Hi, this is Wayne again with a topic “Clickspring: Milling a Fire Piston”.
The ability to make fire without using modern methods is a seriously impressive skill, and even more so, if you can do it using your own custom machine fire piston as a fire starting device. It’S remarkably simple, using adiabatic compression to ignite a piece of tinder that can then be used to start a fire. The one we’re going to make is based around a central cylinder. That’S been drilled out to accept a close, fitting piston. We need a way to clean the inside of the cylinder, so this end cap is removable.
The piston itself has a convenient hollow section that serves as a storage compartment for our tinder, and it’s sealed off with this piston handle and given that we’re likely to be using this while camping i’ve included a small compass inside the end cap, you can download a Set of free plans from makezine.com and to complete this project you’ll need these materials. I purchased the o-rings in a mixed set from my hardware store for a few dollars and the little compass inserts i found online in a pack of 20 for a similar price with free shipping. Now two of them worked perfectly, but the remaining 18 are in a state of navigational confusion. So i guess it’s true.
You do get what you pay for. Okay, let’s start the build by making the cylinder load the stock into the lathe and then take a facing cut to clean off that front. Face extend the stock to mark out the length, make a parting cut and then face the other end spot drill and then drill the central bore to the tap drill size for the end cap thread. We only need a short section of this thread so tap one in to a depth of about a half inch now in this next step, we’re going to drill out the central ball from the other end, but we’d like to leave about a quarter inch of that Thread we just cut at the very end of the ball.
This requires us to drill to a precise depth and ideally we’d use the tailstock graduations to get it exactly correct, but it’s likely that the depth to which we’re drilling exceeds the reach of your lathe tail stock. So here’s a good workaround measure off the correct depth along the length of the drill bit and then simply mark it with a small tape flag now, ideally we’d be using a reamer for this final sizing of the ball. But i want to avoid specifying an expensive cutter like that and for this application i’ve found that a standard twist drill gives a perfectly adequate surface finish and that’s where we’ll leave the cylinder for now.
Next up, let’s turn the end cap from this section of brass rod. Usually i prefer to form an undercut at the base of a thread like this, but in this case we’d like a small filler to help with the o-ring seal. So i’m using a lathe tool with a slight radius on the tip to do the turning a quick tape on the end helps lead. The threading die onto the work and a tail stock die holder, helps keep the die true to the axis of the lathe, while forming that thread aim for the thread to stop just short of the fillet to leave a nice clean curve for the o-ring to seat Into when it’s compressed a quick tidy up of the end of the thread and then it’s over to the mill to put in that cross hole and with that cross hole complete it’s back to the lathe to part off the wood okay before we go any further. Let’S talk a bit about that end: cap seal, it’s based on a design, that’s used widely in hydraulics and pneumatics called an o-ring boss. Seal the threads provide the compression force, but the actual seal is made by the o-ring compressing inside the chamfer. The chamfer can be formed with a common 90-degree countersink, but the fit between the chamfer and seal is critical. I recommend taking gradual cuts and making regular checks at the fit of the seal. As you proceed at this stage, i’m about halfway there and you can see the o-ring is wider than the chamfer.
So when it’s compressed the seal would sit outside and blow out under the pressure to work effectively, the o-ring must sit comfortably inside that chamfer. The best method to determine the depth of cut is to remove the seal altogether and then at the point that the end cap just bottoms on the cylinder. The chamfer is at the perfect depth with the o-ring in place. It compresses to form the seal, leaving a small gap between the cylinder and end cap.
If you should find you’ve gone a little too deep with a countersink just face a little bit off the cylinder and try the fit again with the seal removed. The cylinder can also be used as a convenient way to hold the end cap, whilst the rest of the features are formed. Cut a quick groove pattern on the outside of the cylinder, like the recent metal scriber project bomb. The compass in place with a small spot of epoxy and that’s the cylinder and encap complete next up, is the piston and again we’ve got another trial and fit situation with an o-ring.
I recommend a few test, grooves first to figure out exactly what depth the groove needs to be to accommodate the o-ring that you’ve sourced, if you overshoot just turn off the end and try again until it’s right once you’ve got a tight seal, use, a centre drill To put in a small recess at the end and then insert the piston full depth into the cylinder and mark the end after parting off load, the piston in the lathe and then trim it to just short of that marked length. This will leave a tiny space at the top of the piston when it’s at full compression drill out the center to form the storage compartment and then tap the hole as per the plans. The piston handle is similar to the end cap, although in this case i have undercut that thread to ensure a good seating on the piston and much like the cylinder before we can use the piston as a way to hold the part by the thread face off That parting cut and then form a chamfer. Now i didn’t do it for this project, but there’s a bit of room inside that handle that you could easily bore out and then seal with a basic o-ring cap to make a second storage compartment, insert the paracord to form the lanyard and then turn up a Quick lanyard bead to finish off the project.
Okay, let’s give this thing a test, but before we can do that, we need some tinder and one of the easiest to make is char cloth, find a small tin like this one and then drill an eighth inch hole in the top place. A piece of 100 cotton inside the tin, it’s important that it be cotton, synthetic fabrics, don’t work somewhere, safe outdoors heat up the tin. This little propane torch is perfect for the job, but a camping, stove or a barbecue would work just as well after the paint burns off, you’ll see a little flame coming from the top, and perhaps the sides of the tin. After a few minutes, this flame extinguishes, at which point remove the heat and immediately wrap the tin and some foil to prevent the charcoal from igniting before it cools down when it’s cool, open the tin and if all has gone well, you’ll see a little piece of Char cloth ready for our first test, tear off a small piece and lightly pack, it into the recess at the end of the piston insert the piston, so that the o-ring is just inside the cylinder.
Now the idea is to compress the piston quite forcefully using the full available stroke and it does take quite a few tries to get the hang of it at first, so don’t be discouraged if it doesn’t light off on the first attempt, but after a few shots At it, you’ll see this ignition and a nice glowing ember that you can then use to start a fire drop, the ember into a larger nest of tinder, preferably with some more char cloth inside and before long you’ve got yourself a fire. The spare char cloth can be wrapped in some foil and then packed away into the center of the piston for next time, and a few drops of oil can help that seal work even better as you get more comfortable using it. You’Ll find you can compress the piston just using your hands, getting it to light off. First try most of the time, i’m chris from clickspring, thanks for watching i’ll catch you on the next article.
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