Project Guide

How to Sharpen Lawn Mower Blades

How to Tell If You Need to Sharpen Your Mower Blade
Man checking lawn mower blade.

Time and use can make lawn mower blades dull which can result in torn grass, an uneven cut and lawn weakness and disease. Once you notice brown, frayed edges of grass, it’s time to use a lawn mower blade sharpener. Follow the steps below to learn how to sharpen lawn mower blades with ease. 

Remove the Spark Plug Wire

Be sure to disconnect the spark plug and the power source. 

This must be done to ensure that the mower does not accidentally start while you’re working on it as that will cause serious injury. 

Tip: For safety, wear gloves and protective eye gear. 

Remove and Clean the Blade
Man working on lawn mower

Tip: To avoid installing the lawn mower blade upside down, mark the bottom area of the blade with spray paint so you can quickly identify the underside. 

  • Turn the mower on its side to access the blade. Use caution when turning the mower over and be sure that the air filter and the carburetor are facing up. 
  • Using a wrenchMowers trap dirt, mulch and lawn clippings which can make sharpening more tedious. 
  • Using a dry rag, take a few minutes to clean the blade before sharpening it. 
Sharpen the Blade

ip: Always wear gloves and long sleeves when working with grinders and blades.

Lawn mower blade sharpening can be done either by hand with files, chisels and punches or with a machine like a bench grinder. 

If you are sharpening by hand

  • Sharpen the edge of the lawn mower blade using a file or grindstone, keeping the blade at roughly a 45-degree angle.
  • Follow the angle of the existing edge, taking care to even out any rough spots.

If you are sharpening with a bench grinder

Tip: Bench grinders often send sparks and debris into the air, so it is important to wear protective eye gear. 

  • Sharpen the blade by moving it back and forth against the wheel of the grinder. 
  • Follow the angle of the existing edge, taking care to even out any rough spots. 

The ideal result you want is a blade that is about as sharp as a butter knife, not a steak knife. The blade doesn’t need to be extra sharp to get the job done. 

Check the Balance

Mowers run smoother when the blade is balanced. 

  • Check the balance by supporting the blade under its center with a rod or other narrow horizontal support and then spin it to check its balance.
Reinstall the Blade
  • Replace the blade, taking care to knock out any chunks of mud or grass that may have accumulated under the mower. 
  • Remember to look for the marking you made earlier in the process. This should make it easy to find the right positioning. 
  • Use your wrench to tighten the bolt. 
  • Reconnect your spark plug wire. 
Maintaining Your Mower Blade
A well-trimmed lawn

Now that you know how to sharpen lawn mower blades, you'll want to use your lawn mower blade sharpener once or twice during the mowing season to maintain a healthy lawn. However, if you tend to mow more often, you may want to sharpen it more often. 

If your blade has dents or cracks, replace it. Blades that are damaged won’t respond to lawn mower blade sharpening and will only cause more damage to your lawn.