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Sharpening Your Mower Blade

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BLACK+DECKER B+D Contributor 193 Projects

The blade is an incredibly important part of the mower. If the blade is in poor condition, it can affect your entire lawn. And the negative effects aren’t just related to appearance. A ragged top cut on a leaf of grass opens the grass plant up to disease. That’s why keeping your lawnmower blade sharp is the first line of defense against lawn diseases.

Sharpening your blade is a simple task that should be done at least once every season (and it certainly doesn’t hurt to do it more than once). Before you inspect for nicks or other obvious damage, clean the blade with a wire brush. Serious dents, cracks, or deep nicks in the blade mean it’s probably time for a replacement blade. If you can’t remove the nick fairly easily during the sharpening process, you’ll need to replace the blade.

How to Sharpen a Mower Blade

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    Remove the spark plug or battery from the mower, or otherwise disable it so that it cannot accidentally start. Tip the mower on its side, so that the entire underdeck area is accessible. 

    Tip: If your fuel tank contains gasoline, remove the cap, cover the opening with foil or plastic wrap, and then replace the cap. This prevents gas from dripping out of the vent hole in the cap.

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    Wedge a wood scrap piece between the blade and the mower deck to stabilize the blade so it doesn’t spin while you remove the bolt holding it in place. You can also purchase a special device for this purpose from yard and garden centers

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    Use a closed-end wrench to loosen the bolt that secures the blade to the mower motor. If the bolt is stuck, try spraying it with penetrating lubricant and letting it soak in for a few minutes before retrying.

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    Inspect the entire blade for damage, and then file along the cutting edge, using smooth, even strokes at an angle that matches the existing bevel. Use the same number of strokes on each edge.

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    Check the blade’s balance by hanging it on a nail that has been driven into the wall. The blade should hang level. If the blade is not balanced, file metal off the heavier end until it is.

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    Balancing a mower blade is an important last step before you reinstall the blade on the mower. If you don’t feel comfortable hanging the blade on a nail and judging it on the wall, you can lock a screwdriver horizontally in the vise and slide the blade onto the shaft. You can also buy a blade-balancing cone at your hardware store or lawnmower retailer. Simply sit these on a flat, level surface, slide the blade on top, and check the balance.

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    Reattach the blade to the mower’s motor following the manufacturer’s instructions and cut a small strip of grass as a test. Inspect the tops of the cuttings to make sure they have been sliced cleanly, indicating that the blade is sharp.

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