While experimenting with early prototypes, it became evident that I wanted a pressure stove. Pressure stoves are more fuel efficient and they have fewer internal parts.I wanted something easy to build but most of all, I wanted a method that would yield consistent stoves. After learning the hard way, I decided that safety was to take precedence over those two requirements. Building a Hannah Stove will take you only one hour.
Lets get started with the requirements.
This last list is for polishing. You could do it with steel wool but that's a lot more work. With basic polishing equipment you will have a shiny stove in no time. If you go for the shiny stove, remove the paint from two of the cans before you open them. Use the sandpaper for that. Be sure to smooth the bottom where there is not paint as well. Use plenty of water to prevent the sandpaper from clogging. Don't overdo it. You only need to clean about 5cm from the bottom of two the cans.
Now would be a good time to enjoy a glass or two of your favorite soft drink. You need to empty the two clean cans before you proceed.
Attach the box cutter blade on top of the wood block so that it protrudes a bit. You will use the wood block as a guide to achieve a neat cut on the can. This is a tricky part. The Hannah Stove doesn't use glue or sealant. That means that you need to fit the parts really tight. You can only do that if the cut is really clean and straight. You will probably need to use a spacer to adjust the blade height. Find something to put either under the wood block or under the can so the blade is about 2.5cm from the bottom of the can.
To get a real clean cut, you need to push the can firmly against the wood block but only slightly against the blade. Technically, the vector of your force should be almost orthogonal to the side of the block and at most 20 degree against the blade. You then just rotate the can until the blade passes through. This will take at least 20 turns. You budgeted one hour for the whole thing, right? The final cut should be really straight with almost no bumps toward the inside. Minor bumps can be dealt with. When the blade goes all the way through at one point, it might start to jam when you rotate. You should be able to separate the two ends by wiggling them gently without more cutting. I mean, really gently; no bumps.
Once you have cut the two cans, it's time to assemble your stove. The Hannah Stove is press fit. If you have peace of mind, you can just align the can bottoms and fit one right into the other. It is easier to do that if you enlarge one can bottom a bit. That's what the third soda can is for. This can should still be sealed. Select the can bottom with the less inward bumps, this will be your stove bottom. You will ram the third can into it. The only way to take the third can out afterward it to use vapor pressure. Pour a few drops of water in your stove bottom and ram the third can in it. Of course, when I write "ram", I mean "really gently push downward". If it didn't get stuck there, you are all set. If it did, pour a few drops of methanol in a pan under the two jammed cans and set it ablaze. Both will just pop apart. That or the unopened can will explode. It doesn't happen often but for this eventuality you might consider replacing the unopened can with a can filled with plaster.
Before you lower the top of your stove over the bottom, drill the filling hole. If you don't, the air pressure might disassemble your stove before you are done, which is really frustrating. Start with 3mm, you can always enlarge later.
By now, if your favorite soft-drink is the same as mine, you should have peace of mind; you will need it for the next part. This can be really frustrating but if you followed all the instruction properly it will work, eventually. The top of your stove is a little bit smaller than the bottom. You need to lower it really straight into the bottom and to tap it gently until it fits mostly flush. To get it started, you can cut a section from the top a of can that you will use a guide. You need peace of mind while assembling any kind of zen stove, but especially while working on those that don't use sealant.
If you wreck one or both part, don't worry. You lost at most 20¢. Just cut another soda can and try again, with peace of mind and a stiff drink. When you finally get it, you can make the jets. The easiest way to have the jets aligned is to use a hole model. Made with the star tool in Inkscape. I set the number of arms to the number of jets that I want and the inner radius to 0.
How many holes you want depend on the size of your needle. A lot of small holes gives best result. I use 24. Fix your hole model on top of the stove. Blu Tack works well for that. Cut a needle and fit it in the X-acto handle. To prevent the needle from breaking, cut it so that it protrudes at most a few millimeters. You can enlarge your holes later with a longer needle.
Once you are happy with your jets, you can see if they cook well. With 24 holes, I use a 5.5cm high mesh pot stand. Depending on your fuel type and your hole configuration, you will want to play with the pot stand height. Making a pot stand will be easy. You just need to cut a strip of steel mesh. Folding wire works just as well. The idea is to play more with the pot stand because it is easier to adjust that the jets. You new stove should bring 500ml of water to a rolling boil in 6 minutes with 30ml of ethanol.
Once your stove is finely tuned, you should give it a good shine. Aluminum is really easy to bring to a near mirror finish if you use the right tools. The idea is to level the scratch pattern and to progressively reduce the scratch size until you have something close to the wave length of visible light. Aluminum is a soft metal and your stove is really small. You can move quickly from one step to the next.
You now have the ultimate stove. It is ultra light, good looking, dependable, safe, easy to use, efficient and you built it in only one hour, without fancy tools or measurements. Do not despair if it doesn't work well or doesn't look good the first time. It can take a few attempts to get it right.