Intro: Illustrated & Detailed Guide to Making a Fire Piston
In this instructable I will attempt to show you how to make a fire piston using relatively common materials found at your local hardware store. It took me a few attempts to get it working right so hopefully this instructable will help you benefit from what I've learned. The cost is under $20 per piston though some of the suplies like brass rod only come in 4ft sections so I'm dividing the cost down for each individual unit.
What's a fire piston anyway?
A fire piston is an amazing little tool that's been around for hundreds of years, unfortunately due to the invention of the common match its popularity diminished and it almost dissapeared. It is a piston and cylinder that works like a diesel engine using compression to cause a piece of tinder to heat up rapidly and turn into a coal. Wikipedia explains it better than I do so if you're really interested just click here for the full history.
The most important part about getting one of these working seems to be the char cloth or char string which is used as the tinder, don't be fooled by other videos online its almost impossible to light just regular balls of rolled up tissue paper. Charcloth is a cotton based material that is heated in an oxygen deprived container until certain gases etc are released afterwhich the remaining material turns to an ember really easily. Another characteristic of char cloth is that the ember grows when it is blown on (so wind actually helps you!)
Making a fire piston without having char cloth will make you go crazy, chances are you'll have a working piston but won't know it because your using the wrong tinder. Make char cloth first!!!
5" or more of 1/4" brass rod
4" 1/8th Threaded brass pipe nipple
1/8 Threaded brass cap
1/4" OD 1/8" ID 1/16 Cross section rubber o-rings aka -006 size
2 part liquid epoxy (Jb Weld, Cold Weld etc)
Wooden cabinet knob (or you can make your own)
Wooden Broom Handle or suitable wood for turning*
Cotton T-Shirt (Optional for making char cloth)
Tin can that seals (Optional for making char cloth)
Drill Press & Drill Bits
*Not all the tools/materials are necessary just to get a working piston. Instead of using a lathe you could file the o-ring groove by hand for example. The wooden sleeve made from the broom handle is optional as its purely cosmetic.
**All the slides were made with Google Sketchup, playing around with the styles gave it the illustrated look and it reminded me of a kids book so I ran with it ;)
Step 1: Cut Raw Brass Rod
Cut approximately 5" of the brass rod using a hacksaw. We're cutting it a little longer than we need, the excess can be trimmed off when we are fitting the handle.
Step 2: O-ring Groove on Piston
On a lathe use a triangle file to reduce the shaft diameter to 0.175" The tapered part should be at roughly a 45 degree angle. Next file one side of the piston head flat so that you can center punch it to
drill a hole. Make sure you don't do it too close to the end of the piston!!
Note: It is important that the o-ring grove is tapered at 45 degrees on the one side, as the piston is forced down in the cylinder the o-ring rides up a little and is expanded by the taper thus providing a tighter seal. If this angle is too low the o-ring will slide up the shaft completely which is no good, I found 45 degrees was about right.
Step 3: Pilot Hole for Tinder
Start off using a small bit to drill a pilot hole, this will make drilling the larger hole quite a bit easier. Make sure the hole is centered and perpendicular to the length of the piston.
Step 4: Full Sized Tinder Hole
With the pilot hole drilled you can now proceed to drill the large hole. A number 31 bit seems to be about the right size. Notice how there is still a bit of material left between the hole and the piston end. If you don't leave a little room the drillbit could slip out!
Step 5: Tinder Slit
Using a file cut a slit through the end of the piston to meet the hole we drilled. If you had too much excess material between the hole and the piston end from the previous step you can file it down or cut it off. * It's also a good idea to round over the bottom edge of the piston as well as any sharp points & corners.
Step 6: Starting the Cylinder
The threads on brass nipple piping is tapered so you won't be able to screw it on the whole way. Its a good idea to thread it on and off a few times with your fingers to get rid of any burrs left from manufacturing.
