As I said a number of times before, you have to be careful with this blacksmithing stuff.
IT IS ADDICTIVE!!!
But few took heed of the warnings.
Made from old files? There might be a problem there. In recent years, a number of files have been made from soft iron that has had the surface "case hardened" instead of from all good steel. That case hardened layer only adds carbon into the iron a small fraction of an inch of the outside surface area - mostly just the teeth. Inside that is then just junker soft iron with little carbon in it.
Good files are still made from high carbon steel all the way through them. Nicholson is one brand still made that way. But others, especially cheap imports from china tend to be junker iron inside with just that thin outside layer having a high carbon content. It's the internal carbon content in the steel that allows you to heat treat it to use as a flint striker, or to have a good cutting edge on a knife or axe.
So the type of metal inside that old file does have a impact on what you make from it. Really old files tend to be all good high-carbon steel throughout them. But some of the newer ones don't. You can check "spark test" the file with a grinder, but you would have to grind in far enough to get past any possilble surface case-hardening to really tell. And then look for sparks that only fly a short distance, are bright white, and "twinkle" Low carbon soft iron would have long duller red sparks with little "twinkle" in it.
A quick way to check if an old file (that has not been through a fire) to see if it will work to make a flint striker is to carefully grind the teeth off of a section of the thin edge - but cooling it down a lot. If it is getting too hot to hold in your fingers, then cool it right away. You don't want the steel to start turning blue where you are grinding it. Once you have ground down the teeth to full bare metal, then try to strike sparks with your flint. The original heat-treat in the file will still be in the file, and you should be able to get good sparks fairly easily. If not, then the file might not have good high-carbon steel inside it.
When you make your striker, it needs to be heat-treated HARD to then work as a flint striker. What you are doing when you try to strike sparks is to use a sharp edge of your flint to chip/dig out tiny bits of steel from the surface of your striker. The energy you put in to chipping/digging out those tiny bits of steel heats them up enough that the carbon in them burns - those are the sparks you see. The harder you heat-treat your striker, the easier it is to chip/dig out those tiny bits of steel. It needs to be heat-treated just about as hard as you can possibly get it - far harder than a knife blade (those are too soft to spark well). But heat-treating steel that hard also makes it much more brittle and subject to possibly breaking in use. So you can "temper" it back a bit to make it less brittle, but still leave it harder than a knife blade. (And there some other steps you can also take.)
So, was your "old file" good high carbon steel all the way through? And was it heat-treated hard enough? And after you finished making your striker, did you grind down the striking surface of it to clean off any forge scale, and get down to clean bare metal? That "forge scale" gets in the way of striking sparks. Just a couple reasons that it won't spark for you.
I have a description of how I heat-treat my flint strikers on my web site for flint strikers.
http://www.angelfire.com/journal2/firefromsteel
To help "inspire" your next forging session, here's a couple pics of a number of strikers I made up a few weeks ago while ... tinkering ... one Friday. They are all based on original strikers from a number of time periods - from early Roman times through middle ages and Viking era on up into the 1700's and 1800's.
Hope these humble ramblings help. And remember ...
Blacksmithing is ADDICTIVE!
You have been warned!
Mikey - yee ol' grumpy blacksmith out in the Hinterlands