How to Sharpen a Chainsaw Chain
By Dave Boyt | Oct 6, 2015
Chainsawing: Is it art, or science … or magic? The feel of a good, sharp chain sinking down through an oak log spewing a steady spray of chips certainly feels magical, especially when the saw is perfectly tuned. But if the only time you experience this magic is with a new chain, maybe it is time to tune up your sharpening skills as well.
Actually, there is no magic to it … just science, and a little math – geometry, to be precise – and precise it must be. The actual cutting takes place at the tip of the blade, so it must be perfectly formed. The rest of each tooth removes the chip of wood so the next tooth can do its work, and so on. Those links between the teeth also play a vital role. These “rakers” control how much of a bite the cutting teeth can take. As the cutting teeth are filed shorter, the rakers need to be filed lower.
Understand the lingo
The first order of business is to make sure you have the right chain for your saw, skill level, and job at hand. Most of the information you need is stamped right on the bar, if you know where to look. The drive links – the part of the tooth that engages the bar and bar sprocket – need the right spacing, or “pitch,” so they will go smoothly around the sprockets. The most common pitches are 0.325 inches and 0.375 inches (3⁄8-inch). The drive links must also be the correct thickness, or “gauge,” to match the width of the groove in the bar. Too big, and the drive links will not fit. If the gauge is too small, the chain will wobble and will not cut straight. This also puts excessive wear on the bar and chain, making the problem worse. The gauge is stamped on the bar, and will be 0.043, 0.050, 0.058 or 0.063. Larger saws tend to use the larger gauge chains, because they are subjected to more stress. The bar will also have the number of drive links stamped on it. With these numbers, you can go into any chainsaw shop and be confident of getting a chain that will fit. If in doubt, bring along the bar or an old chain.
At the shop, you will be presented with more choices: full comp, semi-skip, or skip tooth? Chisel point or semi-chisel? Safety chain or “professional”? Let’s take a minute to decipher these terms.
“Full comp” means that all the cutting teeth are present. This is the most common for general cutting. If you are using a long bar, you might consider semi-skip, which has two teeth, then skips a tooth, or full skip, which has half as many teeth as a full comp chain. These chains are slower and rougher cutting, but have less tendency to bog down the saw in big logs, and have fewer teeth to sharpen – a good thing when your bar has 84 drive links. I use a semi-skip tooth chain on a 24-inch bar with my 65cc chainsaw for those times when I need just a little more reach to get through a big tree or log.
Chisel point teeth come to a sharp point, while semi-chisel are slightly rounded. The chisel point cuts much faster and smoother, but must be kept razor sharp to maintain this advantage. Semi-chisel teeth last longer, especially in dirty logs or in situations where you might put the chain in the dirt once in a while. Properly sharpened, they cut well, but not as smoothly as chisel chains.
Finally, the decision of whether to use a “safety chain” is up to you. It does effectively reduce the chance of kickback – the No. 1 cause of chainsaw injuries – but there are a couple of trade-offs. The rakers cannot be filed, so the chain has a limited number of sharpenings. Also, you will not be able to use the tip of the saw to make bore cuts into the wood. This is an advanced technique, and you may not miss it for occasional trimming and firewood jobs.
If you want the “professional” chain, you may need to ask for it specifically, and you should understand the warning on the box about the hazards of using this chain.
Eventually your new chain will lose its edge, and you will find yourself working harder and harder to force it through a log. Those nice clean shavings become powder – instead of chips flying, you’ll see smaller particles of wood coming out of the cut as you jam the saw spurs into the log for more leverage. The chain heats up, causing it to loosen, and your arms ache as you try to make those last few cuts. Finally, you are forced to give up and put on a fresh chain, or sharpen the one on the saw. Sawing with a dull chain puts unnecessary wear on the equipment, and may put you at greater risk as well. Rule No. 1 of chainsaw sharpening: Instead of sharpening a dull chain, put a razor edge on an already sharp chain. Sharpening the chain at the first signs of diminished performance takes only a few minutes, and keeps the chips and sawdust flying. It also saves gas and oil, and wear on the machine.
Tools are simple. At the minimum, you should have the “scrench” (screwdriver/wrench) and appropriate-size round file. In addition, I keep a stump vise, file guide, flat file, and a red Sharpie pen in the box. While I use only the file to restore the edge to the chain, the other tools come in handy when I need to do major sharpening after hitting a rock or putting the chain into the dirt.
Adjust the tension of the chain first. This keeps the chain from moving while you sharpen. It is normal for a new chain to stretch a bit, and if you try to muscle a dull chain through a log, it will stretch even more. Follow the procedure as described in the chainsaw manual. Generally, it works best to hold the handle and rest the tip of the bar on a piece of wood as you tighten it. Tighten the adjusting screw until the chain comes into contact with the bar on the bottom side. The chains shouldn’t sag, but you should also be able to move the chain around the bar with your hand. After tightening the bar nuts, move the chain all the way around by hand to make sure it spins smoothly without sagging or binding.
The correct file size should be printed on the chain packaging, or ask the dealer. Avoid the temptation to hold the file by the tang—get a proper handle so you can control it and stroke the file its full length for a straight edge on the tooth. The stump vise holds the nose of the saw securely, enabling you to use both hands for filing. The Sharpie is the next tool out of the box. Use it to mark the first tooth you file, so you will know when you have sharpened all the way around the chain.
How much filing should you do? One school of thought is to file the same number of strokes for each tooth. In theory, this keeps all teeth the same length. In fact, there will be some variation, especially between the two sides of the chain. The good news is that as long as the rakers allow the teeth to cut the same depth, it doesn’t matter.
When hand filing, watch for that sliver of shiny metal on the tip of the tooth to disappear, then move on to the next tooth. Be sure to maintain the angle of the tooth so the geometry is consistent. For a touch-up, this is easy to do, but after several touch-ups, or after dulling the chain in dirt, rock or metal, use the file guide to get it back in shape. The guide also gives you the right depth for the “gullet,” which is important for removing the chips from the cut. Use one hand to do the actual filing and the other to control the tip so the file cuts in a straight line. If the sharp chain doesn’t cut quite as aggressively as it should, or tries to cut in a curve, use the flat file and raker guide to bring the rakers down to the same height relative to the cutters.
If you do everything perfectly, your chain will cut as well or even better than a new one. Sometimes, no matter how much you fuss over a chain, it still will not cut as it should. Swallow your pride and take it to a chainsaw shop. The sharpener will get all the teeth the same length and the rakers the same height. For about a quarter of the cost of a new chain, it will cut like it just came out of the box. And if you take in the chain itself, already removed from the saw, sharpening often comes at a reasonable cost.
The number of sharpenings you get depends on how well you maintain the chain. Generally, I use a chain until the back edge of the teeth are worn away. Even if you have all the sharpening gear, bringing a spare chain may make the difference between a full day of cutting or going home early with the job unfinished. If you hit a nail or rock that does major damage to the chain, you can often save time by putting on a fresh chain and dealing with the damaged one in the shop later.
Dave Boyt manages a family tree farm and operates a portable sawmill in southwest Missouri. He is a certified Master Logger and has cut all the firewood to heat his home for more than 30 years.
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