How does a chainsaw work? Private1 month ago - Automobiles - Ban Lŭng - 19 views
What is a chainsaw?
The clue is in the name! A chainsaw has two main parts: a saw blade built into a chain, wrapped around a long metal guide bar, and a small, one-cylinder gasoline (petrol) engine (sometimes an electric motor powered by a cord or battery pack). The chain is a bit like a bicycle chain, running around sprockets (gear wheels designed to turn a chain) only with about 30 or so sharp teeth (made from a hardened steel alloy) mounted around it at intervals. Inside the engine, as the piston moves in and out of the cylinder, it pushes a connecting rod that turns a crankshaft. The crankshaft turns gears that are connected (through a centrifugal clutch, explained below) to one of the sprockets on which the chain is mounted—and the chain spins around.
The fuel you put in a chainsaw's gas tank contains, in chemical form, all the energy you'll consume cutting down and chopping up logs. To keep it nice and light, a typical chainsaw tank holds just 0.5 liters (1.1 US liquid pints) of gas (a car's gas tank holds maybe 45–55 liters or 12–15 US liquid gallons, which is roughly 100 times more).
The fuel feeds through a carburetor to mix it with air.
A chainsaw engine runs all the time, but you don't want the chain spinning unless you're actually cutting wood, like using it as a brush cutter machine: that's dangerous and it wastes energy. The clutch solves this problem. As explained in more detail below, the centrifugal clutch connects the engine and the chain when the engine speed is fast (when the operator pulls on the throttle) and stops the chain from spinning when the engine speed is low (when the chainsaw is just idling).
Gears carry power from the clutch to the sprocket that holds the chain.
The chain spins around the edge of a long-steel plate called the guide bar, spitting out wood dust as it goes!
Advantages and disadvantages of chainsaws
The main advantage of using a chainsaw(like when used as a hedge trimmer)—speed—is fairly obvious. It would be hard to spend an entire day chopping your way through a forest with a handsaw, but you could certainly do that with a chainsaw.
The two biggest drawbacks of chainsaws are safety and maintenance. Although chainsaws can be used by any fairly strong adult (after suitable training) and many practical uses like earth auger, they are nevertheless inherently dangerous. (I have the manual for a Stihl MS270 chainsaw open beside me as I write this and it's interesting to note that about 16 of the 64 pages—fully a quarter of the text—is devoted to warnings and safety precautions.) The biggest risk comes from a problem called kickback, where the chain catches on something but the engine keeps turning, so the whole saw flies up and backward toward your head (think action and reaction—Newton's third law of motion), potentially causing fatal injuries. Chainsaw helmets with visors offer some protection; so too do chainsaw uniforms (made from synthetic fibers such as nylon, which snag up the chainsaw teeth and bring the machine quickly to a halt).