File
Aiton's Encyclopedia (1910)
a steel hand tool having its surface covered with ridges. It is used for shaping metals, wood, and other hard substances. In making, a file is first forged to the required shape and size. While still soft the ridges or serratures are made by blows of a sharp edge like that of a cold chisel. Until the middle of the nineteenth century the cutting of a file was done by hand, but the cutting is now done usually by filemaking machinery. The greatest skill is required in tempering a file. If it be made too hard, the teeth are brittle and break away; if too soft, they are worthless. A file is different from a rasp in that the cutting edges lean slightly toward the point. In use, a file should be pushed from one not rubbed to and fro. Various names are given according to cross section; as the flat, the triangular, the half round, and the round or rat-tail. The end of a file which is fitted into a handle is called by the file maker the tang,--possibly a corruption of tongue. The dentist's file is provided with a roughened surface at each end, the central portion being used for a handle. The smallest files are manufactured for the use of the watchmaker. They are scarcely larger than a cambric sewing needle. When files were made by hand and were necessarily expensive, it was customary to take an old file to the blacksmith to have it softened, resurfaced, and tempered again; but machine-made files are seldom resharpened. According to the latest census report, there are about 3,000 persons in the United States engaged in making files. The annual output is valued at about $3,500,000 reckoned at factory prices.
What Has Changed in the Last Century
The tool Aiton's described in 1910 is still recognisable on any bench: a hardened steel blade cut with teeth that lean toward the point, pushed on the forward stroke, and sold as flat, triangular, half-round and rat-tail, with needle files for watch work. What has gone is the industry behind it — the roughly 3,000 American file cutters and $3,500,000 of annual output have dwindled as production moved abroad, and machine-made files are now treated as consumables rather than sent to a blacksmith to be softened, recut and retempered. Much of the work files once did has also been taken over by angle grinders, rotary tools with tungsten-carbide burrs, coated abrasives and machine tools that leave less metal to remove by hand, while diamond-coated files handle materials too hard for cut steel teeth. The dentist's file has changed most: hand files for shaping cavities gave way to high-speed rotary drills, and the files that remain are chiefly the slender root-canal instruments, many of them made of flexible nickel-titanium rather than carbon steel.
Written for this edition, 2026.