Grindstones, Emery Wheels and Oil The sharpening of the cutting-edges of chisels and plane-irons is performed first on a grindstone or on an emery wheel and then finished to a fine edge on an oilstone. Grind stones are natural stones which are turned into circular form and are made of varying diam eters. They are usually arranged to revolve in troughs containing water, but they ought not to run actually in the water as that would tend to soften them and cause them to wear un equally. The water should be fed onto them from a drip-can. They are revolved by a crank handle attached to the axle and malce about 100 revolutions per minute when used for grinding ordinary tools. Various forms of rests or sup ports have been devised for holding the tool during the process of grinding, but in the case of wood-working tools they are seldom used, the workmen usually preferring to hold the tools by hand against the edge of the rotating stone. Grindstones are °trued° or °turned-up) by hand by means of a pointed bar of steel which is constantly rotated during the opera tion so as to always present a new cutting-edge to the stone and they are °trued) mechanically by means of a threaded roller of steel which is clamped in a frame and allowed to rotate against the surface of the stone. Such appli ances are called °grindstone truers.* Emery wheels are similar in appearance to grindstones, but made of powdered emery cemented to gether or of emery cemented to a wooden centrepiece. The cementing material usually em ployed is a silicate insoluble in water and the wheels are usually made in about 10 degrees of coarseness. They are usually of smaller diameter than grindstones and operated at a higher rate of speed. Emery itself is a species of corundum composed of oxide of iron, alumina, silica and a small proportion of lime. The oilstones, sometimes called °hones,* are es sentially fine-grained natural stones which are used for producing the final edge on cutting tools by the process of abrasion, with oil in stead of water to assist the process. They are usually set in wooden stocks and provided with covers to protect them from dust and grit. The principal varieties are the Turkey-, the Charnley Forest, the Arkansas, the Grecian and the Washita stones. As a general rule, oilstones will wear away the most in the mid dle and become hollow both in the direction of their length and breadth. Sometimes, as in the case of the sharpening of jack-plane irons, this hollowing out is somewhat of an advantage as it imparts a desirable curvature to the cutting edge, but when it extends to an inconvenient degree the surface of ,the stone is leveled by being rubbed on a flat sandstone or on an emery slab. Gouges and bead-planes are usually set or sharpened by means of oil-slips or thin slips of oilstone about six inches long and two inches broad and ranging from one-eighth inch to one-half inch in thickness, the edges of which are rounded in a transverse direction to fit the hollow faces of the tools.
Boring tools for wood comprise the various forms of awls, gimlets, augers, bits and braces and the drills.
Awls or bradawls are the simplest forms of boring tools and are used for preparing holes for the adntission of nails and screws. In its ordinary form the awl consists of a small steel rod one end of which is fastened to a wooden handle and the other end double-bevelled to a sharp V-shaped edge by which the fibres of the wood may be compressed and parted so as to form a hole without producing chips and dust The greatest drawback in the ordinary forms is the tendency of the steel rod to pull OUt of the handle when the tool is withdrawn from the hole it has made in the wood. This is especially the case when working in hard woods. In the superior forms this fault is remedied by the use of a hollow handle which contains a number of awls of different sizes, each of which may be fastened to the handle by means of a screw nut.
Gimlets are of awl-form plus a screw. It consists of a small steel rod, one end of which is attached to a wooden handle which forms a T with the rod, and the other end is shaped into the form of a screw. This end consists
of a point in the fOrm of a taper screw and a spiral groove which extends partway of the stem or body as in the case of the "twist-gim lets," or the body may be hollowed out into a nearly semi-cylindrical shell as in the case of the "shell-gimlets." The commonest forms are called "spikes," while other forms are desig nated as "triple-twist" gimlets, "auger" gimlets, "patent-twist" gimlets and "brewers-twist" gim lets, according to the shape of the spiral body. A complete assortment of these tools are usu ally required by a wood-worker.
Augers are merely large gimlets. They are made in both the twisted and the shell forms and are operated by both hands by means of a wooden bar thrust through the eye at the handle end of the stem. Their sizes increase one eighth-inch at a time from three-eighths-inch to two inches in diameter.
Bits and Braces.— The bits comprise the various forms of boring tools such as "centres," "shells," "gouges," "countersinks," etc. They are actuated by the "brace" or "stock." These tools were developed in order to overcome the faults inherent in all forms of awls, gimlets and augers, due to the interruption of the con tinuous rotation of those tools necessitated by the changing of the position of the hands and by the limited amount of pressure applied to the tool. The stock or brace consists of a crank, one end of which is provided with a round head for receiving the pressure of the breast of the operator and the other end re cessed for the reception of the bit. In the earlier forms the bit was secured in the receiv ing end of the brace by means of a thumb screw which engaged a notch near the end of the stem and constituted the weak point of the compound tool. This defect has been remedied in the later forms by the use of various kinds of expanding devices or expand ing-chucks which adapt themselves to all shapes and sizes of stems and hold the bits securely and truly in place. The centre-bit comprises the centre-point, nicker and cutter attached to a shank. The nicker and the cutter are actuated by the brace and rotate about the centre-point. It is used for boring large and deep holes. The countersinks are made in a great variety of forms and are designated as "snail-horn," "rose-head" and "flat-head" according to the shape of the cutting point. In wood work they are employed for enlarging the entrances of holes when it is desired to let the heads of screws or bolts lie completely below the sur face of the wood. Some of the other useful forms of bits actuated by the brace are the "screw-driver" bit, the shank end of which is square-tapered to fit the socket of the brace and which being turned with the brace is quicker in its action than that of a hand-worked screw-driver; the "taper" bit for boring fun nel-shaped holes; the "shell" bit, the cross section of which is composed of a convex and concave curve roughly semi-circular in form; the "nose" bit, a shell bit provided with a nose or lip at the cutting-point for the withdrawal of the core from the wood; the "spoon" bit, the cutting-edge of which is formed in the shape of a parabola and, therefore, does not draw out the core as effectually as the nose bit; and the "gouge" bit, the cross-section of which is similar to that of the gouge and is simply rounded at the cutting-point without the provision of a nose or lip. In the ordinary forms of the compound tool the brace is ro tated through complete revolutions, thus pre venting the boring of holes or the driving of screws in one side of a corner at a distance any closer to the adjacent side than that which is equal to the radius of revolution, but this shortcoming of the tool is remedied in the hatchet brace in which the brace acts as a lever which moves the bit around and at the same time feeds it forward by means of a ratchet and click actuating a square-threaded feed-screw, as the brace is moved back and forth through partial revolutions.