To illustrate many of the essential operations in making tools, a description of file making is here given. This description applies to a flat tapered file of rectangular cross section. The steel used is a superior grade of high-carbon crucible 26 steel, received from the manufacturers in bars about 12 feet long and of the same cross section as the file. The steps are as follows:

(1) Forging. - A bar is cut into blanks of the length required. Each blank is heated, the tang or handle end is forged by a rapidly working machine hammer, and the taper end is forged by hand.

(2) Annealing. - As the blanks cool, they become somewhat hardened and must be softened by annealing. Several forged blanks are packed in a bulky cast-iron box, and its lid is placed on and luted with clay. Small blanks lose some carbon in heating for forging, and this is restored by packing carbon around the blanks to be annealed. The cast-iron boxes and contents are heated gradually in a furnace to red heat and allowed to cool slowly, occupying two or three days.

(3) Straightening. - When annealed, the blanks are inspected by a man who straightens crooked blanks by tapping with a hammer.

(4) Grinding and Drawfiling. - Straightened blanks are ground on large grind stones to remove scale and expose a clean metal surface. Some blanks are so ground as to remove entirely any de-carburized surface due to heating before forging. The grinding is in some cases supplemented by filing the blanks to make them level across their length, as the stones cannot grind a true flat surface.

(5) Cutting. - The teeth are then cut on the blanks in a machine. A blank lies flat on the lead-covered machine table and is fed in the direction of its length under a wide chisel which is held by the machine and made to oscillate rapidly in a vertical direction or in a direction slightly inclined to the vertical. This chisel strikes the blank and cuts a gash entirely across its width. A double-cut file is run under this chisel twice before the opposite side of the blank is cut. A rasp file is cut by a small chisel resembling a punch which strikes the blank at an angle and raises teeth from its surface. If the blank is bent in cutting the teeth, it is straightened by a lead hammer. This is seldom necessary.

(6) Dipping. - After cutting, the files are usually stamped with the name of the makers, and are then prepared for hardening by dipping into a mixture which forms a film over the surface and prevents oxidation of the tooth points as the file is passed from the heating to the hardening bath. If necessary, this dipping is preceded by a bath of strong alkali to remove grease.

(7) Heating and Hardening. - Each pile is then heated gradually by dipping it into a molten-lead bath kept at a uniform high-temperature by oil burners. It is hardened and tempered in one operation by quenching in salt water.

(8) Cleaning. - After hardening, each file is cleaned by scrubbing, and is further relieved of dirt and clinging particles of metal by subjecting it for a moment to a blast of fine sand and water. This renders the teeth clean and sharp.

(9) Softening Tangs. - The tang ends (handle ends) are then softened by heating in lead and cooling in oil. This keeps the tang from breaking when in use.

(10) Final Inspection - Testing. - Each file is now carefully examined for defects in manufacture, and if perfect, is oiled to prevent rusting. It is then struck on an anvil to detect from the sound any possible flaw, and is tried in filing a piece of metal of standard hardness to discover if it has the right hardness. If these tests are passed, the file is brushed and sent to the packing and shipping department.