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.
Buying a Chainsaw
As with every other thing you want to purchase, there are several questions you will have to ask yourself if you are shopping for a chainsaw.
• What do I need it for?
• What kind of trees will I be cutting?
• How big and how tall are the trees I will be cutting?
• Where will I be doing most of my cutting work?
The answers to these basic questions will go a long way into determining the type of chainsaw that you need. If you plan on using your chainsaw to cut hard wood, you will want one that packs more power. The diameter of the trees or wood you intend to work on will determine the length of the guide bar. If your work will take you to the woods you will need a gasoline-fed chainsaw.
There are three ways to power up a chainsaw: through gasoline, alternating current (AC), and direct current (DC). A gasoline-fed equipment is generally more powerful than either AC or DC power supplied. Thus, if you plan to use your chainsaw to cut oak, beech, or maple trees, you want this model. You will, however, have to mix gasoline and oil as their engines are usually of the two-stroke type. Note that even among the gasoline-fed versions, power output may still vary because of differences in engine displacement. The higher the displacement, the more power there is. Keep in mind, though, more power entails more difficulty in handling the chainsaw.
For softwood, such as pine, spruce, and hemlock, either AC- or DC-powered chainsaw will work fine. They also have the advantage of being more lightweight, quiet, and easier to handle. Starting the engine is a breeze as you will not need to jerk on a cord as you would in some gasoline-fed models. A disadvantage of the AC-powered chainsaw, however, is that its power cord limits your mobility.
The guide bar upon which the chain is mounted determines the maximum diameter your chainsaw can cut in a single pass. For a home-use chainsaw, a guide bar length of 14 to 20 inches will usually suffice. Professional users might want to go beyond 20 inches because they have to work with wood of large diameters. This increase in length, however, renders the machine more difficult to handle. Keep in mind that a guide bar can cut a log whose diameter is two times the bar’s length. A 14-inch bar, for instance, can cut a log with a 28-inch diameter if the cut is made around the log.
You might want to work on tree branches that are just barely beyond your reach. In this case, you will want a pole chainsaw. This tool has an extended handle that allows the user to extend his reach for up to 12 feet. A pole chainsaw may be gasoline-fed, AC- or DC-powered.
For those who will be doing most of their work in the forests where there are no electrical outlets to plug machines and battery chargers into, a gasoline-fed chainsaw is a must.
