A lawn mower blade sharpener is an accessory that is used to keep a lawn mower functioning properly. Lawn mower blades, like all metal blades, need periodic sharpening to keep working at maximum efficiency. The best results come with using a quality bench grinder or professional blade grinder as a lawn mower blade sharpener.
The removal of the lawn mower blade is the trickiest part of the sharpening process. To start, remove the spark plug wire to prevent the mower from starting accidentally, and then squirt the blade bolt and nut with penetrating oil. Use a blade holder to keep the blade still while removing the nut, and scrape off excess grass and dirt around the middle hole in the blade prior to using the lawn mower blade sharpener.
Maintaining the correct angle of the blade is most important while sharpening. The owner's manual for the lawn mower blade sharpener will show the exact angle where the blade should be, but it is typically 40 degrees. A blunt angle will lessen the quality of the cut, and a sharper angle will dull and damage the blade sooner. If possible use a milled edge sharpener. It will provide the best cut. A sharpener with a grinding wheel will leave a hollow grind and is not recommended for use as a lawn mower blade sharpener.
The blade should be moved back and forth across the grinder at the correct angle for the mower. If the blade is forced into the grinder it will heat up and lose some of its hardness. A blade does not need to have all its nicks removed by the sharpener. A few nicks are tolerable, but if it is very damaged, it may need replacing.
A blade balancer can detect whether or not the edges of the blade have been evenly sharpened. A wall-mounted balancer may be preferred, but a more inexpensive option is a cone-shaped blade balancer. This step is important because a bent or unevenly ground blade can damage the mower. A moderately bent blade may be able to be corrected by grinding more metal off the heavy end of the blade. If it is seriously bent it is better to replace the blade as it can break off while in use and cause injury.
After the blade is balanced any jagged edges can be removed with a metal file. Replace the blade on the mower deck and attach with the nut and bolt. Keep in mind that the blade will now be significantly sharper than it was upon removal and should be handled with caution.