Cheap Flamethrower Is Predictably Worrying

We’d never criticize somebody for coming up with a creative way to save a few bucks. In truth, pickings would be pretty slim around here if we deleted every project or hack where cost savings was a prime motivator. That being said, there’s still some things you should probably spend a few extra dollars on. You know, the essential things in life that you need to know will be safe and reliable, like your car and…your flamethrower.

While we don’t have any information about what kind of car [Steve Hernandez] is driving, but over on Hackaday.io, he’s posted some info about his 3D printed wrist-mounted flamethrower. The final result does look pretty impressive, but given the subject matter and the lack of any safety gear, we would firmly plant it in the “Don’t try this at home” category.

At the heart of this flamethrower is a solenoid valve recovered from a Glade air freshener. Rather than spraying out the smell of lilacs, this valve has found a new purpose in life by squirting out butane from a pressurized can. The butane is then ignited by a spark gap made up two nails connected to a 300 kV boost coil.

[Steve] designed the frame of this creation in OpenSCAD, and printed it out in a single piece. It holds the butane can and solenoid in position, as well as keeping the nails in the proper orientation for the spark gap to function. Admittedly the head of his printed flamethrower does look very cool, but if there was ever a situation where you should be suspect of the heat tolerance of 3D printed plastic, a flamethrower is probably it.

What’s noticeably lacking of course is any method to keep the flame from potentially traveling back up through the valve and into the butane can. The high-speed flow coming out of the nozzle is probably enough to keep that from happening, but we still wouldn’t feel comfortable strapping his device to our wrist as-is.

You may be surprised to find that wrist-mounted flamethrowers are a relatively popular project here at Hackaday. We’ve covered quite a few over the years, but still aren’t convinced this is something we personally need to add to our collection of gear.

35 thoughts on “Cheap Flamethrower Is Predictably Worrying

  1. > What’s noticeably lacking of course is any method to keep the flame from potentially traveling back up through the valve and into the butane can.

    Wouldn’t that require oxygen in the butane can?

    1. Yeah. This is probably an area where a little irrational fear is healthy, but flame won’t shoot into a pressurized vessel the way it’ll follow gasoline up a spout into a jerry can. Probably fine, and besides: singed eyebrows build character. My grandad told me so.

    1. Yes, this was also my first thought when I read this. :-(
      The other nonsense are the “300kV”. Nothing on this small boost coil would sustain real 300kV. Sometimes they are even marketed as “400kV”, with even thinner insulation of the HV wires. :-) And with the warning to keep the wires less than 20mm apart to avoid damage by overvoltage.

    2. I think he meant that the flame can get back to the nozzle, melting it, and then things start going pear-shaped. Unless this can uses a metal nozzle, I can’t tell in the picture. I’ve definitely seen ones with plastic nozzles though.

      1. Even in the nozzle, there is no oxygen for the butane to burn, and the nozzle is continuously being cooled by expanding butane. Rather than melting, I’d worry about the valve freezing up, keeping it from closing/

        1. In the valve is no water stuck, so it can not freeze up. But i can imagine, that it could distort while melting to keep it from closing. Anyway, there is a metal nozzle in the 3D printed part – that shifts the question, how long this stands to teh heat.

          1. Water from the air can condense on the valve and freeze solid. It’s probably not going to be an issue, but I think heat isn’t going to be an issue either, because of the cold butane flowing through it.

            The plastic holding the nails might melt, from a combination of heat conducted through the nails and radiated onto the plastic by the flame. Maybe a little aluminium heatshield could prevent that, or if you only use it in short bursts, it won’t even be a problem.

            At least this is a spectacular way to light the barbecue!

          2. Like Sparky mentions, water can condense and freeze up ‘on’ the valve, and in the crevices, not inside it. I’ve had this happen on me on green gas (which is essentially butane) with metal nozzles for Airsoft guns. The o-rings would tend to freeze and contract causing a slight leak until things warm back up again.

          3. The issue isn’t necessarily water freezing around the valve, it’s the gas itself freezing inside the valve.
            @TacticalNinja
            Green gas is unscented propane with some (silicone) lubricants mixed in. Butane liquefies at too low of a pressure (~35psi / 2atm) for it to be a propellant in airsoft

    3. Yeah, there’s nothing to protect from the flame travelling back, just like there’s nothing to stop someone with shitty hands poisoning the entire cities water supply by using the faucet to wash them.

      Also, if you want to keep your white spray paint clean, never use it over a wet color in case it sucks back.

    1. You don’t want it to be conductive. Neither electrically nor thermally. So you need to make a gypsum negative, fill that with clay/ceramic matter and fire it. If that is too much effort, I would cast it with epoxy where generous amount of mineral filler (sand) are added.

    1. ahhh… very sharp, you are so right! It took a while for me to realize it, but you are right. Not everything that makes a flame is a flame thrower. But still, it is a dangerous contraption I consider it to be dangerous simply for the same reasons as I don’t strap a torch or chainsaw to my wrists.

  2. Every time this pops up I get the urge to McGyver one out of a caulking gun, a washer, JB Weld and a piezo igniter, and whatever wire/coathanger is around… and of course the can of butane.

  3. Wow, just reading everyone’s comments here. To clarify a few things : It’s safer than it looks! The flame can’t travel back into the butane can through the solenoid valve because it’s a pressurized gas, also – Butane needs oxygen to burn, and there is no O2 inside the can itself. I use a 35mm brass tube that connects the end of the solenoid to the front of the flame thrower. After using it for 10-20 seconds, the brass tube is actually frosted over because the expansion of the butane has a cooling effect (Boyle’s law). This in turn keeps the plastic tip cool. I’ve run into a little issues with the ABS plastic starting to get soft after 1-2 minutes of continuous use around the nails. To address this, I used a reflective aluminum tape to coat most of the front of the device.

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