I used the Makezine design as a template, but made a smaller hobo stove using two more easily obtainable (and used) food cans.
The cans I used are typical food cans: a 16oz and a 22oz can.
One end of the BBQ beans can had already been removed (for bean extraction). I dremelled an opening in the other end, slightly smaller than the second can. I smoothed the rough edges of the opening with a round file, then with pliers I bent up the remaining ring of the can lid, causing it to break into a ring of 'tabs' that the smaller can could more easily push through.
I drilled the holes in the can walls and bottom of the smaller can roughly as directed in the Make tutorial.
When the cans are assembled, the lip on the top of the inner can rests nicely on the tabs formed by the lid of the outer can, preventing it falling back out.
I broke-up a piece of kindling, into half inch square woodchips, so they would easily fit into the stove and fall below the air holes. My experience is the wood should not be near the air holes at the top of the stove.
To start the fire, I used the boyscout trick of rolling two cotton balls in Vaseline, then lighting with a spark from a fire stick. I loaded a few wood chips in, to buildup the fuel source, just below the ring of airholes.
You know if this stove is gasifying (I think) when you see flames jetting out from the air holes. The flames shouldn't really be coming off the wood at the bottom of the inner can. REMEMBER: the wood is supposed to be Gasifying not burning.
With my single stick of kindling, I was able to heat enough water for a cup noodle. Normally, it would take several time that amount of wood just to get a fire started, before even contempating using the fire for cooking. So I think this design is a huge improvement in efficiency over an open fire.
As the photos show, I did also make a pan rest with a tuna can. However, this didn't work. If I placed a can directly on top of that, the fire would extinguish. I had, instead, to suspend my pot of water an inch or so above the stove. If anything, I noticed that I was getting a secondary burn in the tuna can, which suggests perhaps that I was generating more wood gas than the lower chamber could use.
What's also nice about this stove is it's incredibly easy to put out. An extra safety feature! As I said before, when I placed the pan directly on top of the stove it starved the fire of oxygen and extinguished it.
WARNING: Never leave an fire unattended. Just because it looks like it is out, it may still be hot enough to restart itself. By fire safe and properly put out your fires.
I'm not sure what the physics is for this configuration of containers that make this a gasifying stove.
I've read that there is a restricted airflow around the wood, preventing it from burning, and so allowing it to smolder and gasify.
I assume that the narrow space between the two cans causes a rapid updraft that brings oxygen to the space above the wood, where the wood gas is accumulating. I'm not sure if some of the air entering the inner chamber is heated and sucked down to heat the wood to maintain the gasification. My understanding was that warm air was needed to flow over the wood to keep it gasifying.
© 2015, Webooma / Rik Sagar