How to Sharpen Your Lawn Mower Blade

Preventative maintenance improves a gas-powered lawn mower’s overall lifespan and performance with the goal of saving you time and money. It also has a huge effect on how well your grass performs. In a previous Sod University blog, Sod University discussed the importance of Winterizing Your Lawn Mower. However, this particular article expands on step 3 of the previous blog post: removing and sharpening the lawn mower blade. Read below to learn how to sharpen your lawn mower blade and find out why sharpening it helps your lawn mower perform better during the mowing season.

Why You Should Sharpen Your Lawn Mower Blade

It turns out that after years of usage, your lawn mower blade might be dull. Maybe it’s functioning more to “whack” your grass blades in place of neatly cutting them at the appropriate height. If your mower blades haven’t been sharpened in a long time, you’re probably spending a lot more time than needed mowing the lawn because your mower’s blades aren’t cutting the grass as efficiently. When a dull blade is cutting your grass, it’s actually ripping and pulling the grass blades, which leaves tears that weaken the plant and leaves the grass more vulnerable to disease.

Photo Credit: www.hutsoninc.com

Equipment You’ll Need:

• Spark Plug Socket,
• Spray Paint (Optional),
• WD-40 (Optional),
• Gloves,
• Wire Brush,
• 10-inch Mill Bastard Hand File OR an OGS Lawn Mower Blade Sharpener,
• Vise (For the Hand File Option), and
• Balancing Tool OR use a nail in the wall (refer to step five).

1. Safety First: Remove the Spark Plug

Although this task may seem difficult because you are messing with equipment, it is actually a simple task. The first thing to always remember is to be safe in removing a blade. As stated in our previous lawn mower blog, removing the spark plug is one of the best moves you can make so the mower doesn’t accidentally kick-start. Use a spark plug socket to remove the spark plug as pictured below. Be sure to clean the debris around the spark plug so that it doesn’t fall into the hole once the spark plug is removed.

2. Removing the Lawn Mower Blade

The next step is removing the lawn mower blade. But first, mark your blade with spray paint before you remove it so you remember which way to reinstall the blade when you have finished sharpening it. You don’t want to install the blade backwards after sharpening it because it won’t cut. Next, you will want to loosen the single nut or bolt holding the blade on so you can remove the lawn mower blade. These bolts tend to be very tight so that the lawn mower blade stays in place securely. You may need to use a breaker-bar or long handle wrench with a socket to match the bolt. Fortunately, this simultaneously keeps your knuckles at a greater distance from the blades as you bear down on the nut or bolt. If this still isn’t working, apply penetrating oil like WD-40 and wait 10 minutes for it to soak in.

3. Cleaning the Lawn Mower Blade

Once you have removed the blade, you will want to take a wire brush to it and clean off all of the debris that has accumulated over time. Scrubbing it to get the debris off is not going to hurt the blade. Use gloves to keep from potentially cutting yourself or getting your hands too dirty.

4. Sharpening the Lawn Mower Blade

Now that the blade is removed, you can begin sharpening it. We suggest using a 10-inch long mill bastard hand file such as the one pictured below. We also really like the OGS Lawn Mower Blade Sharpener that attaches to the end of a drill-bit so that you don’t have to put in as much manual labor sharpening with a file. A grinder can also work for this same project, but they’re a little more difficult to control and are usually used by professionals. Lawn mower blades are also made of a fairly soft steel, so you don’t want to overheat and ruin the blade with a grinder either.

Hand File

When sharpening with a file, you will want to clamp the blade in a vise and sharpen the cutting edge with the file. Sharpen from the top side of the cutting edge as it will give you a longer-lasting edge on the blade. When you push in the single direction the blade was designed for, you’ll feel it bite into the steel. Press down harder if you don’t feel it. Lastly, don’t try to make your lawn mower blade too sharp—it’ll dull much more quickly.

Drill Attachment

If you choose to use an OGS Lawn Mower Blade Sharpener, the attachment easily connects to a drill. Use the backside of the attached tool to run it over the blade after turning it on. The backside is flat and at the perfect angle for the blade. See the video below for a visual example.

5. Balancing the Blade

For this step, you can either use a handy nail that has been nailed into the wall or a balancing tool to balance the weight of the blade so that you don’t take off more weight from one side of the blade and not the other. It is important to keep the sides of the blade balanced so it doesn’t wobble and move on your bearings. You will need to take off more metal on one side of the blade if the blade does not balance properly. If you use a nail in the wall, set the blade on top of it like an airplane propeller and see it balance. It is important to note that you must be very careful with this so it doesn’t fall and hurt anyone. Wear gloves to protect your hands and closed toe boots for your feet. 

6. Reinstallation

Reinstall the blade onto your lawn mower and hand-tighten the bolt. Use the mark you made in step four to ensure you install the blade in the right direction. It is good to know that it is difficult to over-tighten the bolt. Under-tightening the bolt promotes a loose blade that can throw off the engine timing and cause problems when starting the mower.

For more information on sharpening a lawn mower blade yourself, we recommend taking a look at Family Handyman’s blog: How to Sharpen Lawn Mower Blades. Learn more about other things you can do to perform preventative maintenance on your lawn mower here: Winterizing Your Lawn Mower. For a full lawn mowing guide with mowing heights for specific grass types, check out our Lawn Mowing Guide blog. Lastly, be sure to look at our reel mower vs. rotary mower blog to find out which type of mower fits your needs if you are looking to get a new lawn mower anytime soon.