Saw, an instrument usually made of a steel plate with teeth along one edge, used for cutting wood, ivory, stone, and the softer metals. The ancient Egyptians used saws of bronze, and applied them to cutting out planks from logs. The saw was single-handed, and the log was placed on end and secured to posts set in the ground. The inventor of the saw was deified by the Greeks, and called by some Talus and by others Perdix. The saws of the Grecian carpenters were like the straight frame saws of modern times, the blade set across the middle of the frame, with the teeth perpendicular to its plane. The block of wood to be sawn was clamped down upon a bench, and the workmen stood on opposite sides of this, one at each end of the saw. - Saws are of various forms and sizes, according to their intended use. The older forms are straight strips of steel, either set in a frame, or simply provided with handles at each end, so as to be moved forward and back by two persons; or the plate is made stiff enough for a single handle to answer, when it is worked by one person holding it in one hand.

In modern times saw blades are often circular, the teeth cutting as the saw revolves constantly in the same direction. - Steel plates intended for large saws are prepared from ingots carefully made to secure uniform quality, and after being rolled they are slit into the shapes for the different saws. The edge intended for the teeth is then ground true, and the teeth are cut by a punch at a fly press. The rough edges left by the punch are filed down and the teeth are sharpened. The blades are next heated in ovens to a red heat, and then immersed horizontally and edgewise into a trough containing oil with certain portions of melted tallow, beeswax, rosin, pitch, etc. To remove the excess of hardness they thus acquire, after wiping off a portion of the composition that adheres to them, the blades are held over a fire until that which remains ignites; this is called "blazing off." The more that is removed of the composition before this burning, the harder is the blade; and thus its temper is regulated for the kind of saw required.

To give it uniform density throughout, the blade is next hammered over its face upon an anvil or polished steel; this is called "planishing" or "smithing." The next process is grinding the surface, to reduce the thickness of the metal from the teeth toward the back edge. Small blades are held against the stone by means of a board laid upon them, and large saws are suspended at each end. The finishing processes are repetitions of the planishing and grinding, together with polishing by smooth stones and with emery. - The teeth are variously shaped for different saws. The most simple are made by angular notches, the angle at the apex of the notch being of 60°. This is most convenient for sharpening, as the common triangular or "three-square" file is just adapted to its figure. When the teeth are made with equal sides, they are said to have an upright pitch; and when they make a zigzag of alternating long and short lines, they are said to be flat or to have considerable pitch. The former are adapted for cross-cut saws, worked by two men, one at each end. Such teeth lack the chisel-like effect of those of a low pitch, and rather scrape away the wood than tear into it like the latter, which cut only when the saw is moved in the direction toward which the teeth point.

Hand saws in the United States and England have the teeth pointed from the handle; in Asiatic countries and in Greece they have always been made with teeth pointed the other way. A straight cut upon a line can probably be made better by the thrusting cut, and in this the sawdust is thrown out more freely; but the force is certainly applied to better advantage as regards the saw in pulling it in the line of its greatest strength than in pushing; and for very slender saws, in which it is an object to dispense with all unnecessary width and thickness, as in the keyhole and other similar sorts, it would appear decidedly better to adopt the East Indian practice. Some large saws are notched at a sharper angle than 60°, and for these special files made for the angle are used, and are known as mill-saw files. Teeth made at a low pitch in large saws would become clogged with sawdust unless the space between them were enlarged, and the various forms in which this is done give distinctive names to the teeth.

In large mill saws and circular saws the space between the teeth, which may be 2 or 3 in., is hollowed out in a curve, and the outline is much like a fish hook in form, the shank of the hook bending back to make the back of one tooth, and the point curving round to form the under side or face of the next. All saws used for cutting wood require some provision against their liability to become jammed and the teeth clogged in the narrow passage they make for themselves. This is sometimes effected by making the blade thinner toward the back, but the most effectual mode is in the "set" given to the teeth. In finishing the saw the last process is to bend half the teeth a little out on one side, and the other half on the other side. In eastern countries a group of a dozen teeth or thereabout are bent to one side, and the next group to the other. The operation is performed with a small hammer, the saw being held with the teeth resting on the rounded edge of a small anvil. The same may be done with the saw set, which is a bit of steel with slits suited to the different thicknesses of saw blades. The amount of set varies with the sort of service the saw is intended for.

