Some interesting information presented above. But I would have to disagree with some of it. Just my opinions.
The Fire Piston first showed up in written records in the 14 and 1500's in Europe - as a "scientific curiousity". The archeological evidence down in SE Asia only supports the fire piston in use there for just a couple hundred years - and only after it was known in Europe. Ditto down in South and Central America.
An old file actually will work great as a flint striker. Many modern files will not. So many of them are now made from soft iron (with low carbon content) and then case-hardened on the outside. So only the teeth and a small fraction of an inch of the outside of the file has enough carbon content in it to work as a flint strikers.
The simplest make-it-yourself striker is from an old file. Clamp your file in a vice with around 3 inches sticking up. Drape a shop rag over it, then smack that file on the side with a large hammer - to break/snap off that part sticking above the vice. The rag helps control any "shrapnel", and to help you find that chunk back after it flies across your shop and under a workbench. Now carefully grind off the teeth along the narrow edge - making sure you cool the file often. If it is getting too hot to hold in your fingers, then cool it. Or if you see any blue color developing in the file. Cool it. Also grind the teeth back a bit along the side of that narrow edge a bit, sort of a bevel. And grind off any sharp edges where you snapped it off. Those file teeth get in your way when trying to strike sparks. Plus they chew up the sharp edge on your flint real fast. You will be amazed at how well a file will work as a flint striker. But you will have to use that "pinch" grip to hold it.
What you are doing when you strike sparks is using a SHARP edge on your flint or piece of stone to chip/dig out little bits of steel from the striking surface of your fire steel. The energy you put in to chipping/digging out those little bits of steel (plus the breaking of some molecular bonds and some chemical reactions) heats up those little bits of steel hot enough that the carbon in them burns. Those are the twinkling sparks you see - the carbon burning.
You can use most any stone to strike sparks. The key point is getting a thin SHARP edge on that stone. Chirt, agate, quartz, granit, even slate will work. But the sharp edges you create just wear away lots faster than with flint. With flint you can get better SHARP edges, and they will hold up longer in use.
So you need high carbon steel to begin with. And then it works best when it is heat-treated as hard as you can get it. If your striker is heat-treated too soft, your flint will dig in too much - sort of "grab" the steel. And the bits that it chips out will be too big to get hot enough to burn. The back of a knife blade is generally not hard enough to work well as a flint striker - too soft.
So your striker needs to be heat-treated just about as hard as you can get it to work best as a flint striker. But that does then make it much more brittle and subject to cracking/breaking. So you have to do some other things to cut down on that "brittleness" a bit. Things like that differential quench - where you quench just the striking surface to get it as hard as you can, while leaving the back/handle part softer. Or heat-treating your striker hard, and then "tempering" it a bit - selectively heating it back up to soften it a bit and make it less brittle.
The best tip I ever heard about heat-treating strikers came from a knife maker. He said to ... thermal cycle ... your striker before the final quench. After forging, you heat it up to that point where a magnet will no longer stick to the steel, then pull it out of the heat and let it air cool till you don't see any color. Then do that 2 more times. Then heat back up to critical temp and quench. This releives any internal stress in the steel from forging it, and it shrinks or refines the internal grain structure of the steel. All that will help your striker be less brittle after that last quench.
If you drop any good flint striker on cement or a rock it might crack/break. It is just hardened carbon steel, and will be brittle. And a bad hit on the end or on the handle portion can also crack/break a striker. It is just in its nature - just like the edge on a knife or woodworking chisel. They work best when very hard, but are then more susceptible to cracking/chipping/breaking in use.
I hope these humble thoughts help clear a few things up. And, of course, they are but my humble opinions, and are best used in conjunction with your own research.
Mikey - that grumpy ol' German blacksmith out in the Hinterlands.
Topic: fire pistons (Read 1366 times)