Update 2: The physical principles governing the dynamic/transient action of a fire piston are a bit more involved than a simple application of Boyle's Law in steady state (i.e., PV=nRT). Here are some articles that describe the physics of the fire pistion in more detail. Perhaps these will answer a few questions and settle some debates. I am not a co-author of any of these articles.
How Hot Can a Fire Piston Get: drive.google.c...
Physics of the Fire Piston: drive.google.c...
The Fire Syringe: drive.google.c...
History of the Fire Piston: drive.google.c...
Update 1: I had such good success with the fire piston showcased in this video, that I decided to make another with some remaining spare parts. It was a magnificent failure - at first. I could not get an ignition to save me. I tried everything: swapping O-rings, new O-rings, more lube, less lube, different lube, press harder (even whacked the piston with a rubber mallet a few times), polish the cylinder more, fresh char cloth, etc. Nothing worked. Aargh!!!!! After exhausting all the logical possibilities, I decided that I’d try one last thing that risked ruining my new piston completely.
I had gotten a really tight seal on both of my O-rings. As a last ditch effort, I decided to lightly file both of the O-ring grooves just a bit more to loosen up the seals. That did the trick! Bonsai! I got an ember on the very next try and several more after that. I’m not sure exactly why that worked. It may be that I now get more piston speed during compression. It may be that my compression was just too high to start with - it does seem now that my piston goes further into the cylinder when I whack it. Perhaps there is an optimum compression that needs to be dialed in? I just don’t know. Regardless, if you start with very tight seals and fail to achieve ignition, loosening up the O-rings a bit (just a little!) may do the trick. Always go slow and test.
Now I have two awesome fire pistons. Woo Hoo!
Materials List:
5” length of 1/2” copper tubing (Type M) - deburr and chamfer inside edges
One 1/2” copper end cap - solder or epoxy onto one end of the copper tube
#8 O-rings (9/16” OD, 3/8” ID)
1/2” wooden dowel rod (Oak, Poplar, etc.)
Wooden or plastic knob of some sort.
Wood Glue - to glue knob onto the piston rod
Super Glue - to harden and seal the piston tip
Wipe on Polyurethane (optional) - to protect the piston
Project Inspirations:
JonTheWoodWorker: • Making and Using a Fir...
NativeRobin: • Making a Fire Piston a...
For reference, this fire piston project took me about 3.5 hours to complete, spread over 4 evenings. This does not include the super glue or polyurethane drying times, nor does it include the time needed to shoot the final firemaking scene.
Overall I have mixed feelings about fire pistons. Mostly I don’t much care for them. This one turned out very well, but ensuring a good seal and sufficient compression is tricky. I’d say most of my fire pistons work about 50% of the time. O-rings wear out, lubricant accumulates in the cylinder base, etc. I just wouldn’t want to rely on a fire piston when the chips are down. Nevertheless, this was a fun cold weather project to pursue. I hope you had fun watching.
One more thing… I suggest wiping off the lubricant when you aren’t actively using your fire piston. That will help preserve the O-rings, especially if they are natural rubber and you are using lubricants with petroleum distillates. As I mentioned in the video, Nitrile O-rings will be better, but they are a bit more expensive and harder to find.
Ahi! Sua! Qul!
4 окт 2024
