Sharpen a chain saw

To understand how to sharpen a chain saw, you must have a basic understanding of the entire mechanism. To simply sharpen the chain without adjusting pitch or understanding gauge, for example, may cause safety concerns for you and lead to potential damage of the saw. Likewise, if you don't know how to use a round file or depth gauge, you may not correctly sharpen the chain.

Chain components and types Each component of a saw chain performs a specific function (see Figure 3, page 24). The tie strap connects the cutters and provides a surface on which the chain rides. It also provides an anti-kick back guard for the chain. The drive chain provides a curved point, which the sprocket drives, and rides in the bar groove. The right- and left-hand cutters have specific names for their parts (see Figure 2, page 24). The gauge and pitch of the chain determine the chain size. The pitch is the distance between every other rivet divided by 2, and the gauge is determined by the thickness of the drive link.

Types of chain When buying chain, always refer to the pitch, gauge and number of links needed for the size of the bar. In addition to the size of the chain, the type of chain also is important because this determines the types of jobs the chain saw can perform.

The two major types of chain are chipper and chisel. The chipper chain has a curved working corner, and the chisel chain has an angled working corner. In addition, the chains may include small cutters between a chisel and a chipper with a slightly rounded corner. When this is the case, the chains are called semi- or micro-chisel chains.

Chain-saw chains have the ability to cut due to their working corner (see Figure 2, page 24). The sharper the angle of the working corner, the faster the chain will cut. The more curved the working corner, the longer the chain remains sharp. Therefore, you must determine how you will use the saw and select the appropriate chain. For example, if your saw is used in an environment where the chain is exposed to some dust and dirt, a chipper chain is your best choice.

How a chain cutter works When sharpening a chain-saw cutter, you must understand how the cutter tooth works. This also will help you understand the different types of chain. Cutting consists of three steps: * As the cutter enters the wood, the depth gauge rides on the bottom of the wood, which determines the size of the bite or chip removed. * The working corner of the cutter tooth cuts across the grain of the wood and does most of the actual work. * The top-plate cutting angle lifts out the chip of wood much like a chisel.

Sharpening the chain A chain saw renders unsatisfactory results if you do not properly maintain and sharpen its chain. Before sharpening, tension the chain on the bar so that it is firm when cutting into a piece of wood. Make sure the teeth are clean and do not have oil on them. This makes filing more effective. You'll need a few tools for sharpening a chain. More-costly, motorized chain-grinding equipment exists, but you don't need it to achieve a sharp chain.

A file holder, round file, flat file and depth-gauge tool are all that you need. The correct size of file to use is determined by the size of the chain (see table, page 24).

Here are the important steps to follow when sharpening the chain.

* File the depth gauges to the correct height. The file holder correctly sets the file height by resting on the depth gauge. Setting the depth gauge or joint clearance is dependent on the size of the chain. Take note that the depth, or clearance, is based on normal operating conditions. You can slightly change these depths depending on cutting conditions. For example, if you are cutting hardwood in cold temperatures (belowfreezing), the clearance may need reduction. Conversely, if cutting softwood, the clearance may be increased. This is important because a setting that is too low increases the possibility of kickback and vibration as well as overworks the saw. An overly high setting causes the saw to remove chips that are too small to be productive. * File the front corner of the depth gauge. Once you file the depth gauge to the correct height, the front corner will need filing to maintain a proper radius. This reduces friction and the chance of kickback. * File the top-plate to the correct angle. Hold the file at the correct top-plate angle. Most holders have a 30- and 35-degree angle scribed on the top of them. * File the side-plate angle. For a 90-degree side-plate angle, hold the file parallel with the top of the chain. For an 80 to 85-degree angle, tip the file slightly downward. * Check the cutting angle. The last angle, the cutting angle, forms automatically when the top- and side-plate angles are correct. It is usually 60 degrees. These are the most common angles for the most popular types of chain (See Figure 1, page 22).

Chain maintenance To keep the chain in good condition, you must tension it correctly and keep it well-lubricated. Improperly tensioned chains damage themselves as well as the drive sprocket and bar. A chain tensioned too tightly prematurely wears out the chain and the bar and may bend the crankshafts on smaller (18 inches or less) saws. Typically, this occurs when the tension is too tight while the chain is still warm. As it cools, it may shrink enough to bend the crankshaft.

Loose tension causes the chain to thrash and beat on the bar. In addition, when the chain is too loose, it may come off, causing damage to the chain, bar and-more importantly-inviting injury to you.

Michael McCaskey is a professor at the State University of New York (Cobleskill, N.Y.).

* Always file from the inside out, putting slight pressure on the forward stroke only. Make sure that the file contacts the entire cutting edge with each stroke. * Keep all cutters the same length. This keeps the depth-gauge clearance uniform. Otherwise, the chain cuts toward the side that has the longer teeth. * Always try to prevent the chain from hitting dirt, rocks or metal. This quickly dulls and chips the teeth. * File the cutters to remove damage from the cutting edges. * Clean the gullet after every fifth sharpening of the chain. A clean gullet opens the area for chip removal which, in turn, allows for better side-plate cutting action.

* Always tension the chain when the bar and chain are cool. Keep in mind that breaking in a new chain saw (chain-run-in) also is important because a new chain stretches more than an old one. Run the saw with a new chain under light cutting conditions and frequently check the chain for correct tension. * Store extra chains in an oil or diesel-fuel bath to keep them well lubricated. * Use bar oil to lubricate chains. Do not use old or dirty engine oil. * Make sure the automatic oilers are working by pointing the saw toward a fresh cut and watching for oil drops hitting the wood or for an oil stain. It is especially important to put extra oil on the chain before and after cutting.

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