The holes on my can were further from the bottom than suggested, but it gave me the option of filing the holes bigger, plus it created a lip which might help to hold in stray coals that found their way into the can. I wanted to drill 12mm holes, so I made marks around the circumference that were approximately 18mm apart:
I then centre-punched each mark to create an indentation to start the drill. To support the can while punching, I lay a heavy pipe wrench on the edge of my bench to create an 'anvil' to punch against. With the gentle hammer blows used in this case, the wrench didn't jump about too much, but care is needed:
I drilled the holes in three stages. I used an electric hand-drill and started with a drill bit maybe 4mm in diameter. Then I followed up with an intermediate-sized drill... then the 12mm drill. Great care is needed to ensure that you don't harm yourself with the drill. Drilling sheet metal at any time can be hazardous, but stainless steel is one of the worst things to work with. You can buy special sheet metal reamer-type drills which don't grab as much, but I used sharp, ordinary high speed steel twist drills at a relatively low speed. If you have to hold the can with one hand, wearing a sturdy leather glove is a good idea. If you have a vice, you could have a bit of wood protruding from the vice which the can could sit over while you drill. Safety glasses should be worn while using an electric drill. The edges of the holes will be bent, rough and sharp, and these can be hammered flat then smoothed with a fine file. A chainsaw file is good for this. If some of the holes end up a bit out of line it isn't the end of the world.
I cut the hole in the lid by first driving an old knife through it with a hammer against a block of wood. I made an 'x' pattern with the knife, then lifted up one of the resulting triangles so I could insert my small curved tinsnips to cut out the circle. The instructions indicate that this hole should be around half the diameter of the inner tin. If you don't have tinsnips, then maybe you could drill a ring of small holes and use a cold chisel to cut the webs of steel left between the holes (done while the lid is sitting flat against a soft steel anvil of some sort). Or if you are using the bottom of an ordinary tin can you could simply use a knife if you are careful. Safety glasses should be worn for this operation too.
I used a fruit can for my inner tin. I would have preferred a stainless steel can, but I couldn't find one. But the ordinary can was a pleasure to work with compared to the stainless. All you need to do with the inner can is to ensure it is the right size (cutting it down in length if necessary), and to make a ring of holes around it. The instructions say these holes should be 4 mm in diameter, and a formula is provided which gives the height for the centre line of holes from the bottom of the can. So you need to mark a line around the circumference of the can. The distance from the bottom of the can to the line is equal to the height of the top of the holes from the bottom of the outer can plus half the diameter of the air holes in the outer can. I simply pushed a sharp awl through the can to create these holes. It worked beautifully. I placed the holes as close together as possible around the circumference. I made the holes slightly larger than the awl by rocking the awl around when pushed right through.
Here are the three pieces which make up the complete stove. The only holes in the inner can are those in the one ring around the circumference (this inner can has no lid, and there are no holes through the bottom of either can). Also shown is the 'firewood'. This was gorse cut to a length of around 75 mm. The instructions imply that the fuel should not be stacked in the can higher than a certain point. This point is the same distance from the top as the holes are from the bottom:
There is blood on that firewood. I haven't cut myself with a hatchet for years, and I was taking a risk. I had a comparatively gentle reminder that I need to follow rules for safe wood splitting. Here is the wood stacked in the can:
I kindled the fire by laying paper and a few small slivers of wood on top. Lighting at the top is an important part in the operation of this class of burner. It should burn from the top down. I was very impressed with the results. I haven't done any serious tests, but this small stove appears to burn for maybe 20 minutes with one load of wood, so it isn't really big enough for my requirements (the current inner can is 75mm in diameter, and not very tall). I found that small bits of wood could be added successfully while the stove was burning well, but when I put in more wood after the volatiles stopped flowing, all I got was a heap of smoke until the new fuel got hot enough to ignite. I don't think that new fuel could be added indefinitely, because the charcoal will build up in the can, but you can get away with adding a few small bits.
The stove burned very cleanly, although it did blacken the bottom of the 'cook pot' as expected. The outer bottom part of the outer can remained comparatively cool most of the time, but it would be foolish to sit the stove directly on to flammable vegetation or other materials.
Here is the charcoal left afterwards. I tipped it into water to extinguish it. If I hadn't extinguished it it may have 'gone out' by itself, but it was glowing in some places. Note that the outer can doesn't have much discoloration, but you can see that the inner can has been really hot. There is also plenty of 'black' on the bottom of the pot.
I'm now keeping an eye out for larger cans to make a stove which will burn longer on one load of fuel. I'm inclined to think that although I could use cans which are slightly wider in diameter, it may be better to go for more height to make the 'top down' burning last longer, to ensure that the sides of the inner can stay relatively hot for heating the incoming air, and to ensure that enough air can reach the fire from the small holes through the inner can wall.
This is a great little stove. I wish to extend my sincere thanks to World Stove for getting me started.
Best wishes from Nelson, New Zealand.... Stephen Coote.
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