How To Sharpen Mower Blades

a mower getting sharpened on a grinding wheel

Step 1: How to tell if you need to sharpen your mower blade (we practice sharpening blades twice per week).

Clean cuts with a sharp mower promote good lawn health. A properly mowed lawn helps prevent lawn disease from getting a foothold. The cut grass also returns nutrients to your lawn, so it grows even stronger.

Over time, lawn mower blades get dulled by usage. Regularly inspect the mower blades after mowing. When they’re looking worn, you’ll need to remove the blade from the lawn mower and hone the edges.

In general, sharpen twice per week or after 20 hours of use to keep your blades in good shape. Also, sharpen the blades after hitting rocks. Stone can easily dent or nick the blades.

The lawn itself can also hint when you need to sharpen your mower blades. If it’s not recovering well after mowing, that’s a clue.

Look for these signs that you may need to sharpen the mower blades:

  • Dents or nicks in the mower blades
  • Uneven grass height after cutting
  • Grass blades look torn instead of sliced
  • Brown, frayed grass edges

Step 2: Remove and Clean the Blades

Once you’ve determined that you need to sharpen the blade, it’s time to remove the blade from the lawn mower.

Before you begin, disconnect the spark plug wire from a gas mower. This protects you from any surprise hiccups of power. Follow these steps to remove the lawn mower blade.

  • Put on work gloves and protective eyewear for safety.
  • Carefully drive up on the mower ramps.
  • Place two tire chocks behind the rear wheels and engage the park break.
  • Mark the bottom of the blade with a permanent marker, grease pencil or spray paint. That way, you can install the sharpened blade right-side up later.
  • Find the nut that holds the mower blade to the drive shaft. Use an impact drill on the nut until the mower blade releases.
  • If it’s tough to grip the nut, get more leverage. Brace the blade with a piece of scrap wood and clamp the blade still. You should be able to remove the nut now.
  • If the nut and threaded shaft are rusted or stuck together, apply penetrating oil and allow to sit for a few hours.
  • Clean the blade with a dry rag or microfiber cloth before sharpening it.
  • Sometimes the blade is unusually dirty or caked with grass clippings. When that’s the case, spray it with some penetrating oil. Let it sit as directed, then scrub the debris away with a stiff brush.

Step 3: How to Sharpen the Lawn Mower Blade

Next, gather the tools to sharpen lawn mower blades. Mower blades have a 3- to 4-inch cutting edge on opposite sides of the blade. Check to see if the blade is dull or damaged.

  • Clamp the mower blade into a vise or onto a worktable with the first cutting edge facing up.
  • Examine the blade. Decide if it is better to sharpen it or replace it.
  • If your blade has cracks, is missing large pieces, or is severely bent, replace it. You shouldn’t sharpen a heavily damaged lawn mower blade.
  • If your blade is just nicked, chipped, or dull, try sharpening it.

Only sharpen the blade so it’s as sharp as a butter knife. The edge shouldn’t cut your finger. A razor-sharp blade dulls more quickly. You’d have to replace the blade more often after constant resharpening. A gently sharpened and shiny edge is the goal.

Safety Tip: Always wear gloves, long sleeves and eye protection when working with grinders and blades. Wear ear protection if you’re using a machine method of sharpening.

Sharpen a Lawn Mower Blade with an Angle Grinder:

  • Put on your safety gear. This includes work gloves as well as eye and ear protection.
  • Use a vise to clamp the mower blade still.
  • A flap disc is a good choice for the angle grinder.
  • Align the blade of the grinder with the cutting edge of the mower blade.
  • Move the grinder slowly back and forth against the edge of the mower blade.
  • Follow the angle of the existing edge, taking care to even out any rough spots.
  • Finish one edge of the mower blade.
  • Repeat the process by turning it over and grinding the other edge.

When the blade looks complete, check the sharpness. Grab a blade of grass or a piece of paper and pull it over the blade. It should cut easily.

Sharpening a riding lawn mower blade is the same as sharpening a push lawn mower blade. Use the informative steps above to stay safe and keep your lawn mower performing optimally.

Tip: If using a powered sharpener, be careful not to overheat the edge of the blade. If it’s too hot to touch, it’s too hot. The blade can be cooled by dunking it in a bucket of water.

man changing out the blades of a push mower

Step 4: Check The Blade Balance

Mowers run smoothest when the blade is balanced. However, sharpening sometimes removes more metal from one edge than another. This makes the blade unbalanced.

It’s important to fix a blade that was imbalanced during sharpening. If it wobbles now, it will wobble on your mower too. An unbalanced blade may damage your mower. The vibrations alone are annoying, but the bearings or blade shaft might actually get destroyed.

Follow these steps to check the balance on your sharpened lawn mower blade:

  • Support the blade under its center, like a scale. A screwdriver is an easy tool to use. Insert the screwdriver tip through the hole in the blade. The blade should balance on the tip or drop to balance on the handle.
  • Hold the blade horizontal, then let go. It should remain level.
  • If the blade drops in either direction, it means that the blade is unbalanced.
  • The side that dipped down is heavier. Take a few strokes off that end to remove some metal, then retest.

Step 5: Reinstall the Blade

After sharpening the lawn mower blade, reattach it. It’s also an excellent opportunity to clean the bowl around the blade.

  • Before reinstalling the blade, wipe the area under the mower clean. Dig out any mud and grass clippings that have caked under there too. A paint scraper or putty knife works well for this.
  • Check your blade for the grease pencil or paint mark you made earlier. That’s the bottom of the blade.
  • Insert the blade back onto the bolt. The marked side should face you as it did before.
  • Use your impact drill to tighten the nut. Make sure the mower blade is secure. It needs to be tight for your mower to start smoothly.
  • Reconnect your spark plug wire and your power source.
  • Check to see that your mower starts smoothly.