How to sharpen lawn mower blades

The best way to sharpen lawn mower blades

To have the healthiest lawn, you’ll want to cut the grass roughly once each week as removing only the top third of the grass blade promotes growth. To effectively achieve this without damaging your grass, you’ll need to sharpen your lawn blade consistently.

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Why do I need to sharpen my lawn mower blade?

When you mow your lawn with a dull lawn mower blade, the grass doesn’t cut. It tears. The jagged edge of a torn grass blade allows diseases to enter the grass blade. Not only will this make your lawn unhealthy, but instead of lush green, the tips of the torn grass will give your yard a dull, brownish cast.

When to sharpen your lawn mower blade

There are two quick and easy ways to tell when your lawn mower blade needs to be sharpened: look at the grass or look at the blade.

Look at the grass

After mowing your lawn, inspect the grass. If the grass has a clean cut across the top, you’re fine. However, if the cut mark is jagged and uneven, it’s time to sharpen your blade. Also, you can scan the lawn after mowing to gauge if all the grass blades are at the same height and check to see if the property has a brown cast.

Look at the blade

The second way to tell if your lawn mower blade needs to be sharpened is to inspect the blade. If there are any nicks, dents or the cutting edge is visibly dull, it’s time to sharpen the blade. If the blade looks bent, however, it is time to get a new blade.

How often do I need to sharpen my lawn mower blade?

As a rule of thumb, always sharpen your lawn mower blade before the first cut of the season. After that, use the methods mentioned above to gauge when to sharpen again. Depending on the size of your lawn, you will likely need to sharpen your blade two or three times per season.

Additionally, if you ever hit something solid with your lawn mower, like a rock or a root, you should immediately stop mowing the lawn and inspect the blade to ensure it is not bent. Even if the blade is in good condition, chances are it will still need to be sharpened before your next mowing.

A step-by-step guide to sharpening lawn mower blades

Before beginning, remove the spark plug wire from the spark plug to make it impossible for the lawn mower to start up unexpectedly.
Tip the lawn mower back, so the spark plug is facing up. If you tip the mower to the side, you’ll have a greater chance of the gas or oil leaking. Alternatively, you can drain the fluids from your lawn mower before tipping it back.
Insert a large block of wood into the mower to keep the blade from spinning while loosening the nuts that hold it in place. If this is your strategy, make sure the wood stays perpendicular to the blade. Otherwise, you might accidentally bend the blade. Alternatively, you could put on a cut-resistant work glove so you can safely hold the blade while loosening.
Using the proper size wrench, remove the two nuts that hold the blade to the lawn mower.
Clean the blade.
Put the lawn mower blade in a vice and clamp it in securely so the edge you want to sharpen is facing up. Using a metal file, follow the angle of the blade and make long strokes in a downward direction until the blade is sharp.
If you prefer, you can use a lawn mower blade sharpener that attaches to a handheld drill to sharpen the lawn mower blade. Before using, put on a pair of safety glasses. Then, insert the lawn mower blade between the plastic guard and sharpening stone and simply run the blade sharpener along the blade edge.
Alternatively, you can use an angle grinder or a bench grinder to sharpen your lawn mower blade. You must wear eye protection here as well.
Flip the blade over so you can sharpen the other side.
You must remove the same amount of material on each side, so the blade stays balanced. To check this, place the lawn mower blade on a lawn mower blade balancer. If one side tilts down, that side will need to have more material removed.
Clean off all the grass from the bottom of the lawn mower before mounting the lawn mower blade and tightening the nuts.