Fig. 406.—Anderson’s Expanding Bit.
Fig. 407.—Streers’ Expanding Bit.
Fig. 408.—Clark’s Expanding Bit.
Fig. 409.—Forstner Auger Bit.
AUGERS.
Augers bore well in the direction of the grain of the wood, which centre bits will not do in most woods, unless they have a screw in place of the pin (see Fig. 386, p. 107). Augers are made complete in themselves, and used to bore holes of considerable depth and size in wood. They consist of a steel rod, having a round eye at one end through which a round wooden handle fits at right angles; at the other end is a spiral twist of larger diameter, terminating in a conical screw with a sharp point; the edge of the spiral is a nicker which cuts the grain of the wood around the edge of the hole (see Fig. 410). When using an auger, most power is obtained by standing over the work and boring downwards; a little grease should be used with it. Screw bits replace large augers in cabinet work.
Fig. 410.—Auger.
ABRADING AND SCRAPING TOOLS.
THE USE OF STEEL SCEAPEES.
THE scraper illustrated by Fig. 411, and shown handled by Fig. 412, is an aid in producing surfaces more flat and regular than can be produced with the plane alone. Its use does not dispense with the plane; on the contrary, any surface on which the scraper is to be used must previously be planed as level and smooth as plane can make it. But the plane, in doing its work—no matter how sharp it may be, or how closely the back-iron is set up to the edge of the cutting iron, or how straight across the edge the cutting iron is sharpened—is liable to leave marks and ridges on the face of the work, which, on hard woods, are not effectively removed by the use of glasspaper alone. The scraper is used after the plane has finished its work, and previous to the final operation of glass-papering. In addition to the removal of the ridges left by the plane, the scraper is used for dressing up all kinds of cross-grained surfaces that occur in curly and figured solid and veneer woods; but as far as possible this use of the scraper should be avoided. Excessive dressing up of a cross-grained patch on a panel, a stile, or a tabletop will most certainly show, and spoil the flatness and general appearance of the article when it is polished. As a rule, such excessive scraping is resorted to in consequence of the plane having been sharpened and set badly, or of some other technical oversight or unskilful manipulation.
Fig. 411.—Steel Scrapet.
THE SCRAPER DESCRIBED.
The scraper is a thin and very hard steel plate, about 5 in. by 3 in., or 4 1/2 in. by 2 1/2 in., and slightly less than 1/16 in. in thickness. The long edges are sharpened in a peculiar manner. Both of the long edges may be straight, as in Fig. 411 and at A B, Fig. 413, or one edge may have round corners of differing radii, as at C D. These corners are often useful in working up hollows and mouldings generally. The “straight” edge A B, it will be noticed, is not quite straight throughout its whole length. Near the ends the edge is gradually rounded off, to prevent the corners catching in the surface that is being operated on. In this respect, the commercial scraper (Fig. 411) is incorrectly shaped. The cutting power of a scraper depends upon, first, the quality and temper of the steel of which it is made; and, secondly, upon the proper formation of the burr or feather along its edges. Also, the faces of the steel plate must be perfectly bright and free from rust marks or indentations of any kind. It is by no means an uncommon thing to find any rusty piece of sheet steel—a piece of an old hand-saw or try-square, for example—being used as a scraper. The smallest appreciation of how the scraper cuts would indicate how useless such material is for this particular purpose. On the other hand, scarcely anything better can be found for making a scraper than a piece of broken saw-blade, provided the sides of it are still polished and bright. The fact that the saw was broken may often be taken to indicate a greater hardness than usual in the blade, thus fitting it exactly for the purposes of a scraper. An ordinary saw-blade is not usually hard enough. Provided that there is enough elasticity to “give” in the operator’s hands as it is being pushed along, the scraper should be nearly too hard for an ordinary file to touch. If it can be filed easily, then its edge will soon be gone. At the same time, if the steel is merely hard, without the desired amount of elasticity, the burr edge will strip off as soon as it is applied to the work, leaving a coarse, jagged, and utterly useless edge behind.
Fig. 412.—Handled Steel Scraper.
Fig. 413.—Correctly Shaped Steel Scraper.
Fig. 414.—Diagram showing Action of Scraper.
WHY THE SCRAPER CUTS.
The correctly sharpened scraper is a real cutting tool, and not as its name suggests—and as in practice it often is—a mere abrader of the surface. When in good working trim, the scraper should, if desired, take off shaving after shaving perfectly uniform in thickness, and nearly as wide as the cutting edge is long. But such a performance is rarely required of it, and never when the plane has previously done its work well. Too much emphasis cannot be laid on the fact that the proper duty of the scraper is not to make a surface, but to correct the irregularities on it. In explanation of the cutting action of the scraper, a diagrammatic figure is shown (Fig. 414). This illustration correctly illustrates the cutting principle, though it does not represent a true section of the scraper. In use, the scraper is held firmly in both hands and tilted forwards, away from the operator, until the cutting edge grips the surface of the wood, exactly as shown in Fig. 415. It is then kept steadily at this angle, and made to cut a fine shaving at each stroke as it is being pushed away from the operator in the