Sharpen Your Chainsaw: Three "Tried-and-True" Methods

by Joseph Truini

The chainsaw is arguably the greatest time and labor-saving power tool ever invented, especially when compared to its predecessor, the axe. But even the largest, most powerful chainsaw won't cut with a dull saw chain. The good news is that unlike most other power cutting tools, you can sharpen a chainsaw to like-new condition in just a few minutes.   

Here, I'll discuss three do-it-yourself options for sharpening a chainsaw, starting with the simplest method: using a file. Then, for those looking for a faster, easier way, I'll show two power tools specifically designed for chainsaw sharpening.

However, before getting into specific sharpening techniques, let's take a quick look at how you can tell if your chainsaw is dull.

Signs of a Dull Chain

Chainsaws are so powerful and cut so aggressively that it's not always obvious when the saw chain needs sharpening. A sharp chainsaw cuts smoothly and quickly with little effort. The first sign of dulling is when the saw cuts noticeably slower. The next indication is when you must apply excessive pressure to force the saw through the cut. As the chain continues to get duller, the more slowly it cuts and the more pressure you must apply. That not only puts undue stress on the saw motor, but it could cause the saw to kick back toward the user.

Here's another telltale sign that your chainsaw needs sharpening: Examine the wood being expelled by the saw. A sharp chainsaw sprays out thin shavings. A dull saw spews out fine wood dust.

In ideal conditions, a chainsaw can remain sharp for four to six hours, even longer in some cases. However, it can become dull in less than 10 minutes when cutting dirt-covered logs or wood that's extremely hard or dry. When slicing up a felled tree, be careful not to let the tip of the bar hit the ground. Nothing dulls a chainsaw faster than sawing into dirt and rocks. And if you notice that the saw chain has cutting teeth that are badly nicked, bent or missing, replace it with a brand new saw chain.

Now let's talk about how to sharpen a dull saw chain.

Method 1 - Sharpen your chain with a hand file

Look closely at the saw chain, and you'll see a series of teeth with sharpened semicircular cutting edges. The diameter of the edges varies from one saw to the next, but is typically 5/32 inch, 3/16 in. or 7/32 in. To sharpen these curved edges, use an appropriate diameter round file. Also, notice that the tops of the cutting teeth are ground at alternating angles, meaning one tooth angles to the left, the next to the right.

In between each cutting tooth is a flat piece of metal that's shaped somewhat like a shark's dorsal fin. These pieces called, rakers, are slightly shorter in height than the cutting teeth. Rakers don't require sharpening; their purpose is to act as depth gauges to control how deeply the teeth cut into the wood. Without rakers, the teeth would cut much too aggressively for the saw motor—and user—to handle. 

As mentioned above, you can sharpen the saw chain with a round file, but to ensure consistent, accurate results, mount the file in a sharpening guide. The guide serves two purposes: It provides a flat surface for resting the file on the saw chain, and it controls the depth that the file can cut. Stamped into the top surface of the guide are angled lines that correspond to the pitch—or cutting angle—of the saw chain teeth. Sharpening guides are sold at most home-improvement stores for about $10; a two-pack of round files will cost another $7 or so.

Round file shown installed in a sharpening guide.

Before sharpening, you need two specifications: the diameter of the semi-circular cutting edges on the saw chain, and the pitch—or rake angle—of those cutting edges. Both pieces of information are available in the chainsaw owner's manual or by the manufacturer of the saw chain. Select a round file that matches the diameter of the semi-circular edges on the cutting teeth. Important: Be sure to use a round file, not a rat-tail file, which tapers across its length.

