How to Sharpen a Power Mower Blade

A dull mower blade doesn't cut grass blades--it tears them, leaving the grass vulnerable to disease or damage from the sun. How often the mower blade needs sharpening depends on the size of your lawn and how often you mow, but plan on doing the job at least every four to six weeks.

Difficulty: Moderate

Instructions

Things You'll Need:

• Bench Vise
• Flat Medium File
• Adjustable Wrench
• Screwdriver
• Block Of Wood
• Scraper Or Putty Knife
• Dowel Or Blade Balancer

1. Drain the gas and disconnect the spark plug wire in your power mower so the motor doesn't turn over while you're working.

2. Tilt the mower on its side, and wedge a block of wood between the blade and the mower deck to keep the blade from turning. You can also buy a device called a Blade Buster that locks the blade in place while you work on the mower.

3. Use a scraper or putty knife to clean any built-up debris from the underside of the mower deck.

4. Using an adjustable wrench, remove the bolt from the center of the blade.

5. Pull off the blade and clamp it in a bench vise.

6. Check the blade edges for small nicks, and remove them using a flat medium file.

7. Sharpen the blade by moving the file toward the cutting edge with smooth, even strokes. Follow the original bevel of the blade as closely as you can.

8. Make the same number of strokes on each edge. If you take more metal off one side than the other, the blade will be out of balance. An out-of-balance blade cuts unevenly; it also makes the mower vibrate, which can cause serious damage to the engine.

9. Test the balance by resting the blade on a dowel or the handle of a screwdriver. If one side points up, sharpen the other until the blade lies flat. (Or use a blade balancer, available at garden centers and hardware stores.)

Tips & Warnings

• Rather than fuss with a blade that's badly nicked or very dull, it's better to have it professionally sharpened-- or simply to replace it.
• Never touch the blades of any power mower until the spark plug is completely disconnected. Just a few drops of gas in the tank could be enough to make the mower's engine kick over when you move the blade.

[TheDon]

on 7/9/2008 Thank you for sharing

[ksat]

on 6/4/2007 When reattaching newly sharpened blade, be sure to use a wrench that will allow you to rotate it outside the bottom of the mower deck. This will prevent any potential injury in case the wrench slips off while tightening the bolts. If you need to, use an extension of some sort - a metal pipe is always useful in this case.

(I didn't do this recently and managed to severely cut by thumb and index finger on the sharpened blade.)

on 8/8/2006 The bolt likely loosens in the standard, counter-clockwise direction.
This may not be good for the shaft, but to loosen a really stuck bolt, you can try this: use a rag to hold a closed end wrench onto the bolt tightly, then hit the other end of the wrench with a hammer to start it.

on 3/31/2006 Use the "C" clamp to hold the block of wood in place. The wood keeps the blade from rotating while removing the retaining nut.

on 11/22/2005 Use a "C" clamp instead of a block, the block can slip possibly causing a serious hand injury.