How to Sharpen a Lawn Mower Blade

It’s easy to tell when the blade on your lawn mower is dull: the tips of the grass blades are tattered and brown. You can sharpen the blade yourself, or take it to a hardware store to have it sharpened. To sharpen it yourself, safely, follow these steps:

1. If you have a gas powered mower, disconnect the spark plug wire. Carefully tilt the lawn mower on its side with the fuel tank's fill hole facing up.
2. Put on work gloves to protect your hands from being cut. To immobilize the blade, wedge a wood block between the blade and a solid area of the mower housing.
3. Remove the bolt and washer, and inspect the bolt. If it’s damaged, replace it with one the manufacturer approves, rather than a standard bolt (you can order it from Sears PartsDirect). Blade bolts often are specially designed and heat-treated to prevent failure. Any failure of the blade assembly during use could throw a blade and cause a lot of damage.
4. Remove and inspect the blade. If it’s bent, dented or badly chipped, get a manufacturer-approved replacement. A damaged blade cuts grass poorly and can make the mower vibrate excessively.
5. Secure the blade in a vise and sharpen the blade with a file, or sharpen it on a bench grinder. Follow the existing angle of the cutting edge and, if using a file, file in only one direction.
6. After sharpening, check that the blade is balanced. Drive a finish or casing nail into a wall and hang the blade horizontally, through the center hole. If one end dips, grind more from that end.
7. Use a torque wrench to reattach the blade, tightening the bolt to the torque specified in the owner’s manual — most blade bolts require around 45 to 55 foot-pounds of torque.
8. Reinstall the spark plug.