- Saw
Egyptians introduce the metal-toothed saw.
The saw evolved from Neolithic tools. Archeologists have found metal-toothed Egyptian saws dating back to 2000 B.C.E., but China claims that the saw was invented by Lu Ban in the fifth century B.C.E. Early blades were of copper; the Romans then used iron and reinforced the blade at the top, holding it in a wooden frame. In the nineteenth century in Europe a rigid blade of steel with a pistol-grip handle was introduced to produce a more accurate cut.
The cutting edge of a saw blade may be either serrated or abrasive. A handsaw with a stiff serrated blade can cut on both the push and pull strokes, but flexible blades allow cutting on the pull stroke only. Each tooth is bent to a precise angle, called the “set”, which is determined by the saw's intended use. Some teeth are Usually splayed to each side, so that the blade does not stick, or "bind” , in the cut. An abrasive saw uses an abrasive disc or band for cutting.
A number of different categories of hand-powered saws exist, designed either to be pushed forward or pulled backward, or both, and used by one or two people. These were followed by mechanically powered saws, using steam, water, petrol, or electricity, but they all had the same purpose of cutting large pieces of material into smaller ones. Later designs of saw include the circular saw (a rotating metal disc with saw teeth around its edge) and the chain saw (the blade is a chain carrying small cutting teeth).
Samuel Miller's invention of the circular saw in 1777 only came into use when mills became steam- powered. In 1813, Tabitha Babbitt, a Massachusetts Shaker spinner, invented a circular saw as an improvement for lumber production. An early chain saw was developed in 1830 by the German orthopedist Bernard Heine for cutting bone.
SEE ALSO: SHARP STONE BLADE, METALWORKING, AXE, CIRCULAR SAW, BAND SAW, CHAIN SAW
- Scissors
Egyptians create the first fabric cutters.
Spring-type scissors probably date from the Bronze Age. Consisting of blades connected by a C-shaped spring at the handle end, they were used in Egypt from 1500 B.C.E. to Cut silhouettes for artwork.
Pivoted scissors used in ancient Rome and parts of Asia were made of bronze and iron, as were sixteenth- century European ones. Scissors and other implements became more widely used as their quality improved with better methods of metal forging, but cast steel was not used until 1761, when Robert Hinchliffe manufactured scissors in Sheffield. Many were hand- forged with elaborate handles, but the styles were simplified in the nineteenth century to facilitate large- scale mechanical production.
The steel used in scissors contains varying amounts of carbon, depending on the quality of scissors. Drop hammers form the rough shape of the blade from blanks made from red-hot steel bars. The blades are then trimmed and hardened. The steel may contain from 0.55 to 1.03 percent carbon, with the higher carbon percentages providing a harder cutting edge for certain applications.
Surgical and other specialized scissors are made of stainless steel; cheaper scissors are made with softer steel that is cold pressed. Shears used for sheet metal work, called tin snips, have high-leverage handles but are constructed in the same way as scissors.
SEE ALSO: METALWORKING, WELDING, STEEL