Sharpening the blade of your lawn mower is a basic and essential maintenance task. If the blade grows dull or has nicks from hitting rocks and fallen tree branches, it won't cut the grass evenly, and will only rip it instead. Sharpen the blade yourself, with your choice of different, effective tools such as a file, bench grinder or a belt sander.
A metal file is the most basic tool to use for mower blade sharpening. If the blade exhibits only smaller nicks and you observe that the edges need to be sharpened, use a file to even out the blade's rough spots. Work the file in the direction of the angle that the blade's edge already has. Use a fine file to create an even smoother finish to the blade surface.
A bench grinder is an essential tool in shops for removing nicks and restoring the angle on beveled, metal cutting tools, such as a lawn mower blade. The electric-powered bench grinder uses two large grinding wheels, and is mounted on either the end of a workbench, or on a stand. This tool is used when the nicks and damage to the blade are greater than a metal file can handle. Remove the blade from the mower, and be sure to wear work gloves and safety glasses while using the bench grinder.
A portable belt sander is a power hand tool, using a loop of sandpaper, to sand away blade nicks and sharpen the edges. To initially remove the blade's imperfections, install a medium-grit sanding belt on the tool, and finish up the sharpening with a finer-grit belt. As with the other tools, follow the angle and contour of the blade's edge with the belt sander when sharpening.
Sharpen the mower blade each time the grass exhibits signs that the blade is dull, such as when the grass looks torn instead of properly groomed. Before removing the lawn mower blade, remove any battery or spark plug wire, depending on which one the mower has. After sharpening the blade, make sure that it is correctly balanced before you put it back on, or the mower will vibrate excessively. Also, clean all the collected dirt and grass clippings from the underside of the mower.