Lawnmower blades are made of metal and feature sharp bevelled edges at each end. Over time, the bevelled edges, which make contact with grass, sticks, stones and other natural elements, may become dull. A lawnmower with dull blades can't make clean cuts and may lose rotation speed. Sharpen the blades' bevelled edges at home using an angle grinder. An angle grinder is a hand-held tool featuring an interchangeable wheel, which can be adjusted to grind metal materials such as lawnmower blades.
Pull the spark plug wire off of the top of the spark plug to prevent any start-ups. Flip the lawnmower on its side with the fuel filter facing up to expose the cutting blade. Mark the bottom of the lawnmower blade with a crayon or marker so you know what side is the bottom.
Attach an adjustable wrench to the nut, which is located at the centre of the cutting blade, and remove it. Catch any washers that may accompany the nut with your hand and place them to the side.
Find a flat work surface, such as a work bench or saw horse, to set the blade on. When the blade is on the flat surface, make sure that the mark you made representing the bottom is facing down and the blade's bevelled end is facing up. Secure the blade, with one of its ends protruding out, using either a bench vice or hand-held C-clamps so you can operate the angle grinder without any obstructions.
Equip the angle grinder with a grinding wheel that is designed for use with metal materials. Check the tool for any defects, such as a damaged cord, cracked casing or missing safety features, which could hinder its use. Squeeze the angle grinder's power trigger to bring the grinding wheel to full rpms.
Hold the angle grinder so that the grinding wheel closely matches the mower blade's bevelled edge. Glide the rotating grinder wheel gently over the bevelled edge, working form one end to the other. Avoid pressing down hard, over-angling the grinding wheel or stopping on one spot for any length of time, which could make the cutting blade unbalanced.
When one side of the mower blade is complete, turn it around and secure it with the vice or C-clamps. Sharpen the blade's bevelled edge with the angle grinder, making sure to match the opposite side.
Place the blade back onto the spindle located at the bottom of the lawnmower with the mark that represents the bottom of the blade facing down. Reattach the nut and any accompanying washers to the centre of the blade using the adjustable wrench. Turn the mower over and reattach the spark plug wire.
Sharpen the lawnmower's blades after the machine runs out of gas, which will prevent gas from leaking out when the mower is flipped on its side. You can also use a siphon to remove the gas before flipping the mower.