Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 103

The teeth of a hand saw may be hammer-set by securing in a vice a small setting iron, about 6 in. or 7 in. long, shown in end view by Fig. 304. This iron is bevelled at E and F. The saw, of which G is a section, is laid flat on the iron, and tooth H struck with the pene of a small hammer (see Fig. 305), the operator striking every alternate tooth from one side, then every alternate tooth from the other side of the saw plate. Fig. 304 shows bevel E to be somewhat greater than bevel F; the larger teeth are set on bevel E, and the smaller teeth on bevel F. Instead of the block shown by Fig. 304, that illustrated in section by Fig. 306, p. 81, can be employed, but the beginner will prefer the former, as it determines the amount of set. Another device is a steel plate about 6 in. long, with one edge turned over, as at a (Fig. 307); the other edge b is placed in the vice, and the saw c is then laid upon it as shown, being held in position with the left hand. The tooth is then bent over by lightly striking it with the hammer, which bends the tooth to the bevel of plate, as at d (Fig. 308). Another shape of hammer is illustrated by Fig. 309, p. 82, in which pene J is used for setting the coarser teeth and pene K for the finer teeth. Fig. 310 shows a hammer for setting two-handled cross-cut saws, the teeth of which are set in a similar manner to that just described. Fig. 311 shows an end view of the anvil or setting iron, which is larger than that used for a hand saw, and the bevel is longer. L is a section of the saw, and the tooth M comes over the bevel N; every alternate tooth is struck with the poll O of the hammer shown in Fig. 310. Great care is necessary in hammering; never strike the blade of the saw, or it will buckle; this buckling sometimes happens with spring-setting, but in most cases the saw will go back again when setting the opposite side. Saws that are set by the blow of a hammer or punch are apt to be more irregular than spring-set saws; the operation should therefore be very carefully done, and the teeth constantly tried with a gauge or straight-edge, to see that all the teeth are exactly in line. Hammer-set teeth stand well up to their work in cross-grained and knotty wood, whilst spring-set teeth are more inclined to dodge the knots. Some saws have part of the teeth spring-set and part hammer-set, but the difficulty of keeping them exactly uniform neutralises any advantages the plan may possess. Saw teeth are very apt to fracture if given unnecessary set; that is, by trying to get the set from the whole length of the tooth. In connection with this, Disston says that a saw that is easily filed and set is easily made dull, but he dares not make saws as hard as he would like to, until a better method of setting is adopted by the average mechanic, who instead of getting the whole of the set out of the tooth, tries to get part of it from the body of the plate; and, of course, as soon as he gets below the root of the tooth, the saw plate is distorted and strained. This causes a full-tempered saw blade to crack, and ultimately the saw will break at this point.

Fig. 304.—Setting Iron.

Fig. 305.—Hammer-setting Saw Teeth.