Steel Files: Forged, Cut and Hardened

A file is a bar of high-carbon steel, about 1.0–1.25 % carbon, covered in rows of tiny chisel cuts. The blank is forged with a tang, annealed soft, ground flat, and the teeth are raised one by one with a chisel and hammer: each blow cuts a groove and lifts its edge into a tooth. A single-cut file has one row of parallel cuts, at 65–85° to the length; a double-cut file has a second row crossing the first, for general work the first at 40–45° and the second at 70–80°. The file is then hardened as hard as it will go by quenching it in cold brine, and is never tempered; only the tang is softened so it will not snap. Factories do the same steps by machine.