Legend has it that Jim Bowie's original Bowie Knife was made by for him by his brother (apparently a blacksmith) from an old file.
The high-carbon steel in a file and the hard tempering give it a superior edge, but file blades can also be brittle. I have a worn-out foot long file I plan on turning into a dagger. To avoid it breaking, I annealed it by heating it red-hot in my forge, then allowing it to cool slowly. When I have it shaped the way I want, I plan on covering the spine of the blade with clay, then tempering it. Theoretically, it should keep the spine flexible and harden up the edge. From what I've read, this is how Japanese swords were done.
Will it work? I have no idea. If it doesn't, I'm out three bucks (all hail Harbor Freight
www.harborfreight.com/)
K'Jev