SAW AND SAW-3111.L. The division of wood by riving or splitting was probably the most ancient method of reducing it to pieces of convenient size and shape. If the grain of timber were straight, this plan would have the advantage of economy ; but as it in not so in general, considerable waste is occasioned by riving when the pieces are required to be straight, much wood having to be removed with an adze in order to make it so. Hence the invention of saws.
Saws were used by the ancient Egyptians. The annexed cut repre sents a saw that was discovered, with several other carpenters tools, in a private tomb at Thebes, and which is now preserved in the British Museum. The following cut, from Rosellini's work on Egyptian anti quities, represents a Dian using a similar saw ; the piece of wood which he is cutting being held between two upright posts. In other repre sentations the timber is bound with ropes to a single post; and in one, also copied by Itosellini, the workman is engaged in tightening the rope, having left the saw sticking in the cut. There is a curious picture among tho remains discovered in Herculaneum, representing a carpenter's workshop, with two genii cutting a piece of wood with a frame-saw. On an altar preserved in the Capitoline Museum at ltonre there is a representation of a bow-saw, exactly resembling in the frame and the twisted cord those used by modern carpenters.
Saws are of various forms and sizes. Those used by carpenters and other artificers in wood are the most numerous. Among these arc the following :—The cross-cut saw, for dividing logs transversely, two per sons being employed to pull the saw backwards and forwards, and the teeth being so formed as to cut equally in both directions. The pit-saw, with large teeth, and a transverse handle at each end. It is used for sawing logs into planks, the piece to be eat being laid over a saw-pit six or seven feet deep. One man stands on the log, and the other in the pit, and they pull the saw alternately up and down, the saw cutting in its descent only. The frame-saw is from five to seven feet long, stretched tightly in a frame of timber, the plane of the caw being at right angles with that of the frame. It is used in a similar manner to the pit-saw, but causes less waste, because tho blade, being stretched, may be made much thinner. The ripping-saw, half-ripper, hand-saw, and panel-saw are saws for tho use of one person, the blades tapering in width from the handle. They aro of different lengths, the largest being about twenty-eight inches; and the teeth vary from one-third to one-eighth of an inch. Tenon-saws, sash-saws, dovetail-saws, &c., are very thin, of equal width throughout their whole length, and stiffened with stout pieces of iron or brass fixed on their back edges. These are used for many purposes for which a neat clean cut is required, but where it is not necessary for the whole width of the saw-blade to pass through the wood. and keg-hole saws taper from about an inch to an eighth of, an inch in width, and are used for making curved cuts. Small frame-saws and bow-saws, in which very thin narrow blades arc tightly stretched, arc occasionally used for cutting both wood and metal. Saws are made for cutting bone, iron, brass, and many other hard substances; and there are several varieties used by the carpenter besides what have been enumerated ; but it is unnecessary here to detail them.
The very commonest kind of saws are made of iron-plates, hammer hardened, and planished upon an anvil, to give them some degree of stiffness and elasticity. Tho more useful saws are made either of shear or cast steel. Tho steel is cast in the form of a small slab, about an inch and a half thick. This slab is extended, by rolling, to the re quired degree of tenuity, and then cut, by shears, into pieces of suit able form and size. The edges are next perfected by filing, and bolding the flat side of the plates against large grindstones, which process prepares them for the cutting of the teeth. This operation is usually performed by a die-cutter in a fly-press, the motion of the saw-plate being duly regulated, so that the teeth shall be uniform; the larger teeth being cut one at a time ; and the smaller two, three, or more at a time, according to circumstances. The wire edges left on the teeth by the cutting-out press are removed by filing ; after which the plates undergo the processes of hardening and tempering. They are heated to a cherry-red and clipped into a fatty composition. When sufficiently cooled therein to be handled, they are taken out, and are found to be extremely hard and brittle. They are passed backwards and forwards over a clear charcoal fire, so as to cause the unctuous matter to inflame, or blaze off, as it is termed, which reduces the saws to the required temper ; and, whilst the saw-plates remain hot, any warping they may have acquired in the process is removed by smart blows from a hammer. The next operation is planishing by hammers, to make them more even and equally elastic : after which tho saws are ground on large grindstones. As the grinding impairs the elasticity, they are submitted to a second hammering, and to heating over a coke fire until they attain a faint straw-colour. The marks of the hammer are re moved by again passing the saws lightly over a grindstone ; after which the final polish is given by a fine hard stone, a glazing-wheel covered with buff-leather and emery, or a wooden wheel, called the hard-head. Any defects acquired during these processes are removed by a few blows with a small polished hammer upon a post of hard wood. The saws are " cleaned off" by women, by rubbing fine emery over them lengthwise with a piece of cork-wood. The setter lays each alternate tooth over the edge of a small anvil, and strikes them so as to bend each uniformly into a alight deviation from the plane of the saw ; and then, turning the saw-plate, seta the remaining teeth in like manner, but in the opposite direction. The degree of deviation from the plane of the saw depends upon the kind of wood to be cut; the softest wood requiring the widest or rankest set. Sometimes an instru ment with a notched edge, called a saw- rest, is used for setting the teeth. After being set, the saw is placed, between two plates of lead, in a vice, and the teeth are sharpened with a triangular file. The handles are then fixed on by nuts and screws, and the saws cleaned off, oiled, and packed in brown paper for sale.