How to Sharpen Rotary Cutter Blades

A walk-behind lawn mower uses a single rotary blade to cut grass and lift the clippings into a catcher or out onto the lawn.

A walk-behind or riding rotary lawn mower is typically powered by a gasoline or electric motor that spins the cutting blade at a high speed underneath the mower deck. This spinning blade not only cuts the grass, but lifts the clippings through a chute and either out onto the lawn or into a catcher. The rotary blade can become dulled by hitting foreign objects, but you can sharpen rotary cutter blades with a bench grinder and a tool rest.

Things You'll Need

• Socket set
• Bench grinder with tool rest
• 6-to-8-inch-long section of angle iron
• Pail of water

Instructions

1. Pull on the black rubber boot that covers the tip of the spark plug and disconnect the spark plug wire from the spark plug.

2. Turn the mower on its side. Place a ratchet and socket over the bolt in the center of the rotary blade. Hold the blade with one hand, and rotate the ratchet counter-clockwise to loosen and remove the bolt. Then lift the blade out of the mower deck.

3. Place the mower blade flat onto the tool rest of your bench grinder with the curled portion of the blade oriented upwards. Adjust the angle of the tool rest so that the cutting edge of the blade is flat against the grinding wheel, and tighten the wing nut on the tool rest to lock it in position.

4. Turn on the bench grinder, and grind the cutting edge of the blade until the entire face of the cutting edge is flat and even, with no nicks.

5. Turn the blade over, and repeat the previous step with the opposite cutting edge.

6. Place a piece of angle iron flat on a work table so that the V of the angle iron is pointing upwards. Position the rotary lawn mower blade onto the angle iron so that the hole is perfectly centered over the angle iron. The blade should be evenly balanced on the angle iron. If it leans to one side, re-grind that side on the bench grinder, then test the balance again. Repeat until the blade is perfectly balanced.

7. Replace the blade into the mower deck, and secure it by tightening the bolt with a socket. Be sure to position the blade so that the curved portion points upward toward the top of the mower deck.

8. Set the mower down onto all four wheels, and re-connect the spark plug wire to the spark plug.

Tips & Warnings

• When sharpening with a bench grinder, wear safety glasses to protect your eyes from flying sparks.

References

• Grounds Maintenance: How to Sharpen a Lawn Mower Blade
• Bob Vila: Sharpening a Lawn Mower Blade