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!!!

Materials
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)

Tools
Drill Press & Drill Bits
Lathe*
Triangle File
Hacksaw

*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

Cut a section of wooden broom handle and drill it out with a bit just bigger than the brass nipple. Then,
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 ;)

Comments

[LLuE88.]

What is the actual inside diameter of the 1/8" brass pipe? reason for the question is the i.d. of 1/8" brass pipe varies lately, it used to be very close to 0.254", now it's likely closer to 0.270" which really stretches the viability of an o-ring to seal the rod against the cylinder wall. It might be best to buy a brass tube of 0.500" O.D. x 0.250" , then reduce the end for threads - then cut threads for the cap. then with very fine sand paper reduce the rod by about 0.003" clearance. thanks

[jphphotography]

I'm really not sure what to tell you, since the ID isn't the spec'd dimension you sort of have to take what you get or if possible just bring a micrometer with you. The whole idea was to use easily sourced off the shelf parts, I'm sure with the proper tools you could just machine all the parts yourself using rod stock but that was out of the scope of this instructable. Cutting threads etc seems a bit advanced, also the regular brass tubing I had access to was very thin walled (hobby tubing) so you couldn't thread any caps onto it, these were the best option I could find. To accommodate for the variability in the ID you could also try buying an o-ring variety pack and just finding one that works, that's what I did and then found the size that worked and used that on the rest that I built and they all worked fine, it could be that the box of brass pipe I got was all similarly spec'd. Sorry I don't have a better answer for you.

[LLuE88.]

FROM, LLuE88



Most vendors do not show nominal pipe i.d. , but a specific designer likely needs more info. Earlier there was a site that also spec'd the 1/8" brass pipe nipple for a fire piston with no indication of required I.D., at that time I bought a 6" brass nipple from Home Depot with the 0.254" I.D. "at one end only" the other end was 0.275", change at about 2.5" from end, talking about being upset at their quality control, they had no explanation for it {there were six more with exactly the same issue on the hangers}. I suppose ignorance is bliss, but a serious project person must research needed details or some how work around these sorts of problems. General use doesn't need i.d. or wall thickness
Below find link to one of quit a few that do give the required info.

http://www.onlinemetals.com/

With the i.d. knowledge you can easily make a plug from the same rod used for the piston itself by cutting about 1/4" long, at the center of outside end put a deep center punch into it, then drive it into the pipe or tube of about 0.25 or 0.254" i.d. about 1/64" past flush from bottom end of cylinder for a solid closure. thanks

[Shootin Wizard]

what size is a 31 dill bit

[Bryan B]

A wire size #31 drill bit is 0.1200 inches in diameter, I used a 1/8 inch bit which is 0.1250 inches (the difference is about the thickness of an average human hair) to make mine entirely on a lathe (before I read this instructable).

[jphphotography]

@ Bryan Nice looking piston! Does the narrow end hurt your hand though when striking it?

@Shootin Wizard
http://en.wikipedia.org/wiki/Drill_bit_sizes

[Bryan B]

Thank you.
As for the narrow end it is 1/2 inch diameter and rounded on the end (rounding helps a lot) but if you try to learn how to make it work with tinder fungus as tinder in one night (many many many strokes one right after another for hours) it will make your hands VERY sore (I still have some small bruised spots after 2 weeks).
With this new optimized piston it is much easier to strike it though.
Also I have polished the cylinder very smooth, I think this will help with a lot of the problems people have with any fire piston and will likely make o-rings last longer.

[jphphotography]

You're probably 100% right about polishing the cylinder, how exactly did you go about doing that? Do you need special tools?

[johnathon007]

A gun cleaning kit and some metal polish come to mind but i haven't started mine to test it yet , going to the store tomorrow to find the stuff to make one.

[C I A H]

a small long drill bit or similar and some super fine sandpaper wrapped around it to run down the shaft would work good too

[monkeyking10]

Do you think it would still have enough compression if the piston were only four inches long, I couldn't find any longer at the store?

[ampstar]

I followed your instructions. My piston is 4.0. Only thing I did that was different is that I didn't file the o-ring slot to an angle. I just cut a deep enough groove around the shaft as I was working with my dremel. Thanks for the instructable man!

[jphphotography]

Right on man, glad to hear it worked out for you. My only concern would be that if the edges of your groove are too sharp they may nick the o-ring when you're installing it and would significantly reduce the lifespan of the o-ring. Just running a file along the edges should be enough. You should post some pictures if you can, I'd like to see the results of what others have made!

[USAFpirate600]

So I am a little confused. The rod goes inside the pipe nipple right? Yet the materials list says1/4 rod and 1/8 pipe nipple? If the rod is bigger than the pipe that makes no sense. Unless you intend for us to turn the rod down until its smaller? Or am I just misunderstanding the directions?

[jphphotography]

That is just what they are called, I have no idea how or where they get the 1/8 part from. I know it sounds wrong but I assure you that wasn't a typo. No need to turn down the rod to fit or anything like that.

[Emiliano Valencia]

ur explanation is completly wrong, it does work like a diesel engine but diesel engines don't work like that. when air is compressed to a point where the partial pressure of oxygen is more than 1.6 it combines with most types of oils and explodes, thats allso why diesel engines make a lot more noise, because they compress the air a lot more than normal gasoline ones.

[madhops0620]

"it does work like a diesel engine but diesel engines don't work like that."

That doesn't even make any sense.  His explanation is correct, and although this is not exactly how diesel engines work, he is giving a comparison to those who do not know very much about this type of combustion.  Also, the compression in a gasoline engine is not what causes the combustion as it does in a diesel engine.  It uses a spark to ignite the fuel, not compression alone.

[chrwei]

a diesel engine doesn't use compression alone either, it requires a certain level of heat to have good combustion, which is why they have glow plugs to preheat the chamber. on a warm day you can start it without glow plugs, but near freezing temps you'll have no luck.

[jongscx]

Well, a Diesel engine doesn't Use the heat, but it just Needs a minimum heat level to function properly... so it kinda does just use compression alone. As opposed to a gas engine which uses both the spark and the compression... In a Diesel engine, the Compression of the fuel-air mixture causes the molecules to heat to the fuel's Flash-point, the point at which it spontaneously ignites. The Fire Piston Works in the same way, where the combustible cotton is placed in the piston with the air and is heated to ignition by the compression of the air.

[JamesRPatrick]

A fire piston works like a diesel engine. A fire piston is not a diesel engine.