Pleated conical alky stove
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This stove has been discussed in a couple of threads here in the past couple of weeks, but I thought I'd post a few pics and a video of it in action. Nothing special really, except it's total ease of use, simplicity in design, and it only weighs 3g.
It started out as a 12oz red bull can. The 12oz can is a smidge larger in diameter than the 8.3oz cans, allowing for a tough more fuel volume/spill resistance. I cut the can down to 1.5" tall and deburred the edge on some scotchbrite. Then I marked 12 even spaced liens with a sharpie and using a small screwdriver (anything about 1/8", 3mm for you metric folks, diameter would work) started making the inward creases on each mark, pressing while supporting the inside on either side on the mark with my fingers. Then I did the same in between each of those 12 inward creases, but pushing outwards. I first did not use the screwdriver, but this generated sharp creases that cracked before the stove reached its final shape. Using the screwdriver as a mandrel creates smooth radii. Now, I formed the stove about 50% of the way to its final shape before punching the pre-heat holes. I found that forming the stove's pleats after punching the holes ends up with a badly crumpled stove, but ymmv. You can vary the number and the up and down location of the pre-heat holes to tune the heat output of this stove to your liking. After the holes were punched I just carefully and gradually squeezed the stove between my fingers to get it to the right taper. What that is, I don't know- I just did it until it looked good.
Until now most efficient stove was my knock off of the mbd nion, but it's 12g (not that 9grams is really that much to be a deal breaker) but it's much, much, more difficult and complicated to make. It requires pressing cans together, drilling hole, inserting rivet nuts, etc… Filling it with fuel is slow and frustrating, and then it requires priming which is always hit and miss, especially in daylight. Too much priming fuel and the thing goes nuts until it burns off, too little and it goes out- and in daylight there's no easy way to know if it stayed lit…super annoying. This is a reasonably generous fill port, and all you do is light it and start cooking. IMO, this stove solve all of the issues I have with the pressurized stove I've been using, without any drawbacks.
I'm getting pretty consistent 10 – 11 min boil times on my Heineken pot, and around 13min burn times on 4tsp (2/3oz or 20ml) of fuel under controlled conditions. In super cold (about 20f) conditions it took about 17 mins to achieve a boil, but didn't need any more I always overfill a tiny bit to err on the side of caution. I think it would have performed better if I had something under the stove to insulate it from the cold ground. I'm also certain, though I haven't tested it yet, that boil times would be much faster on a larger more efficient pot.
Anyway- here are some pics…
apparently I don't know how to embed a video…so here's the link
http://vimeo.com/34376514BM
Yeah, just one single walled can. As far as I know, red bull cans are the same thickness as a normal soda can.
It's a 1/16" fiberglass cord from McMaster Carr. A long while back Tinny at Mini Bull Designs was wrapping his Heineken pots in it and posted a how-to. It's serves multiple uses- built in pot holder and a spare 10' of cord should the need arise. Now that I've been following your studies into the emissivity of the aluminum cans, I wonder since my windscreen goes all the way up the sides of my can, if my setup would be more efficient with less wrappign and painting more of the can black…
As for a crimping tool- I keep thinking of a tool like what they use to reload shotgun shells. You could drop in the cut down can, and pull one handle forming all the pleats one one perfect motion. But then, you are talking about hundreds of dollars, at least, of tooling to make a product that's worth a few cents? It's hardly worth the roi.
I'm a mechanical designer by trade, and have been called McGuyver and Tim Allen on occasion by my friends. My mind quickly tries coming up with methods that would improve the production my my myog projects, but when you add it all up, I'd end up spending far more than just purchasing a commercial product which in many cases would be a better product that what I could produce, especially as a novice at whatever it is I'm trying to make.
The one big exception is alcohol stoves. There's almost zero cost in materials and tools. The only think I have bought specifically for stove making is aluminum flashing and a 1/16" diameter hole punch for $7. Everything else is just stuff laying around the house. (wait- and reflectix for pot/freezer bag cozies).
BM
Perhaps you could get closer to cone performance by using the trangia idea of a pot lid wider than windshield, with a down-faced rim (eg use a foil pie/flan dish): this forces hot air to do a 180degree turn to exit.
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