Many homeowners neglect sharpening hand mower blades. They're unaware that a sharp blade means a greener, fuller, and healthier lawn. A dull blade might destroy the lawn. It results in a weaker lawn prone to fungal growth and other grass diseases. Sharp blades cut cleanly, which mean less stress on the mower and the person doing the mowing.
Remove the sparkplug wire. If your mower is battery-operated, remove the battery. On gas mowers, locate the carburetor and air filter. You'll recognize the carburetor by the throttle cables running to it. When you tip the lawn mower to get to the blade, keep the carburetor side up, or at the top. This prevents a smoke cloud from leaking oil the next time you start it. If your mower has a gas cap with holes in it, work outside so gas doesn't leak onto your garage floor, or keep rags ready to wipe up drips.
Tip the lawn mower on its side, and look for a single bolt or nut holding the blade in place.To clamp the blade, wedge the short two-by-four between the blade and deck. Loosen the bolt or nut with the long-handle wrench. Turn it counterclockwise. Remove the bolt and blade.
Mark the blade with spray paint before removing it, so you don't install it upside-down. It won't cut that way. After removing the blade, check to see if it needs replacing. Chips, thinning and bends are all signs that the blade needs replacing.
Secure the blade in a vise. Using a "mill bastard" file (name refers to how fine its teeth are cut), sharpen the cutting edge until the sharpness feels like a butter knife. The file cuts in one direction only, which is on the push stroke. Refrain from making the blade razor-sharp, as this causes it to dull faster.
Insert the two-by-four in the reverse direction and hand-tighten the bolt. Bear down on the breaker bar to tighten the bolt.