Fig. 2272.
The largest and smallest chisels commonly used in cutting files are represented in two views and half size in [Figs. 2271] and [2272]. The first is a chisel for large rough files; the length is about 3 inches, the width 21⁄2 inches, and the angle of the edge about 50°; the edge is perfectly straight, but the one bevel is a little more inclined than the other; this chisel requires a hammer of about 7 or 8 pounds weight. [Fig. 2272] is the chisel used for small superfine files; its length is 2 inches, the width 1⁄2 inch; it is very thin, and sharpened at about the angle of 35°; it is used with a hammer weighing only 1 or 2 ounces; as it will be seen, the weight of the blow mainly determines the distance between the teeth. Other chisels are made of intermediate proportions, but the width of the edge always exceeds that of the file to be cut. The first cut is made at the point of the file; the chisel is held in the left hand, at a horizontal angle of about 55° with the central line of the file, as at a a, [2273], and with a vertical inclination of about 12° to 4° from the perpendicular, as represented in [Fig. 2274], supposing the tang of the file to be on the left-hand side. The following are nearly the usual angles for the vertical inclination of the chisels, namely: For rough rasps, 15° beyond the perpendicular; rough files, 12°; bastard files, 10°; second-cut files 5°, and dead-smooth-cut files 4°. The blow of the hammer upon the chisel causes the latter to indent and slightly to drive forward the steel, thereby throwing up a trifling ridge or burr; the chisel is immediately replaced on the blank, and slid from the operator until it encounters the ridge previously thrown up, which arrests the chisel or prevents it from slipping farther back, and thereby determines the succeeding position of the chisel. The chisel having been placed in its second position, is again struck with the hammer, which is made to give the blows as nearly as possible of uniform strength, and the process is repeated with considerable rapidity and regularity, 60 to 80 cuts being made in one minute, until the entire length of the file has been cut with inclined parallel and equidistant ridges, which are collectively denominated the “first course.” So far as this one face is concerned, the file, if intended to be single-cut, would be then ready for hardening, and when greatly enlarged its section would be somewhat as in [Fig. 2274].
Fig. 2273.
Fig. 2274.