Note: I don't know what it is about brass nipples but the measurements are strange, they are listed as 1/8th but the inner diameter is closer to 1/4" (0.277 by my measurements) the wall thickness doesn't seem to be 1/8th either. Nothing about 1/8th brass nipple seems to actually be 1/8th. If anyone knows please enlighten me ;)
Step 7: Epoxying the Brass Cap
Fill the cap up all the way with the expoxy. I suggest "JB Weld" or "Cold Weld" not the putty variety. Thread the cap on as far as you can. Leave sitting upright to dry overnight, this will ensure the bottom of the cylinder remains flat.
Note: I've heard of other people using the putty but they had to use the un-cut end of their piston to flatten it out after, I don't know if the putty makes as good of a seal or not so I'd stick with the liquid stuff.
Step 8: Flaring the Cylinder
Using a large tapered punch, flare out the end of the brass nipple. If you do not have a punch you can dremel or file the bore larger instead, just take care not to mar the cylinder further down while doing it.
Note: It is very important that you have a smooth flared end to the cylinder so you can get the piston started. If its rough it will scar your o-rings and you'll have to change them often.
Step 9: Mark the Piston Depth
Insert the piston all the way into the cylinder and mark the depth on the side of the piston. This will allow you to determine how far the piston will sit inside the handle.
Note: Some other tutorials will say to leave a gap at the bottom of the piston, this isn't necessary with the way the tinder slot is made on this one. Infact leaving room will only reduce the compression and possibly prevent the tinder from igniting at all. I found as long as your seal is good you shouldn't "bottom out" when compressing the cylinder or not very hard at least if you do.
Step 10: Piston Handle
Its up to you whether or not to turn the handle first or at the same time as the cylinder sleeve. A good handle has a slight curve to it so it doesn't hurt your hand :)
Note: A simple solution is to just pick up some wooden cabinet knobs to use as a handle. You'll probably have to drill the hole in them bigger though but that is easy.
Step 11: Piston Sleeve/Body
from the other side, drill another hole part way that will accept the cap.
- Shown here the sleeve has decorative grooves cut into the wood, this is just for looks and nothing to do with functionality.
Step 12: Plug the Bottom
You'll need to fashion a plug to fill the hole on the bottom and hide the brass cap from sight. Just make sure that you remember to insert the brass tube before you glue it all in place!
Step 13: Finished!
You should now have a finished fire piston, now all you need to do is make some char cloth and you can try it out!
Step 14: Easy O-Ring Installation Trick
Since you'll probably have left over brass rod stock why not make a little jig for installing o-rings. Simply taper a 1" long piece of rod down but not quite to a point, then butt it up against the piston and pop the o-ring on!
Step 15: Tips for Getting Coals
1) Make sure your fingers are dry, if the char cloth gets contaminated it won't light well (especially if your fingers have left over vaseline from lubing the o-ring).
2) Sometimes pausing slightly after you compress the piston will help allow more heat to transfer to the char string or cloth.
3) Make sure you're getting enough compression, the plunger should be fairly hard to press for the last 1/3 and after released should pop out about 2/3's. If it is not then try re-lubing the o-ring with vaseline or chapstick.
4) If you don't get a coal after a few attempts try a different piece of tinder.
5) After a misfire it helps to blow down the cylinder, this helps to get new air in the cylinder and purge it of the spent gases.
NEW 6) I forgot this one when I was doing up the slides, if you leave a little sticking out the end of the piston (ie out the slit instead of the side holes) I've found this often lights easier.
Step 16: Making Char Cloth
Charcloth is relatively easy to make and a crucial ingredient to using your fire piston. Simply take an old cotton shirt, cut it up into squares, then place into a sealed metal can. Poke a small hole in the top of the can with a nail, then roast over top of a fire until the smoke stops coming out of the hole. Remove from the fire and put the nail back in to seal the can. Let it cool, when you open it the cloth should be black but not brittle. Use a white shirt the first time because its easier to see when it is charred. Also, don't be alarmed if the smoke ignites while making this, that is normal ;)