Lawn mowers use rapidly spinning rotary blades to cut the grass. As the blade continually shears through grass blades, it slowly dulls over time. Also if the blade comes in contact with sticks or rocks, it will become dull quicker. You should sharpen lawn mower blades yearly to properly maintain your lawn mower and keep your lawn healthy. Sharpening lawn mower blades is a task that the typical homeowner can accomplish. Only a few tools are required.
Turn the lawn mower off, and disconnect the spark plug. A cable should be attached to the spark plug that just pulls off.
Turn the lawn mower on its side, and wedge a piece of 2x4 in between the mower blade and the mower deck housing.
Use an adjustable wrench to loosen the bolt that holds the lawn mower to the engine shaft. Unscrew it all the way, and set it and the washers aside.
Remove the lawn mower blade, take to your table vice and clamp it down.
Remove any rust with a steel brush. Take a file or angle grinder, and sharpen the blade. Follow the contour of the blade edge, and make a nice, smooth edge on the blade.
Remove the blade from the vice and support it in the center. Check if it tips toward either direction. If it does, the blade isn't balanced properly. Remove a little more metal on the side that tips down and check again. Keep repeating until the blade is perfectly balanced.
Bolt the blade back onto the lawn mower, and tighten the bolt down with your wrench.
Position the lawn mower back upright, and reconnect the spark plug wire. Your lawn mower is now ready to mow grass again.