How to Sharpen Your Lawn Mower Blades

Reel mower blades should be sharpened by a professional.

Lawn mowers with dull blades consume more fuel and cut grass with a tearing motion, rather than a clean slice. This stresses lawns and gives them a ragged, unkempt appearance. If grass blades have rough, browned edges after each mowing, the lawnmower blade probably needs sharpening. For best performance, sharpen lawn mower blades at least once each growing season. Although most hardware stores and lawn and garden centers offer blade sharpening services, easily maintain most lawn mower blades at home with a few simple tools.

Things You'll Need

• Gloves
• 2-by-4 block of wood
• Wrench
• Ratchet and spark plug socket
• Coarse tooth file
• Bench grinder, drill or Dremel tool (optional)

Instructions

1. Remove the gasoline from the lawn mower's fuel tank, or run the engine until the tank is empty.

2. Remove the spark plug with a ratchet and a spark plug socket of the proper size. This ensures the motor won't accidentally start if the blade rotates as you remove it.

3. Turn the mower onto its side, taking care to ensure the side with the air filter faces up. This prevents oil from leaking out onto the filter medium.

4. Wedge a 2-by-4 block of wood between the blade and the deck of the mower to immobilize the blade. Always wear gloves heavy enough to protect the hands when working around lawn mower blades.

5. Remove the bolts securing the blade to its shaft. If the bolts are frozen in place, apply penetrating oil or use a rubber mallet to loosen, taking care to keep hands and arms out of the path of the blade. Set the bolts and any washers aside in a safe place.

6. Remove the blade and secure the blade in a bench-vise, if available. Secure the blade to prevent wobbling, and make several passes on the cutting edge of each side using a coarse toothed file. Push the file toward the sharp edge of the blade, lifting up after each stroke. The file removes material as it pushes down, so avoid using a sawing or back and forth motion. Also use a bench grinder, Dremel tool or electric drill with the proper attachment, but files are more forgiving and user-friendly. Power tools generate heat and make it easy to remove too much material unintentionally.

7. Follow the angle of the originally sharpened blade, and only use the file on one side of the blade. The flat side of the lawn mower blade should not be sharpened. Sharpen the blades using an equal number of strokes, to avoid unbalancing the blade. Test the blade for balance by suspending it from a peg in the wall, or a screwdriver. If it leans to one side, remove material with a few more strokes of the file until the blade balances evenly.

8. Reattach the lawn mower blade, taking care to ensure the curved ends of the blade point up toward the deck of the mower.

Tips & Warnings

• Sharpen lawn mower blades more frequently in areas with rocky soils.

• Ensure the fuel tank is empty of gasoline before removing a lawn mower blade.

References

• University of Missouri; Plant Protection Programs; Sharpen Grass-Cutting Skills, Tools for Efficient Mowing Season; Bill Casady; 2007
• Kansas State University Extension; Sharpening Mower Blades Can Be DIY Job; Kathleen Ward; 2010
• Mother Earth News; A Midsummer's Sharpening: How to Sharpen Your Lawn Mower Blade; Troy Griepentrog; 2008
• Consumer Reports; Home & Garden; Weekend Project: Sharpen Your Mower Blade; Daniel DiClerico; 2009