Wood-Gas? ... when wood burns it gives off different gases and residues (it's what makes your pot sooty). Some of these are combustible but are often wasted. A wood gas stove uses some of these gases and ignites them in the form of a secondary burn, meaning less fuel, more heat and less black goo on the bottom of your pot ... oh and your fuel's free too.
Okay then, off you go and have a rummage in the bin. You're looking for two steel tins, one with a bigger diameter (10mm -20mm) than the other. If you're feeling posh you can even give them a wash and take the labels off.
|Tin cans ... tougher than you think.|
The first job is to cut a hole in the bottom (this will actually be the top of your stove) of your biggest tin. The hole wants to be about 10mm smaller in diameter than that of your smaller tin. A hole saw would be very handy about now but I'm sure you'll muddle through.
|Small inner tin after shortening.|
Put the big tin to one side ... now we're going to butcher the smaller one. The first job is to remove a portion of the top (open end). How much isn't crucial but somewhere between 25mm to 50mm will work fine. Use the grooves in the tin as a gutting guide.
|Bottom of small tin with air holes added.|
When you've done that, flip it over and drill some air holes in the base. Again and quite surprisingly these don't have to be accurate or precise. A 5mm or 6mm drill will work fine. The holes will feed air to the inner fire so they don't want to be restrictive but if they're too big your fire'll fall out of the bottom!
|No measuring or drawing impliments were harmed in the making of this stove!|
Now put it to one side and turn your attention to the big tin again. We need some large(ish) air holes in the lower portion of the tin. 10mm to 12mm holes will work well here, feel free to use a drill rather than a knife and fork (as per picture). If you would like your holes to be round then hold a piece of wood on the underside of the tin while you drill them. Depending on the size of your tin and your drill, you should be able to get about 8 evenly drilled holes around the circumference.
|Air holes at top of inner tin.|
Locate your small tin again (if you haven't already stood on it) and drill a series of holes around the upper circumference (the end you shortened). The size of these holes will depend (a little) on what size drill you used when you drilled the holes in the base of the big tin ... make these holes half the diameter of the bigger ones. Aim for 8 to 10 equally spaced holes, set about 10mm down from the top edge.
|6mm hole in outer with inner tin in place.|
Next, drill 2 6mm holes in the in the big tin. These holes want to be on opposite sides of the tin. They also want to be in a location where the small tin will blog them when the smaller tin is placed into the bigger one.
Place the small tin into the big one ( the shortened end of the small tin faces up ... if you wondered). Hold it firmly in place and mark the small tin through your 6mm holes. Take it out and drill through these marks with your 6mm drill.
|Stainless! ... I must have gone mad.|
Put the 2 tins back together (so the holes line up) and with 5mm bolts fasten the inner and outer together. Don't go mad tightening the bolts or you'll crush the tins ... nylock nuts are a good idea. The nylon inset will obviously melt but it'll still stop the nut loosening.
|Nearly finished ... feel free to take the time to make yours nice.|
The inside of your stove should now look something like this ^. Inner air holes at the top, nut securing the 2 tins and 'grate' holes in the bottom.
|Pot stand fashioned from the remnants of your small tin.|
Hopefully you've still got the bit of small tin the you removed earlier because this is going to make your pot support. Split it top to bottom, then cut a couple of inches from the circumference. Now drill a series of holes in it. With a little 'bending' you should find that it fits quite snugly into the lip on the top of the stove. When you're not using it, you should also find that it clips nicely around the outside of the stove.
|This rough and it still works.|
That's it, your finished stove. All that's left is a test run ... once it's warmed up you should notice that jets of flame start to appear from the top holes in the inner wall. These flames are the (previously) unburnt gases igniting when they mix with the pre-heated air entering between the 2 walls.
A small handful of dry twigs should be all that's needed to boil a litre of water. Obviously you can keep feeding the stove with twigs if you need it to burn for longer.