Saw


A saw is a tool consisting of a tough blade, wire, or chain with a hard toothed edge. It is used to cut through material, very often wood though sometimes metal or stone. The cut is made by placing the toothed edge against the material and moving it forcefully forth and less forcefully back or continuously forward. This force may be applied by hand, or powered by steam, water, electricity or other power source. An abrasive saw has a powered circular blade designed to cut through metal or ceramic.

Terminology

Saws were at first serrated materials such as flint, obsidian, sea shells and shark teeth.
In ancient Egypt, open saws made of copper are documented as early as the Early Dynastic Period, circa 3,100–2,686 BC. Many copper saws were found in tomb No. 3471 dating to the reign of Djer in the 31st century BC. Saws have been used for cutting a variety of materials, including humans. Models of saws have been found in many contexts throughout Egyptian history. Particularly useful are tomb wall illustrations of carpenters at work that show sizes and the use of different types. Egyptian saws were at first serrated, hardened copper which cut on both pull and push strokes. As the saw developed, teeth were raked to cut only on the pull stroke and set with the teeth projecting only on one side, rather than in the modern fashion with an alternating set. Saws were also made of bronze and later iron. In the Iron Age, frame saws were developed holding the thin blades in tension. The earliest known sawmill is the Roman Hierapolis sawmill from the third century AD and was for sawing stone.
According to Chinese legend, the saw was invented by Lu Ban. In Greek mythology, as recounted by Ovid, Talos, the nephew of Daedalus, invented the saw. In archeological reality, saws date back to prehistory and most probably evolved from Neolithic stone or bone tools. "he identities of the axe, adz, chisel, and saw were clearly established more than 4,000 years ago."

Manufacture of saws by hand

Once mankind had learned how to use iron, it became the preferred material for saw blades of all kinds; some cultures learned how to harden the surface, prolonging the blade's life and sharpness.
Steel, made of iron with moderate carbon content and hardened by quenching hot steel in water, was used as early as 1200 BC. By the end of the 17th century European manufacture centred on Germany, in London, and the Midlands of England. Most blades were made of steel. In the mid 18th century a superior form of completely melted steel began to be made in Sheffield, England, and this rapidly became the preferred material, due to its hardness, ductility, springiness and ability to take a fine polish. A small saw industry survived in London and Birmingham, but by the 1820s the industry was growing rapidly and increasingly concentrated in Sheffield, which remained the largest centre of production, with over 50% of the nation's saw makers. The US industry began to overtake it in the last decades of the century, due to superior mechanisation, better marketing, a large domestic market, and the imposition of high tariffs on imports. Highly productive industries continued in Germany and France.
Early European saws were made from a heated sheet of iron or steel, produced by flattening by several men simultaneously hammering on an anvil After cooling, the teeth were punched out one at a time with a die, the size varying with the size of the saw. The teeth were sharpened with a triangular file of appropriate size, and set with a hammer or a wrest. By the mid 18th century rolling the metal was usual, the power for the rolls being supplied first by water, and increasingly by the early 19th century by steam engines. The industry gradually mechanized all the processes, including the important grinding the saw plate "thin to the back" by a fraction of an inch, which helped the saw to pass through the kerf without binding. The use of steel added the need to harden and temper the saw plate, to grind it flat, to smith it by hand hammering and ensure the springiness and resistance to bending deformity, and finally to polish it. Most hand saws are today entirely made without human intervention, with the steel plate supplied ready rolled to thickness and tensioned before being cut to shape by laser. The teeth are shaped and sharpened by grinding and are flame hardened to obviate sharpening once they have become blunt. A large measure of hand finishing remains to this day for quality saws by the very few specialist makers reproducing the 19th century designs.

