Saw chain
The chainsaw's namesake component, the saw chain, is the part of the machine that actually cuts into wood. When the chainsaw is in operation, the motor propels the saw chain around a guide bar at high speeds, allowing the teeth to cut chips from the side and bottom. Somewhat counter-intuitively, modern saw chains feature depth gauges that limit the depth of cut on each individual tooth. Making sure that individual teeth do not bite too deeply into the wood stops the chain from binding in the wood and allows efficient, safe operation of the tool.
Guide bar
A chainsaw's guide bar is a long, rounded piece of metal, usually made from a wear-resistant steel alloy. Guide bars typically range from 16 to 36 inches long. An edge slot around the outside of the bar guides the cutting chain and holds it in position. The operator controls the machine by positioning the guide bar against the object he wishes to cut. Previously, loop-style guide bars known as bow bars were used to buck logs and clear brush, but they are now almost never used due to their increased risk of injury.
Throttle
The chainsaw's throttle controls the supply of fuel to the engine and thus controls the saw's revolutions per minute. Thus, the throttle allows the chainsaw's operator to increase or decrease the saw's speed as necessary to adapt to different jobs. As a safety mechanism, modern chainsaws automatically stop the chain as soon as the operator releases pressure on the throttle.
Engine control
The engine connects to the cutting chain itself by means of a clutch and a sprocket. Among the clutch's functions is to keep the engine from stalling if the chain abruptly slows or stops, a fairly common occurrence when cutting through hard or frozen wood. Another is to prevent the chain from rotating while the engine is idling, preventing accidental damage to the saw or injury to the operator. A well-tuned clutch keeps the machine running efficiently and consistently, improving safety and performance.
Decompression valve
The decompression valve releases air compression produced by operating the saw. Eliminating this compression makes starting the chainsaw much easier. It reduces the energy required to pull the starter cord, makes a strong ignition spark, and produces an ideal air-fuel mixture in the engine.
Noise control
Because they operate at very high speeds, chainsaws tend to produce a lot of noise. In particular, larger chainsaws with gasoline-powered engines tend to be extremely noisy devices. Mufflers work to at least somewhat reduce the noise output; they not only keep the operator's neighbors happy but also help the operator himself stay aware of his surroundings, thereby improving safety. Note that smaller electric chainsaws naturally make less noise and thus require less noise control.
Chain stoppers
Given their impressive cutting power, chainsaws are potentially very dangerous devices. One of these devices is the chain catcher, a metal or plastic guard designed to intercept a broken or derailed chain. Instead of striking the operator's hand, the chain should simply hit the chain catcher. Although the chain brake cannot stop the chain from hitting the operator at all, it can stop the chain from rotating as it hits the operator.
Anti-vibration handle systems
Even when they are lubricated well and used properly, chainsaws tend to vibrate a great deal. Excessive vibration can cause a variety of injuries to the operator, including white finger and hand-arm vibration syndrome. To reduce the stress this vibration places on the user's hands, modern chainsaws separate the actual cutting portion of the device from the handle and controls using a mounting system. Some chainsaws use metal springs to prevent vibration from reaching the operator, while others use rubber bushes.