The more likely the material is to clog, the wider must be the spread of the teeth; but if it is an object to avoid the waste of the wood or the greater labor involved in a wide cut, the set should be as little as possible. - Circular saws were in use in 1790, and some forms have been employed for cutting the teeth of clock wheels ever since the time of Dr. Hooke. For cutting wood they were first brought into important service in the machines invented by M. I. Brunei for making ships' blocks, and adopted by the British admiralty board in Portsmouth in 1804. From that time they have continued in constant use and in various forms for different applications. Saws of this kind commonly run in a slit through a table, upon which the board or other material to be sawed is placed and pushed on against the descending teeth. They are made to revolve with great rapidity, and the teeth for those intended to work in soft wood and with the grain are made well apart and inclined and curved even to the fish-hook form. For harder wood the teeth are made smaller and more upright. Insertable teeth, now much used, are placed in notches in the periphery of the saw plate, and when worn down can be replaced.

This contrivance is a great saving, and at the same time allows the dimensions of the saw to be preserved. - The oldest factory for large saws in the United States is probably that founded by William Rowland in Philadelphia in 1802. The largest saws in the world for sawing boards and plank are probably those made expressly for the California market, where they are wanted for the gigantic timber of that region. At the saw factory of Messrs. R. Hoe and co., in New York, circular saws are made of 80 in. diameter and a fourth of an inch thick, and mill and crosscut saws 10 ft. long and upward. At this establishment are produced nearly all the varieties of saws in use, from circular saws of 4 in. diameter up, and from the common wood saw to the largest mill saws. Some of the articles are peculiar to the United States, as also the processes employed. The steel plates are almost entirely imported from England; some are received also from Philadelphia. Chain saws, made of solid links with serrated edges, the links being connected by rivets, are in common use by surgeons for sawing bones when they are so situated that they cannot be operated upon with the common surgeon's saw. They are also sometimes used by mechanics under similar circumstances of position.

Band saws, made by serrating and setting the edge of a flexible steel band, are now largely used in shops for the working and carving of wood, making patterns, etc. They may be of almost any size, from that adapted to the sawing of scrolls in the thinnest boards to the sawing of lumber from logs, and they have the advantage of continuous motion in one direction. The band is moved by means of two rollers covered with leather or vulcanized caoutchouc, one of which is connected with the motor shafting. - The earliest notice of saws being run by power is contained in a manuscript of the 13th century in Paris, in which is a representation of the saw mill with a self action turned by a water wheel. Beck-mann finds evidence of saw mills worked by water power in Augsburg, Germany, as far back as 1322. In the island of Madeira one is said to have been in operation in 1420, and the first one in Norway was built in 1530. In Holland they were in use more than 100 years sooner than in England; and the Dutch furnished the English with lumber.

The operation of one at Lyons in 1555 is described by the bishop of Ely, then British ambassador at Rome. The first recorded attempt to establish a saw mill in Great Britain was made near London in 1663 by a Dutchman; but the enterprise was abandoned on account of the opposition of the hand sawyers. In 1700 the advantages offered by this improvement were set before the public by one Houghton; but no one ventured to introduce it till 1767 or 1768, when by the desire of the society of arts a saw mill was built at Limehouse by James Stansfield. It was soon destroyed by the mob. In the American colonies the importance of this expeditious means of obtaining sawed lumber was generally felt, and efforts were early made to obtain the necessary machinery, such as was used in Holland. In 1634 a saw mill was put in operation at the falls of the Piscataqua, between Berwick and the Cocheco branch of that river, and this is supposed to have been the first mill of the kind in New England. In New York as many as three mills were constructed by the Dutch West India company about 1633, to run by water power or by wind. One of them was on Nut or Governor's island, which was leased in 1639 for 500 merchantable boards yearly, half oak and half pine.

Another was on Saw Mill creek, a small stream which flowed into the East river from the pond known as the Collect. On the Delaware saw mills were erected by the Dutch and Swedes before the arrival of Penn.