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.

Description

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.

Terminology

A number of terms are used to describe saws.

Kerf

The narrow channel left behind by the saw and 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 piece of wood into 1 foot sections, with 1/8 inch kerf will produce only seven sections, plus one that is 7/8 inch 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.

Toothed saws

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.

Frequency of teeth

The most common measurement of the frequency of teeth on a saw blade is point per inch. It is taken by setting the tip 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. There is always one more point per inch than there are 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."

Set

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 will be wider than the blade itself. This allows the blade to move through the cut easily without binding. 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.

Other toothed saw terms

  • Back: The edge opposite the toothed edge.
  • Fleam: The angle of the faces of the teeth relative to a line perpendicular to the face of the saw.
  • Gullet: The valley between the points of the teeth.
  • Heel: The end closest to the handle.
  • Rake: The angle of the front face of the tooth relative to a line perpendicular to the length of the saw. Teeth designed to cut with the grain are generally steeper than teeth designed to cut across the grain
  • Teeth: Sharp protrusions along the cutting side of the saw.
  • Toe: The end farthest from the handle.
  • Toothed edge: the edge with the teeth.
  • Web: a narrow saw blade held in a frame, worked either by hand or in a machine, sometimes with teeth on both edges

    Abrasive saws

An abrasive saw has a powered circular blade designed to cut through metal or ceramic.

History

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 cave IV in France. These tools date to 90,000-30,000 years BCE.
In ancient Egypt, open pull saws made of copper are documented as early as the Early Dynastic Period, –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, 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. "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 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.

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:
  • Artillery saw, Chain saw, Portable link saw: a flexible chain saw up to 122 cm long, supplied to the military for clearing tree branches for gun sighting;
  • Butcher's saw: for cutting bone; many different designs were common, including a large one for two men, known in the US as a beef-splitter; most were frame saws, some backsaws;
  • Crosscut saw: for cutting wood perpendicular to the grain;
  • Docking saw: a large, heavy saw with an unbreakable metal handle of unique pattern, used for rough work
  • Farmer's/Miner's saw: a strong saw with coarse teeth;
  • Felloe saw;: the narrowest-bladed variety of pit saw, up to 213 cm long and able to work the sharp curves of cart wheel felloes; a slightly wider blade, equally long, was called a stave saw, for cutting the staves for wooden casks;
  • Floorboard/flooring saw: a small saw, rarely with a back, and usually with the teeth continued onto the back at the toe for a short distance; used by house carpenters for cutting across a floor board without damaging its neighbour;
  • Grafting/grafter/table saw; a hand saw with a tapering narrow blade from 15 to 76 cm long; the origins of the terms are obscure
  • Ice saw: either of pit saw design without a bottom tiller, or a large handsaw, always with very coarse teeth, for harvesting ice to be used away from source, or stored for use in warmer weather;
  • Japanese saw or pull saw: a thin-bladed saw that cuts on the pull stroke, and with teeth of different design to European or American traditional forms;
  • Keyhole saw or compass saw: a narrow-bladed saw, sharply tapered thin to the back to cut round curves, with one end fixed in a handle;
  • Musical saw, a hand saw, possibly with the teeth filed off, used as a musical instrument.
  • Nest of saws: three or four interchangeable blades fitted to a handle with screws or quick-release nuts;
  • One-man cross cut saw: a coarse-toothed saw of 76 to 152 cm length for rough or green timber; a second, turned, handle could be added at the heel or the toe for a second operator;
  • Pad saw: a short narrow blade held in a wooden or metal handle ;
  • Panel saw: a lighter variety of handsaw, usually less than 61 cm long and having finer teeth;
  • Plywood saw: a fine-toothed saw, for cutting plywood
  • Polesaw: a saw blade attached to a long handle
  • Pruning saw: the commonest variety has a 30-71 cm blade, toothed on both edges, one tooth pattern being considerably coarser than the other;
  • Ripsaw: for cutting wood along the grain;
  • Rule saw or combination saw: a handsaw with a measuring scale along the back and a handle making a 90° square with the scaled edge;
  • Salt saw: a short hand saw with a non-corroding zinc or copper blade, used for cutting a block of salt at a time when it was supplied to large kitchens in that form;
  • Turkish saw or monkey saw: a small saw with a parallel-sided blade, designed to cut on the pull stroke;
  • Two-man saw: a general term for a large crosscut saw or ripsaw for cutting large logs or trees;
  • Veneer saw: a two-edged saw with fine teeth for cutting veneer;
  • Wire saw: a toothed or coarse cable or wire wrapped around the material and pulled back and forth.