A Midsummer's Sharpening: How to Sharpen your Lawn Mower Blade

Image Gallery The sharpness of a lawn mower blade affects performance of the machine and appearance of the lawn. ISTOCKPHOTO/CHAD TRUEMPER

Sharpening your lawn mower blade is part of routine maintenance. It’s less complicated than you might think, and you’ll only need a few simple tools. If the tips of grass look ragged and brown after you mow, the problem may be a dull mower blade. Instead of being neatly cut, the grass is beaten to pieces.

Before you begin this project, think about safety. Just like when you pull the starting cord, moving the blade turns the engine, which could start. Disconnect the wire from the spark plug to avoid an unintentional start. It’s a good idea to wear leather gloves when removing the blade, but don’t try to hold the blade with one hand while working a wrench with the other. Instead, wedge the blade against a 2-by-4 to prevent it from turning while you remove the nut that keeps it in place. Before you start sharpening the blade, clamp it securely in a vice.

Choose the Right Tool

There are several tools you can use for sharpening the blade: a file, a bench grinder or a hand-held grinder. Electric grinders are available at most hardware stores for under $70. They will likely remove too much blade quickly, and they usually grind a concave edge, which will become dull sooner and is weaker than a V-shaped edge. The heat produced by a rapidly turning grinder can also weaken the blade. If you choose to use a grinder, dip the blade in water frequently during the sharpening process, and dry it each time before proceeding. This will cool the metal to reduce overheating and weakening.

A coarse-toothed file is probably the best choice. You can find one for under $10 usually. They’re easy to use, especially if you’re uncomfortable with power tools. Run the file toward the sharp edge of the blade. It removes material as you push it (not when you pull it back). Lift the file after each stroke; don’t “saw” with it. Follow the same angle as you see on the blade, and don’t sharpen the flat side. But you should run the file lightly over the flat side to remove the “burr” that forms as you sharpen.