Saw

A saw is a tool consisting of a tough blade, wire, or chain with a hard toothed edge used to cut through material. Various terms are used to describe toothed and abrasive saws.
Saws began as serrated materials, and when mankind learned how to use iron, it became the preferred material for saw blades of all kinds. There are numerous types of hand saws and mechanical saws, and different types of blades and cuts.
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.
A number of terms are used to describe saws.
The narrow channel left behind by the saw and (relatedly) the measure of its width is known as the kerf. As such, it also refers to the wasted material that is turned into sawdust, and becomes a factor in measurements when making cuts. For example, cutting an 8-foot (2.4 meter) piece of wood into 1 foot (30 cm) sections, with 1/8 inch (3 mm) kerf will produce only seven sections, plus one that is 7/8 inch (21 mm) too short when factoring in the kerf from all the cuts. The kerf depends on several factors: the width of the saw blade; the set of the blade's teeth; the amount of wobble created during cutting; and the amount of material pulled out of the sides of the cut. Although the term "kerf" is often used informally, to refer simply to the thickness of the saw blade, or to the width of the set, this can be misleading, because blades with the same thickness and set may create different kerfs. For example, a too-thin blade can cause excessive wobble, creating a wider-than-expected kerf. The kerf created by a given blade can be changed by adjusting the set of its teeth with a tool called a saw tooth setter. The kerf left behind by a laser beam can be changed based on the laser's power and type of material being cut.
A toothed saw or tooth saw has a hard toothed edge. The cut is made by placing the toothed edge against the material and moving it back and forth, or continuously forward. This force may be applied by hand, or powered by steam, water, electricity or other power source.
The most common measurement of the frequency of teeth on a saw blade is point per inch (25 mm). It is taken by setting the tip (or point) of one tooth at the zero point on a ruler, and then counting the number of points between the zero mark and the one-inch mark, inclusive (that is, including both the point at the zero mark and any point that lines up precisely with the one-inch mark). There is always one more point per inch than there are teeth per inch (e.g., a saw with 14 points per inch will have 13 teeth per inch, and a saw with 10 points per inch will have 9 teeth per inch). Some saws do not have the same number of teeth per inch throughout their entire length, but the vast majority do. Those with more teeth per inch at the toe are described as having incremental teeth, in order to make starting the saw cut easier.
An alternative measurement of the frequency of teeth on a saw blade is teeth per inch. Usually abbreviated TPI, as in, "a blade consisting of 18TPI." (cf. points per inch.)
Set is the degree to which the teeth are bent out sideways away from the blade, usually in both directions. In most modern serrated saws, the teeth are set, so that the kerf (the width of the cut) will be wider than the blade itself. This allows the blade to move through the cut easily without binding (getting stuck). The set may be different depending on the kind of cut the saw is intended to make. For example, a ripsaw has a tooth set that is similar to the angle used on a chisel, so that it rips or tears the material apart. A "flush-cutting saw" has no set on one side, so that the saw can be laid flat on a surface and cut along that surface without scratching it. The set of the blade's teeth can be adjusted with a tool called a saw set.
An abrasive saw has a powered circular blade designed to cut through metal or ceramic.
Saws were at first serrated materials such as flint, obsidian, sea shells and shark teeth.
Serrated tools with indications that they were used to cut wood were found at Pech-de-l'Azé caveIV in France. These tools date to 90,000-30,000 years BCE.
In ancient Egypt, open (unframed) pull saws made of copper are documented as early as the Early Dynastic Period, c. 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 were used for cutting a variety of materials, including humans (death by sawing), and models of saws were used in many contexts throughout Egyptian history. Particularly useful are tomb wall illustrations of carpenters at work that show the sizes and use of different types of saws. Egyptian saws were at first serrated, hardened copper which may have 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. "[T]he identities of the axe, adz, chisel, and saw were clearly established more than 4,000 years ago."
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 ("case hardening" or "steeling"), 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, (the Bergisches Land) in London, and the Midlands of England. Most blades were made of steel (iron carbonised and re-forged by different methods). In the mid 18th century a superior form of completely melted steel ("crucible cast") 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 (and actually prevent) 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.
A pit saw was a two-man ripsaw. 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.
Hand saws typically have a relatively thick blade to make them stiff enough to cut through material. (The pull stroke also reduces the amount of stiffness required.) 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 (formerly iron) or brass (on account of which the latter are called "back saws.") Some examples of hand saws are:
"Back saws" which have a thin 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" (from use in making mortise and tenon joints) 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.
Most blade teeth are made either of tool steel or carbide. Carbide is harder and holds a sharp edge much longer.
There are several materials used in saws, with each of its own specifications.
Salaman, R A, Dictionary of Woodworking Tools, revised edition 1989