I was testing a new homemade fire piston made out of a piece of metal pipe with a wooden piston rod when I stumbled upon a strange observation.
I already knew that you have to use a wood with a high density for the piston rod in order to get good air compression. What I hadn't expected was that even piston rods made out of relative heavy woods as oak & beech were still too porous. I guess I was just lucky with the choice of wood I used for my first 2 (working) fire pistons.
The result of using a porous wood is that the air that you are trying to compress in the tube escapes straight through the wood. At first I was puzzled at where the leakage was occurring but then I tried the piston again, filled with some water. If you have a decent working fire piston, the piston rod can only be pushed in for a short distance because water can not be compressed. With my 'leaky' wooden piston rods I could force the rods slowly into the tube while the water was 'sweating' out of the wood, most of it following the grain and dripping out at the end of the rod.
So for anyone out there trying to make their own fire piston:
use a very dense tropical hardwood or try to treat your wood in a way that makes it more airtight. I have tried saturating the wood with oil but that didn't work, I'm gonna try using varnish or glue to treat the working (tinder cavity) end of the piston rod to see if that helps.
So I'm left with a few questions:
Are there any other, more bushcrafty, methods that will work to treat a porous wood and make it more airtight? Pine pitch perhaps?
Are there non-tropical woods (preferably growing in Europe) dense enough to use directly without treating?
Tom
I already knew that you have to use a wood with a high density for the piston rod in order to get good air compression. What I hadn't expected was that even piston rods made out of relative heavy woods as oak & beech were still too porous. I guess I was just lucky with the choice of wood I used for my first 2 (working) fire pistons.
The result of using a porous wood is that the air that you are trying to compress in the tube escapes straight through the wood. At first I was puzzled at where the leakage was occurring but then I tried the piston again, filled with some water. If you have a decent working fire piston, the piston rod can only be pushed in for a short distance because water can not be compressed. With my 'leaky' wooden piston rods I could force the rods slowly into the tube while the water was 'sweating' out of the wood, most of it following the grain and dripping out at the end of the rod.
So for anyone out there trying to make their own fire piston:
use a very dense tropical hardwood or try to treat your wood in a way that makes it more airtight. I have tried saturating the wood with oil but that didn't work, I'm gonna try using varnish or glue to treat the working (tinder cavity) end of the piston rod to see if that helps.
So I'm left with a few questions:
Are there any other, more bushcrafty, methods that will work to treat a porous wood and make it more airtight? Pine pitch perhaps?
Are there non-tropical woods (preferably growing in Europe) dense enough to use directly without treating?
Tom