saw

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 (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.

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.

The most common measurement of the spacing 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 spacing 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.

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.

Abrasive saws

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

History

Ancient 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 (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."

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 ("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 of 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.

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. (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:

Artillery saw, Chain saw, Portable link saw: a flexible chain saw up to 122 cm (four feet) 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 (7 feet) 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 (6 to 30 inches) 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;

Mechanically powered saws

Circular saw: a saw with a circular blade which spins. Circular saws can be large for use in a mill or hand held up to 24" blades and different designs cut almost any kind of material including wood, stone, brick, plastic, etc.

Table saw: a saw with a circular blade rising through a slot in a table. If it has a direct-drive blade small enough to set on a workbench, it is called a "workbench" or "jobsite" saw. If set on steel legs, it is called a "contractor's saw." A heavier, more precise and powerful version, driven by several belts, with an enclosed base stand, is called a "cabinet saw." A newer version, combining the lighter-weight mechanism of a contractor's saw with the enclosed base stand of a cabinet saw, is called a "hybrid saw."

Radial arm saw: a versatile machine, mainly for cross-cutting. The blade is pulled on a guide arm through a piece of wood that is held stationary on the saw's table.

Rotary saw or "spiral-cut saw" or "RotoZip": for making accurate cuts, without using a pilot hole, in wallboard, plywood, and other thin materials.

Electric miter saw or "chop saw," or "cut-off saw" or "power miter box": for making accurate cross cuts and miter cuts. The basic version has a circular blade fixed at a 90° angle to the vertical. A "compound miter saw" has a blade that can be adjusted to other angles. A "sliding compound miter saw" has a blade that can be pulled through the work, in an action similar to that of a radial-arm saw, which provides more capacity for cutting wider workpieces.

Concrete saw: (usually powered by an internal combustion engine and fitted with a Diamond Blade) for cutting concrete or asphalt pavement.

Pendulum saw or "swing saw": a saw hung on a swinging arm, for the rough cross cutting of wood in a sawmill and for cutting ice out of a frozen river.

Abrasive saw: a circular or reciprocating saw-like tool with an abrasive disc rather than a toothed blade, commonly used for cutting very hard materials. As it does not have regularly shaped edges the abrasive saw is not a saw in technical terms.

Types of blades and blade cuts

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 (so there is more blade to do the cutting, and is usually run at a slower speed.

Crosscut

In woodworking, a cut made at (or close to) 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 ripsaw 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 (HSS)

The whole saw blade is made of High-Speed Steel (HSS). HSS saw blades are mainly used to cut steel, copper, aluminum and other metal materials. If high-strength steels (e.g., stainless steel) are to be cut, the blades made of cobalt HSS (e.g. M35, M42) should be used.

Uses

Saws are commonly used for cutting hard materials. They are used extensively in forestry, construction, demolition, medicine, and hunting.

Musical saws are used as instruments to make music.

Chainsaw carving is a flourishing modern art form. Special saws have been developed for the purpose.

The production of lumber, lengths of squared wood for use in construction, begins with the felling of trees and the transportation of the logs to a sawmill.

Plainsawing: Lumber that will be used in structures is typically plainsawn (also called flatsawn), 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.