The chainsaw began as a surgeon's instrument, not a logger's
Before anyone used a toothed chain on trees, two Scottish doctors in the 1780s used a fine serrated chain between wooden handles as a flexible surgical saw. Decades later a German orthopaedist built a hand-cranked chain cutter for bone. Wood-cutting chainsaws only arrived with patents late in the nineteenth century.
The surgeons were John Aitken and James Jeffray, whose flexible saw appeared in the 1785 edition of Aitken's textbook of midwifery. Around 1830 Bernhard Heine, a German precision mechanic and orthopaedist, produced the osteotome: small angled teeth on chain links, driven around a guide blade by turning a sprocket handle. That layout, a chain running around a bar, is exactly what a modern saw uses.
Timber followed. Frederick Magaw of Flatlands, New York, patented a chain sawing machine in 1883 for cutting boards, and Samuel Bens of San Francisco patented a framed version in 1905 hoping to fell giant redwoods. The Canadian millwright James Shand built and patented the first portable chainsaw in 1918, let his rights lapse in 1930, and saw the idea developed by the company that became Festo in Germany. Stihl invented the electric chainsaw in 1926. When World War II cut off German supply, North American makers stepped in, including a firm founded in 1939 that became Pioneer Saws.
Early machines were beasts. McCulloch's first models from 1948 were long-barred two-person tools, some heavy enough to need wheels. A one-person saw arrived in 1950, and by 1959 the average weight was about 12 kilograms; today most weigh 4 to 5. The key breakthrough was the diaphragm carburettor, which uses pressure pulses in the crankcase to draw fuel so the saw runs at any angle, whereas older float-chamber carburettors stalled when tilted.
A centrifugal clutch keeps the chain still at idle, typically 2,500 to 2,700 rpm, and releases instantly when the chain brake fires during kickback. Handles are isolated from the engine on springs or rubber, much like a car's suspension, and some saws have heated grips for cold weather. Battery saws gained ground from the late 2010s, and in the early 2020s Husqvarna and Stihl began offering full-size electric models for cutting logs.
Source: Chainsaw
