I will be cleaning up and fine tuning this tutorial, due to requests I wanted to get something posted quickly. This is a fun and rewarding project and shouldn’t take you longer than one hour to make a fire piston. I will try and obtain the exact dimensions of the brass tube and alluminum shaft (see materials list). If you need tips or additional help please post a comment.
Materials for building a fully functioning fire piston: solid alluminum rod (tried a hollow one on attempt #2 and it didn’t work), brass tube, small ruber o-ring, some fast drying metal filler, drill, vise, drill bits, hack saw, 1 screw, miscellaneous wood for the handle (I used a piece of an oak chair leg), some sand paper, some lubricant (i used petroleum jelly) and some charcloth.
The alluminum rod should fit and slide nicely into the brass tube already, you will just have to find a set that works i dont have the exact dimensions of the tube and rod that i used, but it shouldnt matter. The best test is when your purchasing the alluminum rod and brass tube is to plug the end of the tube with your finger and push and release the rod quickly if you get some resistance and the rod bounces back then your should be fine.
1)cut your peices of tube and rod to the length you want. i put the rod in the tube and cut both peices at the same time.
2)put your rod into your drill to create a make-shift lathe and put your drill into your vice. use your hacksaw as your chisel and try to make a nice groove about 1/2 inch from the bottom of your rod for your o-ring (this is the hardest step to making a fire piston. 
If you make your o-ring grove to deep then your o-ring will not create the seal that is required. its better to make your groove to big and sand down your o-ring for the best fit. A fire piston works by compressing air and without a proper seal it simply won’t work.
3) drill a small hole in the top of your alluminum rod for the screw as well as the material you want to use for the handle.
4) drill a a bigger hole in the bottom of your rod for your fire piston tinder, it doesnt have to be to deep and should be big enough to hold your tinder (charcloth).
5) using a drill bit or a punch slightly widen out the top of your brass tube to better allow your rod to snug its way into the tube.
6) using the metal filler/epoxy (i’ll get the name of it) but its more solid than liquid fill the bottom of your brass tube and leave a bunch of the product on the outside of the tube to form a nice shaped ball and cup it in the palm of your hand for a comfortable fit. 
Also using some of your extra alluminum rod push it down the tube so your filler will be flat inside the tube. your tube is now complete, back to the rod.
7) lighty sand down the rod and put your o-ring on. the o-ring i used had a way smaller diameter than the rod and i had to use a needle to assist on getting the ring on. test for snugness at this time. if your rod goes all the way into the tube with no resistance then try an new o-ring, if its way to hard to push down into the tube, then sand some of the -ring off. 
you will know you have a good seal when you push your rod into the tube and the rod pops back out somewhat (mine popped out about 2 inches, but my tube and rod were long about 8 inches)
attach your handle to your rod, it would be a good idea to drill an indention into your handle, because you dont want your rod to hit the bottom of the tube. their should be a gap between your rod and the bottom of the tube (about 3/16 of an inch).
9) put some lube on your rod and stuff some charcloth into the tinder hole. 
10) give your fire piston the ole college try on my third prototype i got an ember on the 3rd try, but the 4th one i made took on the first go.
[eminimall]
