Gasoline and electric lawn mowers use a rotary blade underneath the blade housing to cut the grass. The blade is essentially a long piece of flat iron with the last 4 inches on each side of the leading edge ground to a sharpened point. The trailing edge behind each cutting surface is folded upwards, to force the grass out of the grass chute. If the blade becomes dull or dinged, you can sharpen and balance the blade with a bench grinder and a DIY lawnmower blade sharpener jig.
Disconnect the mower's spark plug wire from the spark plug, and remove the lawn mower blade from the drive shaft.
Place one edge of the lawnmower blade against the grinding wheel of a bench grinder (one that is turned off), and adjust the angle of the tool rest until the beveled cutting edge of the blade is resting flat against the grinder. Tighten the lock nut on the tool rest to lock the rest in place.
Put on work gloves and safety goggles. Turn on the grinder, and hold the blade flat on the tool rest, grinding the cutting edge at the correct angle. Move the blade back and forth against the grinding wheel, grinding in 2-3 second increments. Avoid long stretches of grinding, as this will heat up the blade, causing it to lose its tempering and weakening the steel. Dip the blade in a pail of cool water if it becomes too hot between grindings.
Flip the blade over, and grind the opposite cutting bevel in the same manner.
Place a piece of angle iron on a work table, with one edge facing upward to serve as a sharpener balancing jig. Balance the blade on the edge of the angle iron, with the center of the mounting hole directly over the edge of the angle iron. Notice if the blade tilts to one side of the other. If it isn't perfectly balanced, re-grind the heavier edge until the blade is perfectly balanced.
Things You Will Need
- Bench grinder with adjustable tool rest
- 6-inch length of 1-inch-by-1-inch angle iron
- Leather work gloves
- Safety glasses
- Pail of cool water
- Always wear gloves and safety glasses when using a bench grinder.