How to Sharpen a Lawn Mower Blade

Follow this easy tutorial to keep your mower working at its best.
How to sharpen a lawn mower blade

How to sharpen a lawn mower blade

Photo by: Photo by Debbie Wolfe

Photo by Debbie Wolfe

If you mow your own grass, you need to know how to sharpen the blade on your mower. A sharp blade saves time and energy while mowing, ensures a clean cut, and even helps to minimize the spread of lawn fungus. This task will take about fifteen minutes per blade, and the only equipment required is a wrench, a 24” piece of 2x4 or 3” diameter pipe, a vice and a file. Keep these few items close at hand and you can make quick work of it.

How do you know if your blade needs to be sharpened?

Here are some signs that you should sharpen your mower blade:

  • The mower leaves a rough, ragged finish.
  • The blades of grass look torn rather than cut.
  • A day or so after mowing, the grass has brown tips.
  • It’s been at least a year since it was sharpened.

How often should you sharpen your mower blade?

If the mower is used regularly, plan on sharpening at least once a year. A yearly sharpening should go hand-in-hand with an oil, filter and spark plug change, to keep your baby purring like a kitten. If it is used heavily or there are a lot of weeds, sticks, or other debris in the grass, up to several times per summer may be necessary. If multiple sharpenings per season are required, consider buying a second blade (or set of blades) to have on hand for a quick change out that can save time on mowing day and allow sharpening to be done when it’s most convenient.

Mower blades should last a very long time, possibly the life of the mower. However, an unsafe or worn out blade should be discarded and replaced with a new blade matching manufacturer specifications for your mower. Discard a blade when it is bent, cracked, worn thin on the back edge (opposite the cutting edge), deeply rusted, or otherwise structurally compromised.

Sharpening a lawn mower blade

  1. Disconnect the spark plug or remove the battery to prevent an unintentional start.
  2. Tip the mower up on its side.
  3. The side with the carburetor and air filter should be on top.
  4. Block the blade with the piece of 2x4 or place a piece of 3” pipe through the side discharge and over the blade to hold it in place.
  5. Use the wrench to remove the bolt which holds the blade in place.
  6. Set the bolt and washer aside where they will not be lost.
  7. Clamp the blade in the vice, in “cutting position” with the first end to be sharpened extending 3 or 4 inches beyond the jaws of the vice.
  8. Following the original angle of the cutting edge (approximately 30 degrees), and with long steady strokes, use the file to smooth the rough cutting edge back to a flat sharp surface.
  9. For quick grinding action, a double-cut file will remove a lot of material fast.
  10. For honing and creating a final edge use a single-cut file.
  11. Double sided files are available with one side single-cut and the other side double-cut.
  12. When the first end is complete, re-position the blade and sharpen the other cutting edge.
  13. Once both sides are sharp, check the balance of the blade by hanging it on a nail through the bolt hole.
  14. If it hangs horizontally, it’s ready to re-install.
  15. If one end hangs lower than the other, file a bit more off that end’s edge until the blade balances on the nail. This will ensure that the mower runs smoothly.
  16. Re-install the sharpened, balanced blade.
  17. Remember to use the 2x4 or pipe to stabilize the blade as you tighten the bolt.
  18. Reconnect the spark plug wire. You’re ready to mow!
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