Chainsaw

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.

[4] 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.

[5] 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For much of the 19th century the chainsaw was a useful surgical instrument, but it was superseded in 1894 by the Gigli twisted-wire saw, which was substantially cheaper to manufacture, and gave a quicker, narrower cut, without risk of breaking and being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.

[6] 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.

[8][9] A later patent incorporating a guide frame was granted to Samuel J. Bens of San Francisco on January 17, 1905, his intent being to fell giant redwoods.

[17] Carburetors featuring swivel and floating diaphragms were developed after the war, enabling modern chainsaws to operate in any orientation without the risk of flooding or fuel starvation.

[18] While today's logging operations use a variety of specialized machinery, hand felling with a cable skidder (where tractors and horses may still be utilized) continues to be a viable, cost-effective way to make a living as a logger.

[21] Corded chainsaws became available for sale to the public from the 1960s onwards,[22] but these were never as successful commercially as the older gas-powered type due to limited range, dependency upon the presence of an electrical socket, plus the health and safety risk of the blade's proximity to the cable.

[30] To allow use in any orientation, modern gas chainsaws use a diaphragm carburetor, which draws fuel from the tank using the alternating pressure differential within the crankcase.

The carburetor may need to be adjusted to maintain an appropriate idle speed and air-fuel ratio, such as when moving to a higher/lower altitude or as the air filter clogs.

[citation needed] To prevent vibration induced injury and reduce user fatigue, saws generally have an anti-vibration system to physically decouple the handles from the engine and bar.

[31] This is achieved by constructing the saw in two pieces, connected by springs or rubber in the same way an automobile suspension isolates the chassis from the wheels and road.

Cold temperature can also contribute to vibration-induced injury,[33] and some saws have a small alternator connected to resistive heating elements in the handles and/or carburetor.

[citation needed] Through this hole, grease is pumped, typically each tank filling to keep the nose sprocket well lubricated.

[citation needed] Lateral tensioners have the advantage that the clutch cover is easier to mount, but the disadvantage that it is more difficult to reach nearby the bar.

[citation needed] Consistent improvement to overall chainsaw design, including adding safety features, has taken place over the years.

Since the bar is moving out and inwards depending on the chain length, the oil outlet on the saw side has a banana-style long shape.

Despite safety features and protective clothing, injuries can still arise from chainsaw use, from the large forces involved in the work, from the fast-moving, sharp chain, or the vibration and noise of the machinery.

[37] A common accident arises from "kickback" when a chain tooth at the tip of the guide bar catches on wood without cutting through it.

[citation needed] Another dangerous situation occurs when heavy timber begins to fall or shift before a cut is complete.

[citation needed] Like other hand-held machinery, the operation of chainsaws can cause vibration white finger,[40] tinnitus, or industrial deafness.

Newer, lighter, and easier to wield cordless electric chainsaws use brushless motors, which further decrease noise and vibration compared to traditional petroleum-powered models.

Injury can also result if the chain breaks during operation due to poor maintenance or attempting to cut inappropriate materials.

[citation needed] Gasoline-powered chainsaws expose operators to harmful carbon monoxide gas, especially indoors or in partially enclosed outdoor areas.

[citation needed] Safe and effective chainsaw and crosscut use on federally administered public lands within the United States has been codified since 2016 in the Final Directive for National Saw Program[43] issued by the United States Forest Service, which specifies the training, testing, and certification process for employees and unpaid volunteers who operate chainsaws within public lands.

[citation needed] Chainsaw training is designed to provide working technical knowledge and skills to safely operate the equipment.

[citation needed] When fastened into a special guide frame, a chainsaw can be used as a portable sawmill to cut bulk wood into planks or boards.

The machine is used in construction, for example, in cutting deep, square holes in walls or floors, in stone sculpture for removing large chunks of stone during pre-carving, by fire departments for gaining access to buildings, and in restoration of buildings and monuments for removing parts with minimal damage to the surrounding structure.