By Sheldon Greaves
Way back when, making your own alcohol burner was a common early project for a kid eager to do chemistry at home. The bottle with the wick stuck through a hole in the lid was a common site in home labs.
Recently I became aware of a very interesting subcategory of “Makers.” These folks like to make lightweight alcohol backpacking stoves out of recycled materials, frequently discarded soda cans. These people have some truly inventive sorts among them. There are several pages with plans for various stoves. I found this one at http://zenstoves.net/ particularly impressive.
A year or so ago I tried making one out of two 12 oz. soda cans, plus some extra aluminum from a third can. The result was a remarkably lightweight little stove that burns quite well, stands about 1.5 inches high, and has the footprint of”¦ well”¦ a 12 oz. soda can. It isn’t adjustable, but it does burn alcohol, even drug store rubbing alcohol, although the higher the concentration the better.
Later I wondered if I could adapt one of these designs for use in a home lab. I wanted a smaller footprint, that would focus a smaller flame, sort of like a Bunsen burner. It could also be slightly taller, giving it more fuel capacity.
The basic principle is that you take the bottoms of two soda cans and slip them inside each other. Before you slide them into each other, you insert a cylinder of aluminum so that you form two chambers, one on the inside, and a narrow chamber around that. The cylinder is pierced at the bottom, and you cut a hole at the top, with jet holes.
You pour alcohol into the center chamber and light it. Some passes through holes in the cylinder into the outer chamber. The burning alcohol in the center chamber heats the vapor in the outer chamber, which jets out through the jet holes and burns much more efficiently.
To get my narrower, taller profile, I used two Red Bull cans, without dents. It’s easier to work with them at first if they’re full, so don’t get empty ones if you can help it. Sand them with fine sandpaper to take off the labeling. This gives them a better appearance, and makes it easier for one to slide inside the other. Polish the half that will slip inside with steel wool until the surface feels glassy.
Now you need to cut the cans. The half that slips inside will be the top end, and stand the full 3 inches. The bottom half should be about ¼ inch shorter. The easiest way to cut these cans is to set up a jig that will let you score where you want the cut with a sharp utility or hobby knife. Don’t try to cut all the way through. Two or three trips around should be plenty. When you’re done, empty the cans of their contents, and then use your fingers just above the score to bulge the metal outward. At the same time, press inward below the line. If you do it right, the metal will part easily, giving you a clean, smooth cut.
Meanwhile, find another can and cut off the top and bottom to get a cylinder, then cut the cylinder lengthwise and smooth it out. You’ll want to establish the height for your stove. I settled on 3 inches, so I cut a strip three inches wide. You’re going to make a cylinder that sits in the angular trough just around the bulge at the bottom of the can, and in the corresponding trough at the top. The circumference is 5 13/16 inches, but make yours one inch longer to allow for overlap when you form the cylinder.
I used ½ inch overlapping tabs to assemble the cylinder. Test fit it to make sure it rides where it should. For adhesive, I used JB Weld, mostly because that’s what I had available. It seems to work fine for this application, but there are doubtless other commercial epoxies that would do better. After the glue is dry, cut two small notches in the bottom, roughly ¼ inch wide at the base.
Now comes the most tedious part of this operation. You need to cut out the center of the top of the top/inside half. Taking a utility knife, start scoring around where the foot of the can changes to the bulge. I don’t know an easier way to do this, except to keep going round and round until the metal starts to give. Eventually it will open up and come apart. Smooth the edge with sandpaper or a small beveled file. Since this will need to slip inside the bottom half, make some cuts perpendicular to the edge to help it slip inside more readily.
Time to put it all together.
Mix up some glue. Put some glue around the bottom of the outside half, inside the trough where the cylinder will sit, and up the sides about an inch. Also put some glue in the top half where the top of the cylinder will go. Â Wipe the inside half with some vegetable oil or some other lubricant (I used some leftover oil from an empty bottle of marinated artichokes).
Put the cylinder into the bottom/outside half. Now insert the top half into the bottom half. Make sure you don’t bend or pucker the metal on either half. This is by far the most finicky part of the process, so you should do a little test-fitting beforehand. Once the pieces are started, press the top into the bottom until the are nearly meshed. Do a quick check to make sure the cylinder lines up with the top half, then push it home. Let the adhesive set.
Now, add the jet holes around the top as shown. I used a push-pin. They don’t have to be exactly symmetrical, and eight seems to be enough.
To try your stove, put in a little ethyl or other kind of alcohol. Light it. It will burn for a little while, looking sort of like a Sterno can. Soon, in perhaps no more than a minute, you will see tiny blue flames jetting out of some of the jet holes, and gradually they all will be burning. Occasionally the assembly will leave gaps between the inner and outer parts, allowing alcohol to jet out and burn. Those can be sealed with adhesive.
While I haven’t had time to test this burner more completely, it seems to me that it produces a hotter flame than a regular wick alcohol burner. It has enough capacity to run for a while. If anyone else builds one of these, let me know how it worked out.