Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 130

Woodworkers use many shapes of boring bits. The pin-bit is like a gouge sharpened both inside and outside. As sold by the tool-dealers, it is sharpened only outside and obliquely, but it will be found that if sharpened inside just a little and both the corners removed (when it becomes a shell-bit, Fig. 375), so that the contact with the wood takes place in the centre of the gouge-like end of the bit, its cutting is improved, while smoothing and polishing all over will allow the chips to escape more freely; this condition is necessary in the working of every cutting tool. The shell bit is only suitable for boring at right angles to the fibre of the wood, the sharp gouge-like edge cutting freely; in a hole of considerable depth the chips have a tendency to remain; it is, however, an excellent bit for boring right through. For boring top and bottom laths for Venetian blinds, etc., and boring pins to hold tenons in their mortises, it is first-rate. When the sharp edge of the shell-bit is ground to a point, it forms what is called a dowel-bit, which is practically the same shape as a spoon-bit (see below), but has a wider stem. The spoon-bit (Fig. 376) resembles the shell-bit, but is pointed to somewhat resemble a tea-spoon, yet is more like the outline of a Gothic arch, the metal being hollowed out to form a cutting edge. This bit bores easily, freely, and well, will enter more exactly where the worker wishes, and is strong and cheap. The nose bit (Fig. 377) is of similar construction. Its cutting edge, from which it derives its name, is a part of the steel bent nearly to a right angle, and sharpened so that it forms a sort of chisel. To avoid catching, the corners are rounded off. For boring across the grain it is not dependable, generally entering half its diameter away from where it was started; but for boring the end-way of the grain the nose bit is efficient and cheap. This bit also must be withdrawn now and then for the removal of chips, or it gets choked. In many ways superior to any of the foregoing is the half-twist or Norwegian bit (Fig. 378), known also as the twist-nose bit. This tool screws itself into the wood, and the chips tend to rise out of the hole. It would not do to bore holes in narrow strips of wood, but for every other purpose it works well in either hard or soft wood any way of the grain. This bit is exactly the same shape as the twist-nose gimlet (Fig. 368). This completes the list of what may be termed shell and twist-type bits. They vary from quite small bits to about 3/4 in. diameter, rarely even being made so large. They can all be obtained in a great variety of sizes, but exact size is not guaranteed, the usual plan being to bore a hole and measure it rather than to measure the bit. A hollow taper bit used for enlarging holes is illustrated by Fig. 379.

Fig. 374.—Thumbscrew Brace.

Fig. 375.—Shell Bit.

Fig. 376.—Spoon Bit.

Fig. 377.—Nose Bit.

Fig. 378.—Twist-nose Bit.

Fig. 379.—Hollow Taper Bit.