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How to Sharpen a Lawnmower Blade

When it comes to mowing your lawn, few factors are as essential to the quality of the cut than the sharpness of the blade. While a sharp lawnmower blade cleanly severs the individual grass leaf blades and produces a professional-looking finish, a dull blade rips the grass instead of cutting it cleanly, leaving it weaker and more prone to disease. While it's a simple matter to routinely run a file over a lawnmower blade that's in good condition to keep it sharp throughout the mowing season, it takes a bit more work to sharpen a dull mower blade that has been neglected.

How to Sharpen Mower Blades

If you would like to bring your mower's dinged-up blade back to like-new sharpness, and you have access to a bench grinder, follow these simple steps to renew its cutting ability.

  1. To prevent the lawnmower from accidentally starting, disconnect the spark plug wire; then flip the lawnmower on its side and remove the blade. Use a wooden block and a C-clamp to keep the blade from turning while you loosen the blade's mounting nut.
  2. Run the blade back and forth perpendicular to the grinding wheel to remove any nicks. Don't try to create a sharp edge in this step—simply grind out the damage to create a dull, straight edge.
  3. Use a support plate to rest the blade against the wheel at the angle of the blade's existing bevel, and grind the length of the blade until there's a sharp edge. While a blade angle of 40 to 45 degrees is most common, variations are possible, so check with the blade's manufacturer to obtain the exact degree measurement. Grind both cutting edges of the blade equally, so that an equal amount of metal is removed from both ends.

Balancing the Blade

An out-of-balance lawnmower blade will cause severe vibration when it's spinning and can actually damage the lawnmower's engine. To check if your lawnmower blade is properly balanced, purchase a plastic blade balancer (these are not costly). Set the balancer on a flat surface and rest the center of the mower blade on the balancer. If the blade remains horizontal, then it's balanced. If, however, the blade dips to one side, use the grinder to remove some steel from that end (but not from the cutting edge itself).

Once the blade is balanced, re-install it on the lawnmower and reconnect the spark plug wire, and your lawnmower will be ready to tame your turf.