How to Balance Lawn Mower Blades

Cutting blades on frequently used lawnmowers require sharpening annually. A critical requirement often overlooked is checking the balance of the blade after sharpening. Lawnmower blades are two-sided, and often damage is limited to one side only. The damaged side will require heavy filing while the opposite, undamaged blade will require only minimum filing. The disproportionate quantity of metal removed on opposite ends of the lawnmower blade will result in an unbalanced blade that will cause excessive vibration and rough engine performance, either of which can result in engine damage. To prevent this possibility, blade balancing must always follow blade sharpening.

Things You'll Need

• Flat two-sided metal file
• Screwdriver
• Bench vice

Instructions

1. Remove the lawnmower blade, and inspect both sides of the blade for nicks or damage. Check the balance of the blade by inserting the shaft of a screwdriver into the hole in the center of the blade. Hold the screwdriver by its handle in a horizontal position, and allow the blade to teeter on the shaft. If one side of the blade dips lower than horizontal, this side is heavier than the opposite side and the blade is out of balance.

2. Re-balance the blade. Lock the blade in a bench vice with the sharp/cutting edge of the blade facing up as you file the heavy side with the coarse surface of a metal file. When filing the cutting blade, take care to align the file face with the angle on the cutting blade. Begin filing on the outside edge of the blade, making 6 full strokes of the file before repositioning the file a distance half its width in the direction not yet filed. This ensures that each file movement will overlap the previously filed section of the blade. Continue this overlapping filing until the entire surface is filed.

3. Remove the blade from the vice, and recheck the balance by inserting the screwdriver in the hole in the blade. If the blade continues to indicate one heavy side, repeat the filing technique in step 2.

Tips & Warnings

• If the blade is heavily damaged by nicks or other voids in the metal, use the coarse edge of the flat file to remove any burrs or nicks. If the blade is only slightly out of balance, use the fine edge of the flat file.

• Wear gloves during filing to avoid cuts as lawnmower blades can be very sharp

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References

• Blade Sharpening Technique