FILES AND The file is a steel instrument with sharp ridges or teeth made by the indentations of a chisel, and used in cutting down and shaping metals or other hard substances. It is one of the oldest of hand tools. It is mentioned in the Old Testament scriptures, and probably came into use not very long after man began to work iron. Files were commonly made by hand until about 1850, when machine-made files became general. The first machine proposed for making files was suggested to the French Academy of Sciences in 1702, but it was not until 1812 that the first United States patent on a file-making machine appeared, being taken out by Morris P. Belknap. The files in ordinary uses are made of high grade steel, from 6 to 14 inches in length being the most common sizes. The pointed end that fits into the wooden handle is called a tang, and the corner formed by the junction of the tang to the body of the file is called the heel. Occa sionally they are made with a tang at both ends. The cutting face or faces of a file are formed by the blows of a chisel struck in the file-blank, while the steel is still soft. The closeness and depth of these cuts determines the character of the file, as rough, middle-cut, bastard, second-cut, smooth and dead smooth. When the cuts are crossed so as to form teeth, as in the more common styles, it is a double cut file. When the spacing between the chisel cuts is varied it is "increment Files are also named from their cross-section, as round (usually tapered, for enlarging holes), half round, square or flat. Files for sharpening saws take their names from the kind of saw whose teeth they are shaped to fit, as cross cut file, cant-saw file, pit-saw file, etc. Dentists' files are made with the handle in the centre, and the filing surface on either end. They are styled bicuspid file, plug file, stump file, etc., according to use. A somewhat similar file, only larger, with bent ends, is called a riffier. The files most commonly used by comb-makers are called slitting and topper files.
Double or checkering files, used by cutlers. gunmakers, etc., are practically two files riveted together, with the cutting teeth so placed that one is half way ahead of the other. These are used to produce the checkered effect peculiar to gunstocks. The files used by watchmakers are exceedingly small, fine and delicate, many of them being of less section than a fine sewing needle, and about half the length. These are named according to the part of a watch or clock on which they are used, as clock-pinion file, balance-wheel file, barrel-hole file, etc. The
file proper is not a rubbing or abrading tool, as many n y notechnical persons suppose, but a true cutting tool, whose teeth point in one direction, and which can be used effectively only in that direction, that is when pushed away from the user. The horseshoer's rubber and the ordinary rasp are kindred tools that perform their func tion by being rubbed back and forth, but the file is not intended to be used in that way.
In the case of a rasp, a pointed tool is used to indent the surface of the blank, and this raises prominences on the surface that make it useful as a rubbing or rasping tool. In making files, the blank is first stamped or drop-forged from a high-grade steel, inferior or blistered steel being usable only for rubbers. The' file blank in a soft, unannealed condition, is fixed on the reciprocating carriage of a file-making machine, on a surface of lead designed not to injure the cut side of a file when down. The blank is passed slowly forward under a re ciprocating chisel, whose blows descend on the blank at distances determined by the speed at which the carriage moves. In a common type of machine the chisel is moved upward by a cam and thrown down to deliver Its blow or cut by a powerful spring. The cuts may be deepened by running the blank through the ma chine a second time. Old files may be recut in the same way. After the cutting, the file is hardened by tempering, and is then ready for use. In using a file the filer takes the handle in his right hand, with the back of the hand downward. He takes a firm hold of the point with the left hand, placing the thumb or ball of the thumb on top; or he may reverse the hands to rest his muscles. He advances the file, that is, pushes it away from him, with a parallel motion, bearing down as the file goes forward, and brings it back without pressure. The learner always has a tendency to see-saw or rock the file, which can be overcome only by practice. Unless the file is kept level, the surface cannot be cut down to a level. The use of the file in machine work has been much superseded during recent years by the introduc tion of the emery wheel, operated by 'power, against which the work is held and ground down with much reduced labor. But the emery wheel will not accomplish a great many things that can be done with the hand file, hence its manufacture is not endangered by the increased use of the wheel. See HARDWARE TRADE IN AMERICA.