Inside a Chain Saw
Mechanism of Chain Saw
Chain saws make life a lot easier for those who have to cut trees. Their engine casings are often just about a foot in width, length, and depth. The length of the guide bar varies from 14 to 36 inches. On average, a chain saw weighs about seven kilograms (15 pounds). Yet with these relatively small measurements, it packs a lot of punch. What is it that makes a chain saw so powerful?
At the heart of chain saws are two-stroke gasoline-fed engines consisting of a cylinder, crankshaft, piston, and connecting rod. Often, these come with a displacement of about 50 cc (3 cubic inches). This 1.8-kilogram (4 pounds) power plant can generate as much as three horsepower.
To keep the weight of chain saws to a minimum, they are not equipped with an electric starter. Instead, you will have to crank them with pull starters. As these are two-stroke engines, a mixture of gas, oil, and air from the carburetor is needed to fuel them up. An air intake manifold collects air while a fuel tank supplies the fuel. This mixture is drawn into the engine where it is burned by a spark plug connected to a magneto. The residue of this burning escapes through a spark arrestor/muffler. A small oil pump lubricates the engine, while it is cooled by the cooling fins that surround the combustion chamber. A separate oil container supplies chain-oil to the rotating chain to keep it running smoothly.
The power generated by the engine will not cut trees unless it is transferred to the chain which does the actual cutting. This is accomplished by the centrifugal clutch which consists of an outer drum, a center shaft, and a pair of cylindrical weights attached to the shaft.
The outer drum is free turning. Incorporated with it is a sprocket that engages and turns the chain. The moment it moves, the chain follows.
The center shaft can be thought of as an extension of the crankshaft that protrudes out of the engine block. Starting the engine rotates the crankshaft, and thus also the center shaft.
The cylindrical clutch weights are connected to the center shaft in such a way that they spin as a unit. The weights are pushed against the shaft by springs. This is their position if the engine is merely idling. However, if it is powered up, the increased rotations of the crank and center shafts provide enough centrifugal force on the weights allowing them to push the springs back. They come into contact with the outer drum, thus spinning it, transferring the power from the engine to the cutting chain.
