FILE, a well-known steel instrument, having teeth on the surface for cutting metal, ivory, wood, Sic.
When the teeth of these instruments are formed by a flat sharp-edged chissel, extending across the surface, they are properly called files ; but when the tooth is formed by a sharp-pointed tool, in the form of a triangular pyramid, they are termed rasps. The former are used for all the metals harder than lead or tin ; and the latter for the softer metals, ivory, bone, horn, and wood.
Files are dhided into two varieties, from the form of their teeth. When the teeth are a series of sharp edges, raised by the flat chissel, appearing like parallel furrows, either at right angles to the length of the file, or in an oh ' lique direction, the files are termed single cut. But when these teeth are crossed by a second series of similar teeth, they are said to be double cut. The first are fitted for bras and copper, and are found to answer better when the teeth run in an oblique direction. The latter are suited for the harder metals, such as cast and wrought iron and steel. Each tooth presents a sharp angle to the substance, which penetrate the substance, while the single cut file would slip over the surface of these metals. The double cut file is less fit for filing brass and copper, since the teeth would be very liable to be clogged with the filings.
Files arc called by different names, according to their various degrees of fineness. Those of extreme roughness are called rough ; the next to this is the bastard cut ; the third is the second cut ; the fourth the smooth ; and the finest of all the dead smooth. The very heavy square files used for heavy smith-work, are sometimes a little coarser than the rough ; they are distinguished by the name of rub bers.
Files are also distinguished for their shape, as fiat, half round, threc•square, four-square, and round. The first are sometimes of uniform breadth and thickness throughout, and sometimes tapering. The cross section is a parallelo gram. The half-round is generally tapering, one side be ing flat, and the other rounded ; the cross section is a seg ment of a circle, varying a little for different purposes, but seldom equal to a semicircle. The three-square generally
consists of three equal sides, mostly tapering ; those which are not tapering are used for sharpening the teeth of saws. The four-square has four equal sides, the section being a square. These files are generally thickest in the middle, as is the case with the smith's rubber. In the round file, the section is a circle, and the file generally conical.
The heavy and coarser kind of files are made from the inferior marks of blistered steel. That made from the Russian iron, known by the name of old sable, and also called from its mark CCND, is an excellent steel for files. Some of the Swedish irons would doubtless make the best file steel, but their high price would be objectionable for heavy articles.
The steel intended for files is more highly converted than for other purposes, to give the files proper hardness. It should, however, be recollected, that if the hardness is not accompanied with a certain degree of tenacity, the teeth of the file break, and do but little service.
Small files are mostly made of cast steel, which would be the best for all others, if it were not for its higher price. It is much harder than the blistered steel, and from having been in the fluid state, is entirely free from those seams and loose parts so common to blistered steel, which is not sounder than as it came from the iron forge before conver sion.
The smith's rubbers are generally forged in the common smith's forge, from the converted bars, which are, for con venience, made square in the iron before they come into this country. The files of lesser size are made from bars or rods, drawn down from the blistered bars and the cast ingots, and known by the name of tilted steel.
The file maker's forge consists of large bellows, with coak as fuel. The anvil block, particularly at Sheffield, is one large stone of millstone girt. This anvil is of consi derable size, set into and wedged fast in the stone. The anvil has a projection at one end, with a hole to contain a sharp-edged tool for cutting the files from the rods. It also contains a deep groove for containing dies or bosses for giving particular forms to the files.