I was reading the "taig users" yahoo group recently where I came across a post in which someone had purchased a taig mill and lathe for the purpose of building a fire piston. Having the idea that this was some fancy engine, I quickly did a google search to find one. To my surprise this was not an engine but an instrument used to generate lit tinder for use out in the wild...and what an amazing method it used. It is simply a closed ended cylinder with tight fitting piston with tinder at the end of the piston. When the piston is rammed quickly into the cylinder, the quick compression of the air generates enough heat to light the tinder!
Here is a quick video of it working with the pictures included:
A good googling on the topic found quite a few "make your own fire piston" instructions, but all using easy to come-by materials. So using the measurements from these I set about making my own. The length is 4.25" and the bore is 10mm (nothing like mixed measurements!). This was only a quick project, probably 3-4 hours machining but I struggled to get a good bore due to the fact I didn`t have a long enough reamer or boring bar. Still, a standard 10mm drill has worked with an o-ring to seal it well. This was all made up as I went along so there are a few mistakes and it hasn`t been polished!
The head of the piston was originally brass. You will see that although this fire piston works, making the bore 10mm is a little wide and so the force needed to compress the piston is quite high. A little too high for compressing it in your hands (I have actually done it but it hurt my palm!!) It is much easier to hold the cylinder and slam it down on something hard. I wanted to put a little cap on it anyway to hold some tinder, so I`ve made the cap out of steel. I guess it could be replaced as well. All this being said, if I was to make it again, I`d make the bore narrower so that less force is needed to be applied to compress the cylinder - so a steel cap would not be needed.
1/8" hole in the bottom; this is where the tinder sits. The little square is the piece of char cotton I`ll be using as tinder.
The hole filled with char cotton.
Well, I should have cleaned it up a bit before taking this photo but this is the end cap. This provides a solid top, a pocket to store some char cloth and an extra washer to be used on the piston if needed. I`d make this bigger if I did it again.
The char cloth I made using a 100% cotton bed sheet, cut into four 3" square sheets and put into a metal travel sweat tin. The tin had a small hole in the top (1mm) and was placed on a camping stove for 20 mins until all the smoke coming through the top had stopped, removed from the heat and sealed the hole. Lots of info on the net regarding char cloth. I was told that using char cloth is a "must" while testing a fire piston but I believe other tinders will work in it.
Char cloth lit and burning away...!
