Creating fire by different techniques is fundemental to bushcraft. For years I have been intrigued by the fire piston, but considered the skill to make one was beyond me.

I then watched the video on this bushcraft site of a piston being carved out of wood with a parang. An awesome example of skill using a variety of knife techniques. I decided to make one and read numerous articles on the net. I was keen to keep costs low and use easily obtainable materials.

If you are not familiar with the concept watch pistons been used on youtube.

Here is a description of my sucessful prototype, it is a bit crude in appearance but works well.

Material

Pvc pipe from plumbing supplies $5/m. Smallest diameter I could find

17.5mm internal diameter . Larger than I was after.

O ring with an exterior diameter equal to or slightly less the the interior of pipe. 10 O Rings for $2.50

Dense wood for piston and end plug

I used manuka for the piston and hickory for the end plug.

( you can buy PVC end plugs but the ones I found were unsuitable because they created an unuseable cavity in the end)

5 minute epoxy. I was surprised to find that this works O.K on PVC

Construction

cut my tube to a length of around 14cm

I carefully carved an end plug and sanded for a very tight fit. This was hammered in and held in place with epoxy. Plug around 1cm in length Carve piston, leaving a substantial handle(i 'd make it bigger next time) The piston diameter is just smaller than pipe diameter. In operation the piston reaches the end of the barrel just as the handle hit the tube . This determines the length if the piston. Carve a notch near the end( 4mm from end in my case). This is an exacting process, I used a hacksaw. knife and sand paper. Make the notch smaller than require. Then carefully sand. Since I did not take any photos at the time I have pinched some picture from the net. This is slow job. Sand check, sand check. You want the O ring to just fit the barrel, but it must moved freely. If the sides and base of the notch are smooth this should be an air tight seal. I have included a photo a slightly different technique. This is to fill the notch with epoxy put on the O ring wipe off any excess glue,leave piston in the bore until dry. I tried both techniques,with equal success. The epoxy forms a uniform and airtight base, but you need to make sure that things are not too tight in the bore. In operation the pressures are quite large . Most woods are porous and air can be force into them significantly reducing the compression ratio and hence the chance of combustion.It is therefore necessary to cover all the working end of the piston and front face of the end cap with epoxy to stop air being forced into the wood. This is important. Finally a hole in the end needs to be carved for the char cloth. This needs to big enough to do the job but not large enough to signifiantly increase the volume.

I used vaseline as a lubricant,this creates the air tight seal and reduces the friction considerably.

In future i'd like to make a more traditional piston without the O ring, instead using a cotton washer system,it looks easy in theory but sure its a tricky business.

All the internet sites I have found are overseas and naturally their resources are different. http://wildwoodsurvival.com/survival/fire/firepiston/rbmodelt/index...