How to Sharpen Lawn Mower Blades at Home

The secret to a great-looking lawn is sharp mower blades. Unless you have a sharp blade, the grass gets shredded – not cut – and turns brown. 

Being able to keep your blades sharp ensures your grass stays healthy. Not only that, your mower will last longer as well.

This guide explains everything about sharpening lawn mower blades.

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When to Sharpen Your Blade

All mower blades get dull over time. Always check the blades after use. If they are looking a little worn, it’s time for a sharpen.

Generally, you need to sharpen the blades twice per mowing season. Or, if you’re a heavy user, after every 25 hours of service. You should re-sharpen the blades, too, if you accidentally hit rocks.

The state of the lawn is also a good indicator.

Tell-tale signs it’s time to sharpen your blades include:

  • Damage to the blades
  • Uneven grass cutting
  • The grass looks torn rather than cut
  • Brown grass

Blade Removal and Cleaning

Image of the mower blades on underside of a lawnmower laid on its side.

First, disconnect the mower’s power source and remove the spark plug lead.

Next, follow these steps:

  • Put on your protective gloves and eyewear
  • Drain the fuel tank
  • Flip the mower carefully onto its side. Keep the carb and air filter upward
  • Mark the blade permanently so you know which way to refit it.

Remove the nut fastening the mower blade with a socket wrench or ratchet. You may need to brace the blade with wood.

Use a dry cloth to clean the blade before you sharpen it. Remove stubborn deposits with a spray of penetrating oil and a stiff brush.

Sharpening your mower blade

Place the blade in a vise or worktable with the cutting edge facing upward. Examine the blade for damage. If it is cracked or dented, you will need a replacement.

Nicks or bends can be buffed out.

Don’t over-sharpen. The blade need be no sharper than a butter-knife. A razor-like sharpness dulls quickly, and the blade will need replacing sooner.

Pro tip: Always wear protective gear, including ear defenders, if you’re using a machine.

Sharpening by hand

Don protective eyewear and gloves. Sharpen the blade with a ten-inch file or a grindstone. The file should be kept at 45-degrees.

Work in one direction only. You are using the correct amount of pressure if you feel the file’s teeth on the blade.

Follow the blade’s edge and work out rough spots. When finished, release the blade and flip it over to sharpen the other face.

Sharpening with a drill blade sharpener

Put on your safety gear to protect your hands, eyes, and hearing.

Fix the blade into a vise. Fit the blade sharpener to your drill. Sharpeners are round, bevel-edged grindstones, with a guide piece and quarter-inch shank.

With the drill powered up, place the grindstone on the mower blade. The guide should rest against the back of the blade. The cutting blade edge fits into the bevel and gives the correct sharpening attack angle.

Apply medium pressure as you move along the edge of the blade. Check after four passes to ensure the blade is free of any roughness. Make a couple more passes if not satisfied.

Swap the blade over and sharpen the other face.

Sharpening with an angle grinder

Sharpening mower blades with an angle grinder

Make sure to wear you safety gear!

Place the blade securely in a vise and fit a flat disk to your angle grinder.

Slowly move the grinder along the cutting edge of the blade. Take out rough patches and then turn the blade over and repeat.

You can check the sharpness by running a piece of paper or a blade of grass over the blade. It should cut effortlessly.

Checking the lawn mower blade balance

The process of sharpening inevitably affects the balance of the blade.

If a blade has become unbalanced, it’s essential to remedy this as an unbalanced blade can cause severe damage to your mower.

To balance the blade:

  • Support the blade at its center by placing it on a wall nail or a rod clamped to a worktable.
  • Hold the blade horizontally, then let go. If it is unbalanced, it won’t remain level.
  • Take a note of which side dipped, take off a little metal from there and retest.

However, a cone-shaped blade balancer is more precise.

Refitting the lawn mower blades

When sharpened and balanced, before refitting the blade, take the opportunity to clean around the mower’s blade housing and underside.

When cleaned, refit the blade. The mark you made earlier will show which side of the blade faces you.

Place the blade onto its bolt and tighten the nut. Ensure the blade is nice and secure.

Refit the spark plug lead and the power source. Top up the fuel tank and start-up your mower outdoors.

Maintaining the mower blade

Sharpen your mower blade once or twice a season. More often if you’re mowing more frequently.

Sharpening the blade as required will keep your lawn and your mower in excellent shape.

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