Saw

Saw

A crosscut hand saw about 620 mm (24 inches) long
Classification Cutting
Types Hand saw
Back saw
Bow saw
Circular saw
Reciprocating saw
Bandsaw
Tenon Saw
Related Milling cutter

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. 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.

Terminology

Diagram showing the teeth of a saw blade when looking front-on. The teeth protrude to the left and right, so that the saw cut (kerf) is wider than the blade width. The term set describes how much the teeth protrude. The kerf may be sometimes be wider than the set, depending on wobble and other factors.

History

Roman sawblades from Vindonissa approx. 3rd to 5th century AD

Saws were at first serrated materials such as flint, obsidian, sea shells and shark teeth.[2]

In ancient Egypt, open (unframed) saws made of copper are documented as early as the Early Dynastic Period, circa 3,100–2,686 BC.[3] Many copper saws were found in tomb No. 3471 dating to the reign of Djer in the 31st century BC.[4] Saws have been used for cutting a variety of materials, including people (see Death by sawing). 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.[2] The earliest known sawmill is the Roman Hierapolis sawmill from the third century AD and was for sawing stone.

Bronze-age saw blade from Akrotiri, late Cycladic period c. 17th century BC

According to Chinese legend, the saw was invented by Lu Ban.[5] In Greek mythology, as recounted by Ovid,[6] 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."[7]

Manufacture of saws by hand

Once mankind had learned how to use iron, this 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 by quenching hot iron in water, was used as early as 1200 BC.[8] By the end of the 17th century European manufacture centred on Germany (the Bergisches Land) and in London and the Midlands of England. Most blades were made of steel (iron carbonised and re-forged by different methods).[9] 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.[10] 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.[11] 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.[12] 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 <Barley ibid p11> 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 <Moxon, ibid>. 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 <Moxon, ibid, p95>. 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 <Barley ibid pp5–22>. 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 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"[13] with either a handle on each end or a frame saw. A pit-saw was also sometimes known as a whipsaw.[14] 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.[15] Pit-saw workers were among the most highly paid laborers in early colonial North America.

Types of saws

Hand saws

Rip sawing circa 1425 with a frame or sash saw on trestles rather than over a saw pit

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

"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:

Frame saws

A class of saws for cutting all types of material; they may be small or large and the frame may be wood or metal.

Mechanically powered saws

Circular-blade saws

Circular wood-cutting saw at Maine State Museum in the capital city of Augusta, Maine
This particular circular saw, which cut wood into segments to fit a wood-burning kitchen stove, is displayed at the Cole Land Transportation Museum in Bangor, Maine.
Reconstruction of the hydraulic saw by Leonardo da Vinci (Codice Atlantico foglio 1078) exposed at the Museo nazionale della scienza e della tecnologia Leonardo da Vinci, Milan.

Reciprocating blade saws

Continuous band

Chainsaws

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 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 (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.
Tungsten carbide
Normally, there are two ways to use tungsten carbide to make saw blades:
  1. Carbide-tipped saw blades: The saw blade's teeth are tipped (via welding) with small pieces of sharp tungsten carbide block. This type of blade is also called TCT (Tungsten Carbide-Tipped) saw blade. Carbide-tipped saw blades are widely used to cut wood, plywood, laminated board, plastic, grass, aluminum and some other metals.
  2. Solid-carbide saw blades: The whole saw blade is made of tungsten carbide. Comparing with HSS saw blades, solid-carbide saw blades have higher hardness under high temperatures, and are more durable, but they also have a lower toughness.

Uses

A man recording the sound of a saw for sound effect purposes in the 1930s

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.

See also

References

  1. ↑ Barley, Simon "British Saws and Saw Makers from c1660, 2014
  2. 1 2 P. d'A. Jones and E. N. Simons, "Story of the Saw" Spear and Jackson Limited 1760-1960
  3. ↑ Walter B. Emery Excavations at Saqqara, The Tomb of Hemaka and Hor-Aha, Cairo, Government Press, Bulâq, 1938 (2 vols)
  4. ↑ http://www.touregypt.net/featurestories/firstdynastysaqqara.htm The 1st Dynasty Tombs of Saqqara in Egypt by John Watson
  5. ↑ Lu Ban and The Invention of the Saw History Anecdote at Cultural China website
  6. ↑ Ovid Metamorphoses Bk VIII:236-259: The death of Talos A. S. Kline translation, Electronic Text Center at University of Virginia Library
  7. ↑ Richard S. Hartenberg, Joseph A. McGeough Neolithic Hand Tools at Encyclopædia Britannica Online
  8. ↑ Jones & Simons, Story of the Saw, p15
  9. ↑ Moxon, J: Mechanick Exercises, p95-99
  10. ↑ Barley, Simon, British Saws and Saw Makers from c1660, p7
  11. ↑ Barley, ibid p42
  12. ↑ Tweedale, G., Sheffield Steel and America, ch 11
  13. ↑ Charles W. Upham Salem Witchcraft with an account of Salem Village and a History of Opinions on Witchcraft and Kindred Subjects. Frederick Unger, New York, 1978 (Reprint), 2 vols., vol. 1, p 191
  14. ↑ Glossary of Tools at (American) Pilgrim Hall Museum website
  15. ↑ Massingham, H. J., and Thomas Hennell. Country relics; an account of some old tools and properties once belonging to English craftsmen and husbandmen saved from destruction and now described with their users and their stories. Cambridge, Eng.: University Press, 1939.reprint 2011 ISBN 9781107600706 books.google.com/books?id=6_auYCccqoQC&pg

Salaman, R A, Dictionary of Woodworking Tools, revised edition 1989

Further reading

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