Push-style lawn mowers use a very fast rotating blade to cut your lawn. The sharp edge of the blade slices right through the grass blade. After frequent mowing, the blade begins to slowly dull. If you run over sticks and small stones, the blade dulls at a quicker rate. When the blade dulls, the quality of the cut on the grass decreases rapidly, and eventually instead of cutting the grass, it shreds the grass blades. The shredded grass blades allow easy entry of disease and fungus into the grass. Sharpen the blades on a push mower before each grass cutting season to ensure your grass gets the proper cut.
Turn off the power to the push mower, and disconnect the spark plug cable.
Lay the push mower on its side, and wedge a length of two by four board in between the blade and the mower housing.
Use an adjustable wrench, and remove the push mower blade by loosening and removing the bolt that holds the blade to the engine shaft.
Place the blade in a table vice to keep it from slipping as you work.
Sharpen the blade with an angle grinder or metal file. Follow the blade's shape and contour. You don't want to remove a ton of material; you're looking for a nice clean and sharp edge.
Balance your push mower blade. Position your blade on the plastic balancer. You want the blade to sit almost perfectly level on the balancer. If one end dips down, file or grind a little more steel from that end.
Put the push mower blade back on the lawn mower. Tighten it down, and remove the two by four board.
Set your push mower upright, and reconnect the spark plug cable. Start the push mower up, and make sure that there is no vibrating or rattling coming from the blade.