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
Step 2: O-ring Groove On Piston
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
Step 4: Full Sized Tinder Hole
Step 5: Tinder Slit
Step 6: Starting The Cylinder
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
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
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
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
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
Step 13: Finished!
Step 14: Easy O-Ring Installation Trick
Step 15: Tips For Getting Coals
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.