Fire Pistons

[Ogri the trog]

Hi Jeff, thanks for taking an interest,

Materials - I found that I couldn't drill a hole of the necessary surface finish, even in plastic. So I improvised, drilled a larger diameter hole and used a few inches of commercial airline inside the blind hole, rigid body and a polished bore.
I turned a piece of aluminium as the piston, with a waisted section for an O-ring seal and an open cup at the business end.
The compression was OK but not stunning so I fitted a cut down pneumatic blank inside the bore to give it a flat bottom. This was the state that gave some the embers, but, as mentioned - not repeatably. The most recent modification, is a thin plastic spacer (about 1/16th inch) to give a bit of clear "head room" for the tinder, I'm using char cloth by the way.

When I get it repeatable, I intend to start replacing items one-by-one, hopefully maintaining the performance, until I get an all natural example.

What are your thoughts?

Cheers

Ogri the trog

 

[jim_w]

Yeah, I'd appreciate a few tips here too. I've got a reasonably air-tight prototype, but I can't for the life of me get it to work. I'm using a bit of plumber's copper pipe with an end cap and a wooden piston with two rubber O-rings, greasing it with lard and using odds and ends as tinder. I suppose I should be using charcloth as tinder, but I'm too idle to make any. ;-P

 

[Jeff Wagner]

Problem solving is half the fun. Firstly, I will need to know if the pistons are not performing due to loss of compression or some other factor. If the pistons can be made to fully bottom-out without too much effort, they are leaking. It will be necessary to determine where the leakage is occuring. Commercial tubing may have a smooth bore surface, however there is no guarantee that the bore is round. I would evaluate for ovality.

 

[jim_w]

Well, even if my tube is perfectly round, I can assure you my piston isn't! I had hoped that the squishyness (technical term ) of the O-ring would make up for that - perhaps not. Let me make a short list of the things that I'm aware of having to be perfect:

- the fit of the piston (roundness and size)
- the air-tightness of the tube (test with water)
- the quality of the tinder (one site said ordinary dry paper would do; others say stuff like charcloth)

I'm sure there are more that I'm missing...

 

[Jeff Wagner]

There are four places where leakage can occur. If your cylinder and piston are made of non-porous materials, you have reduced that to two places. Its either leaking over the o ring ( blow-by between the cylinder wall and o ring ) or under the o ring ( between the O ring and piston groove ). An O ring that is too squishy ( technical fire piston term... may deform to allow blow-by as the pressure increases.

 

[Ogri the trog]

Yeah, I'd appreciate a few tips here too. I suppose I should be using charcloth as tinder, but I'm too idle to make any. ;-P

Jim,
Before Jeff laughs out loud at you, go make some charcloth and show a bit of commitment to heeding his advice. I might also be overstepping the mark to suggest that anything over 10mm in diameter is a bit ambitious for a hand operated fire piston.

Jeff,
I'm using an O-ring that is available through my work and the hardness (Shore number) could be allowing blow-by and hence be the reason why I can't get repeatability. I might try widening the groove for a second seal or maybe try making a square section rubber seal that is a tighter fit. If there is any machining to do, it'll have to wait till I get back to work in the middle of next week. For now, I'll persevere with it as is.

Continued thanks for your interest.

Ogri the trog

 

[jim_w]

Jim,
Before Jeff laughs out loud at you, go make some charcloth and show a bit of commitment to heeding his advice. I might also be overstepping the mark to suggest that anything over 10mm in diameter is a bit ambitious for a hand operated fire piston.

Ogri the trog

Yeah, next time I get a chance I will, but living in a city makes it rather difficult to light an open fire whenever I want, and sharing a house means I'm too afraid to do it in the oven!

Have you seen "fire dust" from "light my fire"? It's scrapings from some kind of pine tree, and burns really well. Would some of this do as tinder? How about the head of a match (just to test, obviously! ) ?

