A chainsaw (or chain saw) is a portable handheld power saw that cuts with a set of teeth attached to a rotating chain driven along a guide bar. Modern chainsaws are typically gasoline or electric and are used in activities such as tree felling, limbing, bucking, pruning, cutting firebreaks in wildland fire suppression, harvesting of firewood, for use in chainsaw art and chainsaw mills, for cutting concrete, and cutting ice. Precursors to modern chainsaws were first used in surgery, with patents for wood chainsaws beginning in the late 19th century. A chainsaw comprises an engine, a drive mechanism, a guide bar, a cutting chain, a tensioning mechanism, and safety features. Various safety practices and working techniques are used with chainsaws.
History
In surgery
A "flexible saw", consisting of a fine serrated link chain held between two wooden handles, was pioneered in the late 18th century (c. 1783–1785) by two Scottish doctors, John Aitken and James Jeffray, for symphysiotomy and excision of diseased bone, respectively. It was illustrated in the second edition of Aitken's Principles of Midwifery, or Puerperal Medicine (1785) in the context of a pelviotomy. In 1806, Jeffray published Cases of the Excision of Carious Joints, which collected a paper previously published by H. Park in 1782 and a translation of an 1803 paper by French physician P. F. Moreau, with additional observations by Park and Jeffray. In it, Jeffray reported having conceived the idea of a saw "with joints like the chain of a watch" independently very soon after Park's original 1782 publication, but that he was not able to have it produced until 1790, after which it was used in the anatomy lab and occasionally lent out to surgeons. Park and Moreau described successful excision of diseased joints, particularly the knee and elbow, and Jeffray explained that the chainsaw would allow a smaller wound and protect the adjacent muscles, nerves, and veins. While symphysiotomy had too many complications for most obstetricians, Jeffray's ideas about the excision of the ends of bones became more accepted, especially after the widespread adoption of anaesthetics. For much of the 19th century the chainsaw was a useful surgical instrument, but it was superseded in 1894 by the Gigli twisted-wire saw, which was substantially cheaper to manufacture, and gave a quicker, narrower cut, without risk of breaking and being entrapped in the bone. A precursor of the chainsaw familiar today in the timber industry was another medical instrument developed around 1830, by German precision mechanic and orthopaedist Bernhard Heine. This instrument, the osteotome, had links of a chain carrying small cutting teeth with the edges set at an angle; the chain was moved around a guiding blade by turning the handle of a sprocket wheel. As the name implies, this was used to cut bone.
For cutting wood
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