Sharpen A Lawn Mower Blade

You can sharpen a mower blade with a file, a rotary tool or a bench grinder, but an angle grinder makes it fast and easy.

First, disconnect the spark plug wire (Photo 1). Next, seal the gas cap vent hole by putting a piece of plastic under the gas cap. Tip the mower with the carburetor facing up.

Clamp a 2x4 block to the mower deck to keep the blade from turning while you loosen it. Mark the “grass side” of the blade so you don’t reinstall it upside down. Loosen the blade nut (Photo 2). If it’s stubborn, use a breaker bar, or soak it with penetrating oil for a half hour and try again.

Clamp the blade securely in a vise or to your workbench. Wear gloves, a face shield, hearing protection, and a long-sleeve shirt. Before you start grinding, hold the grinder against the blade and tip it to match the blade’s bevel. Maintain this angle as you grind. Keep the grinder moving, using only light pressure so you don’t overheat the blade or grind off too much (Photo 3). If you overheat the metal, it’ll turn dark blue or black and become brittle, and it won’t hold an edge. Remove any nicks and dents and create an edge that’s about as sharp as a butter knife. A razor-sharp edge dulls quickly and chips easily.

Make several passes across the edge with the grinder, checking your progress frequently. Don’t grind off more than necessary. If your blade has a lot of nicks and gouges, start by holding the grinder at a right angle to the blade and grinding the edge of the blade flat to remove the nicks. Use light pressure and move quickly. It’s easy to burn the thin edge. After you’ve removed the nicks, go back to grinding at the correct blade angle.