10mm eh? That's... (goes to google) about 0.4 inches. Aaaah. I'll try a smaller tube if I can find one. I'd naively thought that a bigger tube would be easier!

Jeff:

Well, my O-rings are glued in place, so I doubt it's leaking under them - that only leaves over. I'll fill the thing up with water and see what happens. To be honest, I think I'm probably going to end up buying one! I'm really impressed by anyone who can make one of these out of natural materials, but I find it slightly odd that it's not possible to buy cheap plastic versions. Not enough demand? Or maybe the sort of person who wants a firepiston also wants it wooden.

Thanks both of you for all your help, and good luck Ogri!

 

[Ogri the trog]

Jim,
Have you seen the "Alternative Charcloth Tutorial"? Making char-cloth in a piece of copper pipe, it still gives off plenty of smoke and smell, but I recon you could do it in a flower pot using a blow torch! There's even a guy selling charcloth on Ebay!
The Maya dust I've tried is not much good unless you can get it really hot with a spark, I've tried without success in my fire piston, though Jeff has recommended wood punk.
"I'd naively thought that a bigger tube would be easier!" I think that a smaller diameter is more efficient - just think of the volume of air that you are trying to compress. Its a Force X Area thing, and your arms are only so strong, reduce the area and your input force becomes more effective.
I'm not sure about glueing the O-rings into place either - allowing them to deform under pressure to fill any voids might be better rather than making them rigid and inflexible with glue.

Sorry about the rant earlier on, when you said you were too idle, I took it as "Failing to prepare - preparing to fail" and a slight on Jeff's well intentioned advice, rather than thinking about the constraints of your circumstances.

ATB

Ogri the trog

 

[Jeff Wagner]

Size - 10mm will work, but 9mm will work better.

Charcloth - Personally, I never use it, but it is an option if that is all that is available to you. A shoe polish tin will make all the charcloth you will need and in a stiff breeze the neighbors will not know where that stink is coming from...

Pine pitch / fat wood - Great stuff when igninted by flame but of no use in a fire piston

Mass produced, cheap, plastic fire pistons...... Good Heavens !!

Your water testing is on the right path. This is a useful diagnstic method.

When all is working well your piston should be stopped by a cushion of compressed air and rebound at a point about 10mm short of full insertion. If you can achive this, you can ignite rotten wood, mullein pith and amadou.

 

[Ogri the trog]

Thanks again Jeff,
I'll collect some tinder while out today, rotten wood should be no problem. Can't say that I've seen any Mullein, but that wont stop my trying with similar UK varieties. Amadou is my holy grail for the moment, try as I might I can't find any locally - butI'll get around that in due time.

Cheers

Ogri the trog

 

[Jeff Wagner]

Good luck on your efforts. Since you have birch its curious that you dont have tinder fungus ( inonotus ) however there must must be other native alternatives. I've heard that king alfed cakes and crampballs light up in the piston but I have not had an opporunity to try for myself.

 

[Ogri the trog]

Thanks for your good wishes Jeff,
Once the children are back in school tomorrow I can spend a bit more time practicing, if theres any news, I'll post it here

Ogri the trog

 

[jim_w]

<sounds of brain-wheels turning slowly>

Thanks jeff and og - you've both been most helpful

p.s. og: I didn't even notice the rant; I assumed you were joking too! A lot of social stuff just goes right over my head - I'm a little autistic I think

 

[Jeff Wagner]

Here's a photo of a horn piston for your ogling enjoyment. The piston top has a hollow cavity for the storage of lubricant.

 

[Ogri the trog]

Hmmmm,
.....a minor redesign is on the cards I think. I checked mine with water and it holds with my weight on it but I have a feeling that I'm getting blow by under the O-ring in air. My thoughts are to remake (or rework) the piston with a larger diameter waisted section for the O-ring.
I found some rotten wood which I have dried as tinder but its not staying in the cup too well. Mullein and amadou are remaining elusive but I have to say that this learnning curve is getting exciting.
Is there any specific way of preparing the fungus other than drying it out?

