler on September 30, 2019, 06:01:15 pm ---Working on medical devices for a living has taught me that most consumer products (especially cheap ones from China) don't have even the simplest forms of fault detection systems.

The 3D printer firmware should be designed to notice that the temperature isn't rising when the heater is on, and shut down the system. They should also be detect an open or short in the thermistor circuit.

--- End quote ---

That's exactly how it is implemented in the Marlin firmware (which most of these cheap machines use). Any abnormal value or the temperature rising slower than expected/falling when the heaters are on will trigger a panic and kill the print, requiring hardware reset.

However, thermistor faults are only one way how a printer can catch fire. For example, if a short develops you have a problem - the power supplies in these things routinely deliver 20-30A so something can go up in smoke easily way before a fuse blows (assuming that there is one - many machines don't have any!) or the overcurrent protection trips. Or the power supply could go bang on you. Or an axis stops moving for some reason (stepper driver failure, belt failure, ...) and the hotend cakes itself into a pile of molten plastic, eventually catching fire. Etc.

Running a cheap consumer machine unattended somewhere where a fire could cause major damage or a loss of life (i.e. home) is a terrible idea, no matter how many smoke detectors, fuses, cameras and similar are added.

That a print requires 16 hours to do is not really an argument anymore - most new machines are capable of recovering from a loss of power (Marlin 2.x feature), so you can just turn the thing off, go to bed and come back to it in the morning and continue. Of course that works only for materials that don't pop off the printing bed when it cools (e.g. PLA on the blue painter's tape) but it is still better than having a fire overnight.

3D printer is a machine tool and should be treated like one. CNC mills and lathes are not left running unattended neither and those machines are typically built much more robustly than a $200 Chinese 3D printer.
exe:
I'm going to put a fire alarm above the printer.
BillyD:
Domestic burglar alarms can support smoke detectors. I imagine it operates like any of the other devices (pir/reed switch/etc) on the system where it runs on 12V and opens a relay if the sensor is triggered.
One of those could fairly easily be linked to the printer supply to shut it off, sound an alarm, etc.

Whether it also needs to activate a sprinkler system, call fire brigade, etc is a whole other dilemma as your home-made device is now at least responsible for protecting your property and everyone in it!
How much do you trust it, is it rock solid, etc!

nixxon:
I recently bought a Sidewinder X1 3D printer made by "Artillery3D" http://www.artillery3d.com/. It is said that their designers previously used to work for various, competing 3D printer manufacturers. However the designers were not satisfied with how user feedback and reported issues were handled by their previous employers, so they decided to make their own gamechanger 3D printer that is supposed to punch above it's belt for a $380 3D printer (now $399). The X1 has a fast heating 110/220V heated bed (30x30cm), volcano nozzle, direct filament feed and thermal runaway protection and silent stepper drivers/motors to mention some of the good stuff. The chassis is also actually grounded :D The item was delivered at my door by DHL Express within a week (from Hong Kong) after placing the order, for a shipping cost of $8 (+ a local DHL customs declaration fee of $30, though (stuff is expensive in Norway)).

The 3D prints look really good, using some random PLA filament that I got from my local general hardware shop (Flashforge 3D printer spool of 0.6 kg PLA). Link: https://www.clasohlson.com/no/Filament-PLA-til-3D-skriver-Flashforge/38-7721-4

If you consider buying a 3D printer using Fused deposition modeling (FDM) I would check this one out. I got version 4 that has developed quite a bit compared to the initial release version that was introduced 1 year ago. If you buy, make sure you get at least version 4. Here is a link to the seller that supplied my unit: https://www.banggood.com/Artillery-Sidewinder-X1-3D-Printer-Kit-with-300300400mm-Large-Print-Size-Support-Resume-PrintingFilament-Runout-Detection-With-Dual-Z-axisTFT-Touch-Screen-p-1411501.html?rmmds=search&ID=48036&cur_warehouse=CN

They also sell it on Amazon and various other places.
CatalinaWOW:
While a fire is a theoretical possibility, it requires a sequence of failures.  Not something I am going to lose sleep over on my Ender 3.

1.  Initial failure of thermocouple etc.

2.  Software failure (this one isn't actually totally unbelievable.  While I believe the existence of temp slope detection, this must shut off after stable temp is reached.  Then some stack overflow or the like could open the control loop.)

3.  The hot end has to get to ignition temperature.  Again probably not a very low probability.

4a.  Fire has to propagate through bowden tube and up to filament reel to get enough flammable material to spread beyond printer.
4b.  Print head has to get hot enough to radiation or convection heat material around printer.

It is easy to eliminate 4b. by keeping flammable material away from the printer.  Far easier than adding yet another protective circuit.  So I have done that and stopped worrying.

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