06 December, 2011

Easy build penny stove (part one: building)

Following a discussion with my sister where we were bemoaning the power outages in a Scottish Highland Winter, I decided to make her one of these penny stoves as she has no alternative energy source to electricity, and could not make a cup of warming tea or even fill a hot water bottle.

Rolling Boil
At a rolling boil

Penny stoves or Pressurised Jet Alcohol Stoves to give them their proper name are easy to make and very efficient in operation. i.e. You can heat a lot of stuff with very little fuel. They work by heat from a flame causing alcohol fuel to expand in a pressure vessel (the stove). That pressurised fuel escapes through holes and ignites, keeping the flame (and the whole cycle) going.

I generally have one of these in my camping kit as a backup stove. They are small and light and very practical.

Right now my lawyer (Mister Lionel Hutz, AKA Miguel Sánchez, AKA Dr. Nguyen Van Falk) will want me to say do not try this at home. Building and using the stove involves some risk(s). Some of those risks are obvious, such as sharp edges, burny flames, others less so like carbon monoxide poisoning, death, etc,.

There are several versions of penny stoves out there already however, I have my own method (explained below) that takes some of the difficulty out of the process which may be of academic interest to stove heads and ultralight backpackers.

All you need to construct your penny stove
The components and tools
1. Two aluminium drinks cans (one FULL, one empty). These will become the stove body.
2. One penny coin. This will become the essential safety valve.
3. Two drills (one 1.5mm the other 6mm), and a hand drill.
4. An ink marker for marking on the cans.
5. Household scissors for cutting the cans.
6. Very fine sandpaper for buffing the paint off the cans. (optional)

Note there is no ruler, everything was 'eyeballed'. The cans must be identical to ensure a good fit.

Marking a parallel edge
Marking a parallel line approx 40mm (1 1/2 inches) on the empty can.
After marking a line parallel to the workbench I cut the can with scissors. It cuts very easily as the can is extremely thin, and it was important for me to cut a perfectly parallel line as this will be the edge that my stove sits on. This is the first difference in my technique, I cut with scissors and not a craft knife. It is way easier.

Cut with scissors
A nice clean cut
Next I drilled out the pressure vent hole using first the smaller drill followed by the larger drill.

Drilling the pressure vent
I could have used a power drill/driver, but a hand drill is up to this job.
I had to drill the pressure vent hole before this next step where I press the full can (bottom first) into the cut can. If you don't drill this hole first, trapped air will prevent you from pushing the cans together permanently and both halves will soon part company.

Pressing the base
Gently pressed to fit
I pressed the bottom of the full can into the cut can approximately 12mm (1/2 inch). This is another difference from the 'usual technique'. Usually you cut the bottom off two cans and press them together, cut edge to cut edge.

Keeping the can full means that it has enough rigidity to stand this process and it stretches the cut can by acting as a form to make a good enough seal without glue. No need for slits or shims if you are not trying to press one cut can into another cut can and the added bonus of less chance of cut fingers.

I then emptied the full can, drank it (mmmm, burp!) and cut it down to the edge with the scissors.

Based Pressed and cut
Both cans cut and pressed together, bashed can quality control failure!
Then I marked out the burner and drilled out the jet burner holes with the smaller drill.

Starting to drill
Look carefully to see the marks
After a short time the drilling is finished and the stove is essentially complete. It is a good idea to buff off the paint with some fine sandpaper.

Drilling Complete
Note that the drilling does not have to be precise
The total build time was lest than 10 minutes.

"WTF is Irn Bru anyway?"

Irn Bru is Scotland's "Other national drink" after whisky of course! It has been used for decades as a traditional folk remedy if you drank too much whisky on the night before. It tastes of raw magic, and is made to a ancient druidic recipe, that is still kept secret by the Barr family who make the draught in nearby Cumbernauld.

Continue to part two