Pit saws

A pit saw was a two-man rip saw. In parts of early colonial North America, it was one of the principal tools used in shipyards and other industries where water-powered sawmills were not available. It was so-named because it was typically operated over a saw pit, either at ground level or on trestles across which logs that were to be cut into boards. The pit saw was "a strong steel cutting-plate, of great breadth, with large teeth, highly polished and thoroughly wrought, some eight or ten feet in length" with either a handle on each end or a frame saw. A pit-saw was also sometimes known as a whipsaw. It took 2-4 people to operate. A "pit-man" stood in the pit, a "top-man" stood outside the pit, and they worked together to make cuts, guide the saw, and raise it. Pit-saw workers were among the most highly paid laborers in early colonial North America.

Types of saws

Hand saws

Hand saws typically have a relatively thick blade to make them stiff enough to cut through material. Thin-bladed handsaws are made stiff enough either by holding them in tension in a frame, or by backing them with a folded strip of steel or brass Some examples of hand saws are:
"Back saws," so called because they have a thinner blade backed with steel or brass to maintain rigidity, are a subset of hand saws. Back saws have different names depending on the length of the blade; tenon saw is often used as a generic name for all the sizes of woodworking backsaw. Some examples are:
A class of saws for cutting all types of material; they may be small or large and the frame may be wood or metal.

Circular-blade saws

Most blade teeth are made either of tool steel or carbide. Carbide is harder and holds a sharp edge much longer.
; Band saw blade: A long band welded into a circle, with teeth on one side. Compared to a circular-saw blade, it produces less waste because it is thinner, dissipates heat better because it is longer a right angle to the direction of the wood grain of the workpiece. A crosscut saw is used to make this type of cut.
; Rip cut: In woodworking, a cut made parallel to the direction of the grain of the workpiece. A rip saw is used to make this type of cut.
; Plytooth blade: A circular saw blade with many small teeth, designed for cutting plywood with minimal splintering.
; Dado blade: A special type of circular saw blade used for making wide-grooved cuts in wood so that the edge of another piece of wood will fit into the groove to make a joint. Some dado blades can be adjusted to make different-width grooves. A "stacked" dado blade, consisting of chipper blades between two dado blades, can make different-width grooves by adding or removing chipper blades. An "adjustable" dado blade has a movable locking cam mechanism to adjust the degree to which the blade wobbles sideways, allowing continuously variable groove widths from the lower to upper design limits of the dado.
; Strobe saw blade: A circular saw blade with special rakers/cutters to easily saw through green or uncured wood that tends to jam other kinds of saw blades.

Materials used for saws

There are several materials used in saws, with each of its own specifications.
;Brass: Used only for the reinforcing folded strip along the back of backsaws, and to make the screws that in earlier times held the blade to the handle.
;Iron: Used for blades and for the reinforcing strip on cheaper backsaws until superseded by steel.
;Zinc: Used only for saws made to cut blocks of salt, as formerly used in kitchens
;Copper: Used as an alternative to zinc for salt-cutting saws
;Steel: Used in almost every existing kind of saw. Because steel is cheap, easy to shape, and very strong, it has the right properties for most kind of saws.
;Diamond: Fixed onto the saw blade's base to form diamond saw blades. As diamond is a superhard material, diamond saw blades can be used to cut hard brittle or abrasive materials, for example, stone, concrete, asphalt, bricks, ceramics, glass, semiconductor and gem stone. There are many methods used to fix the diamonds onto the blades' base and there are various kinds of diamond saw blades for different purposes.
;High speed steel : The whole saw blade is made of High Speed Steel. HSS saw blades are mainly used to cut steel, copper, aluminum and other metal materials. If high-strength steels are to be cut, the blades made of cobalt HSS should be used.
;Tungsten carbide: Normally, there are two ways to use tungsten carbide to make saw blades:

Uses

Plainsawing: Lumber that will be used in structures is typically plainsawn, a method of dividing the log that produces the maximum yield of useful pieces and therefore the greatest economy.
Quarter sawing: This sawing method produces edge-grain or vertical grain lumber, in which annual growth rings run more consistently perpendicular to the pieces' wider faces.