A lawnmower will ruin the yard if the blades are not properly sharpened. Blades that are dull will rip at the grass as opposed to cutting it, weakening the grass and causing disease. Mower blades that have large dents or nicks in the blade should not be sharpened, but replaced instead. When sharpening, it is important that the blade is balanced after the sharpening. A blade that does not have an evenly distributed weight will cause wear on the engine and reduce efficiency.
Pull out the spark plug from the engine to keep it from starting.
Flip the mower onto its side, with the gas tank below the carburettor.
Place a piece of wood at the bottom of the mower deck and lodge the blade into it.
Remove the nut holding the blade in place using a wrench. Hit the wrench gently with a rubber mallet to remove the nut if it is stuck. Wear gloves to prevent injury to the hands.
Place the blade into a vice to hold it in place. Put on your gloves and a face shield to protect yourself from sparks.
Turn on your grinder and run it smoothly across the blade. Do not press down hard. This damages the blade. Make two passes and check the blade. Allow the blade to cool to prevent it from becoming brittle.
Set your blade on a blade balancing cone. Grind metal off whatever end tips down toward the table top. Remove a small amount at a time.