Ogri the trog

 

[Jeff Wagner]

I would retry the water test at various depths. What holds at the top may leak further down due to variations in cylinder bore diameter.

The natural tinders I use, Inonotus, milkweed, mullein, punk, etc. require no special treatment other than drying.

 

[Ogri the trog]

I tried the test with smaller amounts of water but with the piston "bounce" on the air above the water it became difficult to determine whether it was leaking or not.
To my mind the only other thing that would be stopping the formation of an ember is that the tinder is contacting the flat bottom of the bore and robbing the precious heat from where it is needed, a bit like stubbing out a cigarette.
...thats assuming of course that there are no dark secrets that I am, as yet unaware of



....Of course there are secrets, without them I wouldn't be hanging on to Jeffs every word.

I'm striking the piston into the bore with a forcefull hand slap with the bore rested on a solid surface, then pulling the piston out as soon as I can. There may be other methods, such as holding the piston and then jerking it down with bodyweight. The demonstration videos of folk "clapping" them between their hands is a way off pipe dream for the time being.

I'm off to peruse Jeffs site again.

Ogri the trog

 

[Jeff Wagner]

Well, it certainly sounds like you have good compression. Hold it up to the monitor so I can have a look....

Seriously, can you send a photo? Perhaps I can see what the problem is.

When you insert the dry piston, does it exhibit the same bouce-back as with water? Tinder contact with the bottom should make no difference.

 

[Jeff Wagner]

[The demonstration videos of folk "clapping" them between their hands is a way off pipe dream for the time being.

That so called "clapping" ignition method was developed out of shear necessity. I probably hold the world's record for most tinder ignitions by fire piston. As a result I acquired a very sore palm. I came up with this "crunch" method to reduce the damage to my poor hand. It works so well however that its become my standard technique for lighting the pistons. In an unsupported palm strike, the cylinder is able to move away, thereby absorbing some of the force. The crunch method drives both piston and cylinder together simultaneously for increased effectivness.

 

[Ogri the trog]

Well, it certainly sounds like you have good compression. Hold it up to the monitor so I can have a look....

Seriously, can you send a photo? Perhaps I can see what the problem is.

When you insert the dry piston, does it exhibit the same bouce-back as with water? Tinder contact with the bottom should make no difference.

Ermm,
Don't quite know how to put this..... of the cameras we have here, the only one I can download from is currently 100 miles away .
I'll try a verbal image.
8mm diameter piston with a full stroke of about 100mm. End cup is approx 6mm diameter and 3mm deep, the O-ring groove is 5mm back from the tip and is 2.5mm wide. O-ring is about 1.8mm in section so there is a small amount of free longitudinal movement of the seal.
Bore is flat bottomed with a 2mm buffer at the bottom for head space but has suffered some damage (from early attempts) near the mouth of the cylinder, so it rebounds to about the 60mm point, allowing 20mm for damage it is starting to look as though ther is a small problemette.
I can hold the piston at the bottom of its travell without too much effort......
..... and now I'l thinking........
I'm using a liner of industrial air hose (for smoothness and concentricity of bore) inside a plastic body (for rigidity). When assembling the body, I used epoxy glue - of which a lot was forced back along the inner tube...
...what I'm thinking is that I might be loosing compression between the two layers which might have been masked by the water being so much more dense. I think I might have to replace the inner hose and pay more attention to sealing the bottom end of the cylinder.

What with my earlier post about a rehash of the piston, this is sounding like a "back to ye drawing board" moment, though it will be later in the week before I can get near any materials and machinery.
Rest assured that when I get a reliable working model I'll post a picture of it somehow, even if I have to continue using charcloth!

Jeff thanks for being the "ear in the ether" it has helped a lot to bounce my ideas and thoughts off you.

Ogri the trog

PS I've managed 2 embers this evening, but when trying for a third - nothing!