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How to Balance a Rotary Lawn Mower Blade After Sharpening

If you sharpen your own rotary lawn mower blades, it is essential that you sharpen them evenly. Unbalanced sharpening can make a blade heavier on one side than on the other, which can lead to heavy vibration, the loosening of internal structural bolts, and accelerated engine wear. Fortunately, it's easy to test the balance of a blade and make adjustments prior to reinstalling it, so you should never have to deal with this kind of damage if you take heed of the steps outlined below.

Drive a large nail into a wall joist in a garage or shed using a hammer. Balance the lawn mower blade on the end of this nail by putting the hole in the blade's center over the nail head.

Turn the blade about a 1/4 turn to the right, and let go of it. If it stays in place, that's a good sign. If it turns right back to where it started, that's a bad sign. Try turning it a half turn to the right. Again, if it stays put, the blade is well balanced. If it rotates back to where it started again, the section of the blade that keeps returning to the bottom is too heavy.

Remove the blade from the nail, keeping track of the part of the blade that has been determined to be too heavy. Clamp the blade to a work bench or sturdy surface using vice clamps.

Use a smooth file to file down the edges of the heavy side of the blade. Be careful to maintain the original angle of the blade's edge as you file.

Take the blade off of the clamp, carefully brush it clean with your hand and place it back on the nail. Turn the balanced blade several times to see if the same section keeps settling at the bottom.

Continue alternating between filing and balancing on the nail until the blade stays put no matter which way you turn it on the nail. Reinstall the blade on your lawn mower whenever it appears to be well balanced.


Some hardware stores sell plastic fulcrums that can be used to measure rotary blade balance with greater accuracy. If you make a habit of sharpening your own blades, this may be a worthwhile investment.


Sharpening blades is a task that takes some skill and great concentration. If you don't watch what you're doing, you can easily cut yourself, so use extreme caution.

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