To form key-ways by chipping, the object to be chipped is gripped in a vice; and if it is necessary to avoid bruising the surfaces in contact, vice-clamps of lead or copper are employed. If a key-way is to be made in a lever-boss, the two faces are first made tolerably flat and parallel to each other by lathe-turning or other means, and the place and the shape of the key-groove desired is shown by lining the boss with the lines indicated in Fig. 812. The middle line seen is a primary centre line extending along the middle of the lever-arm, from which line, in two directions, the width of the key-groove is scribed. The primary is also used to mark a centre line along the inner surface of the boss or along the hole, to show the centre of the key-way along its entire length, a line at each side of this one also being marked, that the exact width intended along the hole may be seen. By thus lining the faces, and also the hole, both the width of the key-way and its depth into the metal, are indicated. It is necessary for the lines in the hole to be exactly parallel to the axis of the hole, and this result is obtained by means of a square, the blade of which is placed through the hole so that one edge exactly coincides with the primary line on the boss-face, while the pedestal is held in close contact with the face. While thus held, a scriber is moved along the hole and marks the middle line, after which, the square's blade is shifted to an equal distance at either side, in order that the width may be marked.

After the scribing is completed, the mode selected for removing the metal, is that which suits the size of the boss and the quantity to be cut out. If the required key-way is only about two or three inches long, and a quarter or three-eighths wide, the entire chipping may be done with grooving chisels whose cutting edges are about a sixteenth shorter than the finished width of the groove. By chipping with a chisel of such a width, a small quantity of metal will remain at each edge after chiselling, which small portions will be afterwards removed by filing the key-groove to its exact finished width and shape.

Large key-grooves, such as those of one or two inches in width, for bosses of twelve or fourteen inches in diameter, require to be first grooved at each edge of the intended key-ways, which forms two narrow grooves along the entire length of the hole, and leaves a middle superfluous lump still unchipped. This lump is now ready to have other grooves formed therein, the number of which depends on the size of key-way, and, therefore, on the size of the lump.

The chiselling of a key-way which is several inches in length, is performed at opposite ends of the hole, instead of chiselling at only one end, in order that the cutting edge of the chisel may be as near as convenient to the operator. All small key-grooves require occasional bevelling at the ends, during chiselling, as the chisel advances deeper and deeper into the boss, in order to prevent the metal breaking off in an irrregular manner below the place intended.

The amount of filing which is required for any one key-way depends on the amount of care exercised during chipping, to produce smooth surfaces, and to make them uniform; and the larger the groove, the greater is the care requisite. All key-grooves, small and large, should be so finished that their widths are parallel, and their depths or distances into the bosses are slightly taper; for the purpose of causing one entire side of any key-way to bear upon its key, whether the key is partly in or entirely in its place, and to allow a key to be gradually tightened by driving it in, without causing much trouble to get it out, which would be the result if it were parallel. The angle of a key's thickness for securely fixing it permanently, when is required to remain in for many years, should not exceed one degree.