The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking. Paul N. Hasluck
and also in Fig. 396. Theoretically, this is quite correct, and under such conditions it would be quite impossible for a bit to overfeed itself. But besides the question of necessary clearance, there is a temptation to make the angle steeper, to help in drawing the bit forward. The length of the nicker and a little experiment will in each case soon determine the most desirable angle. The nicker, too, is occasionally topped off on the outside, as shown in Fig. 394. Faults of boring with a bit so formed are excessive strain on the operator, and a badly finished and more or less oval-shaped hole. The nicker should be, if not quite upright, very nearly so, right down to the point, as shown by the line K L in Fig. 398. This line is not quite parallel to the axis of the bit, being a little nearer to the axis at K than at L. Having sharpened the point of the. nicker from the inside with a file and oilstone slip, take away any feather-edge that may have burred over to the outside by rubbing on the oilstone as shown in Fig. 399, which illustrates the safest way of doing this. To keep the back of the bit to the proper height while it is being rubbed, place on the stone a piece of wood whose thickness will depend upon the size of the bit to be sharpened. The proper shape of the nicker, as seen from the side, is given by Fig. 392. In a new bit there is scarcely any curve, but just a straight slightly sloping edge; if it is correctly made and sharpened there should be a keen edge from S round the curve to about T (Fig. 392). The length of this edge should equal, or slightly exceed, the depth of the thickest shaving the router is capable of removing.
Fig. 399.—Sharpening Centre Bit Nicker.
Fig. 400.—Special Centre Bit.
Fig. 401.—Vertical Boring with Brace.
Fig. 402.—Horizontal Boring with Brace.
HOW TO USE THE CENTRE BIT.
For boring holes across the grain with the centre bit, hold the board firmly on a piece of waste wood, then bore right through into the latter; or bore from the face of the board until just the point of the bit appears at the other side; then reverse the board, place the point in the hole, and finish boring. In boring, see that the chips rise out of the hole; when they do not, remove the bit and shake out the pieces, or the chips may wedge against the tool, and the bit will run to one side or be broken. Boring holes into the end grain of a piece of timber with a centre bit is an operation that sometimes gives trouble. In some woods little pieces of detached material persistently get wedged between the bit and the side of the hole, as at P (Fig. 398). Twist bits are best for this class of work, but when a series of exceptionally clean holes is required in the end grain, and when there is not sufficient room to take the brace and a long twist bit, the specially designed centre bit shown by Fig. 400 will give excellent results. It is made of 1/2-in. steel beaten out, turned up, and filed to the proper shape. The method of holding the brace when boring vertically is shown by Fig. 401, and when boring horizontally by Fig. 402. The use of a hand drill, which for some purposes may be preferred to the ordinary brace, is illustrated clearly by Figs. 403 and 404, the former showing horizontal boring, and the latter vertical boring. A method of getting a true horizontal hole is shown by Fig. 405, a shaped support for the bit being held in the bench vice or in some other manner.
Fig. 403.—Horizontal Boring with Hand Drill.
Fig. 404.—Vertical Boring with Hand Drill.
EXPANDING CENTRE BITS.
The advantages of a bit whose working size can be altered with ease are apparent, and there are a number of such bits on the market. Fig. 406 shows one of the simplest, Anderson’s, this being made in three sizes—5/16 in. to 9/16 in., 9/16 in. to 1 in., and 1 in. to 2 in. Fig. 407 shows Steers’, this being made in three sizes, 5/8 in. to 1 3/4 in., 7/8 in. to 3 in., and 7/8 in. to 4 in., whilst extra cutters for other sizes can be obtained. Clark’s patent bit (Fig. 408) is made in four sizes, 1/2 in. to 1 1/2 in., and 7/8 in. to 3 in., 4 in., and 5 in. respectively. Anderson’s is a cheap bit, the two others being somewhat expensive, though only in first cost, and being thoroughly reliable they obviate the need of a great number of separate bits.
Fig. 405.—Method of Obtaining Accurate Horizontal Boring.
THE FORSTNER AUGER BIT.
The Forstner auger bit (Fig. 409) is a useful tool for smooth, round, oval, or square boring, scroll and twist work. Its speciality is that it is guided by its periphery instead of its centre, and consequently it will bore any arc of a circle, and can be guided in any direction, regardless of grain or knots, leaving a true, polished, cylindrical hollow. It is a great improvement in wood-boring tools. Hitherto, with the exception of the shell bit, which has a gouge-like cutting edge, and is in some respects very defective, the centre bit has been the type of wood-boring tools, for hand use. Some of the twist auger bits are really improved centre bits, and have a screw point in common. All have also a well-polished groove, along which the chips can pass out and relieve the bit, permitting it to cut without the frequent withdrawal that some bits require. With these twist bits and the centre bits as exceptions, all the rest of the wood-worker’s boring tools make a small hole first and gradually enlarge it, especially the spoon bits and the Norwegian twist-nose bits, so that to bore a comparatively large hole in a narrow strip of wood generally implies splitting it. Even the twist auger bits just mentioned are apt to do so by the wedge action of the taper screw. Then some bits bore well in only one way of the grain. Not one of them, however, is capable of boring a part only of a cylindrical hole, that is, they cannot form a semi-cylindrical groove on a piece of wood; every one of them has a tendency to split the wood, and some of them wander from the point at which they are started. The Forstner bit, on the other hand, can be placed close to the edge, or even with part projecting considerably beyond the boundary of the wood, and, with a little care in starting, it will bore its hole or its groove cleanly and well. Then, too, ordinary bits nearly always bore a hole larger than themselves, but the Forstner bit bores truly in the place in which it is set, and truly to the size of itself. It has no