SAW MANUFACTURE. Saws were used the ancient Egyptians ; a specimen, found among the tombs of Thebes, is deposited in the British Museum. There is a picture among the remains discovered in the ruins of Herculaneum, representing the interior of a carpenter's workshop, with two genii cutting a piece of wood with a frame-saw; and on an altar preserved in the Capitoline Museum at Rome there is a perfect representation of a bow-saw, exactly resembling, in the form of the frame, and the twisted cord for tightening it, those used by modern carpenters.
Saws are of various forms and sizes, accord ing to the purposes to which they are to be applied. The Cross Cut Saw is used for dividing logs transversely. The Pit Saw, a long blade of steel with large teeth, and a ,transverse handle at each end, is used for sawing logs into planks or scantlings. The Frame Saw is a blade from five to seven feet long, used in a similar manner to the pit saw, but it causes less waste, because the blade; being stretched in a frame, may be made much thinner. The Ripping Saw, Half Ripper, Hand Saw, and Pannel Saw, are saws for the use of one person, the blades tapering in width from the handle. Tenon Saws, Sash Saws, Dovetail Saws, &c., are made of very thin blades of steel, of equal width throughout their whole length, and stiffened with stout pieces of iron or brass fixed on their back edges. Compass Saws and Key Hole Saws are long narrow saws, tapering from about an inch to an eighth of an inch in width, used for making curved cuts. Small Frame Saws and Bow Saws, in which very thin narrow blades are tightly stretched, are occasionally used for cutting both wood and metal. Saws are made for cutting bone, iron, brass, and many other hard substances.
The very commonest kind of saws are made of iron-plates, hammer-hardened, and planish ed upon an anvil, to give them some degree of stiffness and elasticity. The more useful saws are made either of shear or east steel. The steel, reduced to thin sheets, is cut into pieces of suitable size and shape. The edges are perfected by filing, and holding the fiat sides of the plates against large grindstones, which process prepares them for the cutting of the teeth. This operation is usually per by a die-cutter in a fiy-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 pro , cesses of hardening and tempering. The next
operation is planishing by hammers, to make them more even and equally elastic; after which the saws are ground on large grind stones. The plate is held against the circular face of the stone by an interposing board, against which the grinder presses with all his force, in order to grind it as evenly as possible. He stands on tip-toes, stretching over the stone, which revolves with great rapidity; his hands, arms, breast, and knees being all brought into action to produce the desired effect. As this grinding impairs the flatness and elasticity of the saw-plates, they are sub mitted to a second hammering by the pla nishers, and their elasticity is restored by heating them over a coke fire until they attain a faint straw colour. The marks of the ham mer are removed 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. After being cleaned by women, the saws are handed to the Seller, who lays each alternate tooth over the edge of a small anvil, and strikes them so as to bend each uniformly into a slight deviation from the plane of the saw, and then, turning the saw-plate, he sets the re maining teeth in like manner, but in the oppo site direction : sometimes peculiar tools are used for this setting. After being set, the saw is placed between two plates of lead, in a vice, and the teeth are sharpened with a tri angular file. The size, form, and sharpness of the teeth, vary according to the purpose to which the saw is to be. applied. The handles are then fixed on by nuts and screws, and the saws cleaned off, oiled, and packed in brown' paper for sale.
Saws for cutting stone are without teeth, although they are sometimes slightly notched upon the cutting edge, that they may collect and retain the particles of sand that are con ducted into the cut by a small current of water, and by the attrition of which the effect is mainly produced. The saw plate is tightly stretched in a kind of rectangular frame, of which it forms the lower side ; and the frame, being suspended by ropes, is moved backwards and forwards by one or two men.
The saw manufacture is one of the most in teresting departments of the industry at Shef. field. Saws are made in that town to an im mense extent.