Once you're ready to get started, follow these steps:

  1. Loosen the thumbscrews on the sharpening guide and slide the round file beneath the two metal hold-down clamps. Tighten the screws to secure the file in the guide.
  2. Engage the chain brake and clamp the chainsaw's steel bar in a vise. Use an indelible marker to mark the first cutting tooth to be sharpened. This will act as a visual reminder to let you know where you started sharpening.
  3. Set the sharpening guide on top of the saw chain with the file resting against one of the semi-circular cutting edges. Adjust the guide until the angled lines stamped onto the top of the guide are parallel with the saw's steel bar.
  4. Now, while maintaining that angle, push the file forward across the cutting tooth.
  5. Repeat five or six more times, using slow, steady strokes. Keep count of how many strokes you make across the first tooth, and make the same number of filing strokes across all the other teeth. When properly sharpened, the entire curved cutting edge of the tooth should be clean and shiny.
  6. After sharpening the first tooth, skip the next one, and file the tooth after that. Remember, the sharpening angle on the saw teeth alternate to the left and right. Therefore, it's best to sharpen every other tooth, so you won't have to keep changing the filing angle back and forth.
  7. Continue in this manner, filing every other tooth, until you've worked your way back to the starting point on the saw chain.
  8. Now, move around to the other side of the bar, and start filing the teeth that you skipped on the first go-around.

File sharpening may feel awkward at first, but you'll get comfortable after awhile. Once you've perfected this technique, you'll be able to sharpen a chainsaw in less than 15 minutes.

Note that after the saw chain has been sharpened several times, the cutting teeth will eventually be at the same height or lower than the rakers. When that happens, the rakers will prevent the cutting teeth from reaching the wood. To regain a cutting edge, use a flat file with sharpening guide to file down the height of each raker.

This sharpening kit includes a handle, two guides, assorted round files and a flat file.

Method 2 - Use a portable power sharpener

A cordless rotary tool fitted with a cylindrical grinding stone
and sharpening guide provides a quick way to sharpen chainsaws.

Filing is fine, but power sharpening is quicker and much more fun. There are two types of portable power tools that make quick work of chainsaw sharpening. The first is a rotary tool, commonly called a Dremel tool, which accepts a chainsaw sharpening accessory. The accessory kit includes a cylindrical grinding stone and an alignment guide that clamps onto the tool. Note that rotary tools are available in both corded electric and cordless versions.

The second portable power tool option is an electric grinder that's specifically designed to do just one thing: sharpen chainsaws, which it does it very quickly and very well. The tool comes in kit form with various-size grinding stones and a metal sharpening guide that mounts onto the nose of the tool.

This portable electric grinder is specifically designed for sharpening chainsaws.
It includes three sizes of grinding stones to fit virtually any saw chain.

The rotary tool and the dedicated chainsaw sharpener both do an excellent job of sharpening saw chain. If you already own a rotary tool, then consider getting the sharpening accessory kit, which can also be used to sharpen lawnmower blades, grass shears, axes and other tools. Otherwise, the dedicated grinder is a smart investment, especially if you frequently sharpen your chainsaw.

Method 3 - Use a benchtop sharpener

Get consistent, professional results with a benchtop chainsaw sharpener.

If you use a chainsaw year-round, or if you own more than one chainsaw, then you can save a significant amount of time and energy by sharpening the saw chains with a bench-mounted sharpener. This style sharpener delivers most accurate, consistent results.

The tool operates a bit like a power miter saw, only instead of a woodcutting blade, it's equipped with a 4½-in.-diameter grinding wheel. The wheel tilts up to 35 degrees left and right to accommodate the most common saw-chain cutting angles. Here's how to file with one:

  1. Start by clamping or screwing the tool to your workbench.
  2. Next, remove the saw chain from the saw and set it into the tool's vice.
  3. Adjust the grinder to the proper angle.
  4. Squeeze the trigger and pull down on the upper handle until the spinning wheel contacts the cutting tooth on the saw chain. It only takes two or three seconds to sharpen the tooth.
  5. Release the clamp, reposition the saw chain and repeat.
  6. As with filing, sharpen every other tooth, then readjust the grinding angle and sharpen the remaining alternate-angle teeth.

A benchtop sharpener is certainly the quickest, most accurate way to sharpen a saw chain, but just as importantly it makes it nearly impossible to ruin a saw chain by grinding away too much material.

Regardless of which tool or technique you use, keep the saw chain sharp and your chainsaw will last longer, perform better and cut quicker and more safely.

About the author: DIY expert Joseph Truini writes for The Home Depot. He has also written several home improvement books. Joseph share his knowledge and experience on everything from how to use an electric chainsaw sharpener to building a composter.