A well-sharpened lawn mower blade will make cleaner cuts in your grass. Dull blades can tear, rather than cut on your grass and, as such, create more trauma on the individual grass plants. Cleaner cuts help ensure a healthier, fuller lawn. The curves on mulching lawn mower blades make sharpening them a little more difficult than sharpening more traditional, straight blades. With the right tools and processes, sharpening a mulching mower blade is not difficult.
Disconnect the spark plug wire from the spark plug on gasoline-powered mowers. If your lawn mower is electric, make sure it is unplugged from the wall. For battery-powered lawn mowers, follow the manufacturer's instructions to disconnect the battery from the motor.
Turn the lawn mower on its side. If your mower is gasoline powered, make sure the air filter and carburetor are facing up to prevent gasoline from leaking out.
Wedge a board between the mower deck and the blade to keep the blade from rotating as you remove the center bolt on the blade.
Mark the bottom side of the blade with spray paint or an indelible marker. A common mistake when re-installing the blade is to put it on upside down. Placing the blade on upside down will prevent the blade from cutting properly.
Loosen the blade fastener with a long-handled wrench. The fastener may be very tight. Using a long-handled wrench will allow you to apply more force when removing the fastener.
Remove the blade and place it securely in a vice.
Examine the original angle of the cutting edge. It is important to keep the cutting edge at the original angle.
Sharpen the cutting edge of the blade with metal files. Mulching blades are often curved and may require more than one type and shape of file. Sharpen the blade until it is about as sharp as a common household butter knife.
Reverse the blade in the vice and sharpen the other side of the blade.
Remove the blade from the vice and re-attach the blade to the mower. Replace the wood that prevents the blade from turning and attach the blade fastener as tightly as possible.
Remove the wood block and re-attach the spark plug wire.