Home made fire pistons: Leaking wooden piston rods

[Galemys]

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

 

[Ogri the trog]

Hi Galemys,
I'm sure I've seen a video somewhere on the web of a largish piston with a leather washer sealing the tinder cavity. I haven't tried too seriously with natural materials for pistons (baring Jeff Wagners examples) so I can't help from direct experience.

ATB

Ogri the trog

 

[Jeff Wagner]

Tom - You are on the right track. Porosity is a big problem when using wood. I know a fellow who managed to seal a porous wood using pitch by the way.

 

[Galemys]

The glue certainly worked to make both piston rods I was making airtight. In fact the compression I finally got was so good that I blew the end pieces out of both the 7 and 8 mm (inner diameter) pipes... One was soldered, the other glued in place to close the ends of the tubes. The smaller one at least had the decency to produce a coal while I was trashing it

I consider switching to glueing the piece of pipe into a prebored hole in hardwood to avoid the difficulties I have with closing the end of the pipes.

Jeff,
thanx again for sharing your knowledge, I will try out the pine pitch.
Have you ever had success with anything other than cocobolo wood? Are there North american woods that could produce working fire pistons without anti-porosity treatment?

If I get these two pistons to work I am going to try making piston rods with wound gaskets.
My god, that sounds like I have actually set myself a goal for 2007...

Tom

 

[Jeff Wagner]

I have used Bloodwood, Ebony, Granadillo, Lignum Vitae, Desert Ironwood and Bubinga with good results. As for native species - I have been meaning to give hickory and ironwood ( American Hornbeam ) a try, but to be honest, I have been so busy actually making pistons over that past couple of years that I've had very little time for experimentation. The critical issue is the pore structure of the wood as opposed to its hardness. Purple Heart for example is a hard and dense wood but it has open pores and leaks like a sieve.

 

[Galemys]

As for native species - I have been meaning to give hickory and ironwood ( American Hornbeam ) a try.

We don't have hickory over here but a species of Hornbeam (Carpinus) is native to this side of the pond. I will source a piece of that to try out, it is not an uncommon tree to be found.
And now for some trivia: the word 'Hornbeam' is derived from horn & 'beam' an old word for tree ('boom' in Dutch).

Tom

 

[T1tch]

Hi everybody - After lurking for a while I've finaly got a question that I can't find already answered, so here I am.

I've had a bit of a go at constructing a piston from beach, however I'm erring towards believing that it may be to porus

So now I'm toying with the idea of using Yew - not knowing much about wood, is this is this worth a try? Has anyone tried using Yew

 

[Galemys]

Hi everybody - After lurking for a while I've finaly got a question that I can't find already answered, so here I am.

I've had a bit of a go at constructing a piston from beach, however I'm erring towards believing that it may be to porus

So now I'm toying with the idea of using Yew - not knowing much about wood, is this is this worth a try? Has anyone tried using Yew

Hi T1tch and welcome to the forum,

I still haven´t managed to make a fire piston totally out of wood but I suspect yew will be too porous as well. I started out making them from copper plumbing pipes but the last ones I made with a piece of brass tube glued into a drilled hole in a piece of hardwood. This was tropical hardwood of unknown kind, very hard and heavy but still too porous to contain the compressed air. I make them airtight with a few drops of superglue on the bottom of the tube and on the end of the piston rod. If I were you I would first try making a fire piston out of brass or copper tube and if that works step over to wood.
If you have anymore questions, just shout.

Here´s one I made in hardwood with brass tubing:
http://s162.photobucket.com/albums/t258/galemys/?action=view&current=P1010935.jpg

Cheers,

Tom

PS why don´t you introduce yourself to the rest of the forum in the introduction and welcomes section?

 

[T1tch]

Cheers Tom - that's saved me some time: this yew is so hard I'd have been gutted if I'd spent hours polishing the bore only to find it leaked!
After looking at your picture I think that is a good way to go - I shied away from the idea of using metals as I thought it may detract from the appearance of the finished article, however if anything it adds to it.

As for introductions - I'll pop along there shortly

Thanks again for the advice

Cheers

Mark

 

[Galemys]

No thank's, just don't forget to show us your result!

Cheers,

Tom