File

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.