How to Sharpen Lawn Mower Blades

Lawn mower blade sharpening

The key to a well-manicured, healthy lawn is a clean cut. Your lawn mower’s blades will become dull with use, and they’ll tear your grass instead of cutting it cleanly. While you can get them sharpened, you’ll save more money if you learn how to sharpen lawn mower blades yourself. Don’t know where to start? Don’t worry; we’ll teach you!

Does My Mower Blade Need Sharpening?

The best way to know if your mower blade needs sharpening is by looking at your grass after a mow. Since dull blades tear turf instead of cleanly cutting it, your lawn will look a little different — in a bad way. Seeing these signs mean your mower blades are in need of sharpening:

  • Torn, brown grass blade edges
  • Unevenly cut grass
  • Poor grass recovery after being mowed (which can lead to lawn disease)
  • Patches after mowing (from super dull blades that yank out grass)
Sharp Blade infographic
Infographic by Juan Rodriguez

Generally, you should sharpen your mower blades after 25 hours of use. 

You’ll also want to sharpen at the start of spring as part of your regular lawn mower maintenance before the first mow of the year.

Lastly, you’ll also need to sharpen your mower blade if you hit a rock or other object while mowing. Hitting rocks will nick your blade.

How to Sharpen Lawn Mower Blades DIY

close-up of lawn mower blade that is chipped
Photo Credit: JJ Gouin / Canva Pro / License

These instructions are for a walk-behind push mower. Sharpening the mower blades of a walk-behind mower and a riding mower will stay relatively the same. The only difference is how you remove and reinstall the blade.

Tools and Materials to Sharpen a Mower Blade

Before starting this project, you need the following tools and materials:

  • Protective gear
    • Work gloves
    • Safety goggles
    • Face mask
    • Long sleeves
    • Hearing protection (if sharpening with a machine)
  • Tape
  • Permanent marker or spray paint
  • Rag or cloth
  • A wood block
  • Ratchet and socket or a wrench
  • WD-40 or another brand of penetrating oil
  • Putty knife, wire brush, or paint scraper
  • Vise or clamp
  • Sharpening tool (pick one)
    • Metal file (at least 10 inches long)
    • Blade sharpener drill attachment
    • Bench or angle grinder
  • Blade balancer, screwdriver, or a nail

Step 1: Put On Protective Gear

Because you’ll be dealing with a blade, you should wear protective gear. Use a pair of thick work gloves, a face mask, long sleeves and safety goggles. Sharpening your mower blade shaves off metal in very small parts, which can get in your eyes or your nose.

We also recommend wearing some form of hearing protection if you plan to use machinery to do the job.

Step 2: Prepare the Lawn Mower

You want to make sure your mower can’t start up accidentally as you are removing and replacing the blade. Otherwise, you could severely injure yourself. Lawn mower blades can spin more than 3,000 rpm!

This process will be different based on your mower’s power source:

  • Gas-powered mowers: Disconnect the spark plug wire. Tape it to prevent any chance of it from coming into contact with the plug.
  • Electric mowers: Unplug the cord or remove the battery.

After disconnecting it from its power source, you should tilt the mower on its side. If you have a gas-powered lawn mower, make sure the air filter and carburetor are facing up. Otherwise, fuel may spill onto them and cause a belch of smoke upon restarting.

Pro Tip: If you want to be extra sure you won’t have a fuel spill, empty the gas tank. Sure, it’s more work, but it’s better safe than sorry.

You also can place the mower up on blocks to access the underside of the mower without tipping it over. You will need to do this if you are going to sharpen the blade of a riding lawn mower.

Step 3: Remove the Mower Blade

tightening a lawn mower blade
Photo Credit: KathrynHatashitaLee / Canva Pro / License

Now that you can access the blade, it’s time to remove it. First, keep the blade still. You can wedge a wooden block – a 2×4 works fine – between the blade and the deck. Try to keep it at a 90-degree angle so there’s no risk of your blade bending. You also can hold the blade as you’re removing it, but it’s much riskier.

Use a marker or spray paint to make a mark on the blade to make sure you know which side is the bottom side. You need to reinstall the blade the correct way after sharpening it. Some blades distinguish them with text, eliminating the need to mark them.

Pro Tip: Take a picture of the blades before you remove them so you have a reference to look at when you reinstall them.

To remove the blade, use a ratchet and socket or a wrench to detach the bolt, nut, or series of nuts fastening the blade to the mower. You can consult your mower’s manual to see if there are any quirks to detaching the blade. The guide also will likely tell you the proper size wrench or socket to remove the hardware holding the blade in place.

If the hardware is stuck on too tight, try soaking it with penetrating oil or using a long-handled wrench for more torque. If the hardware is rusted, soak it with penetrating oil.

Step 4: Clean the Mower Blade

Next, clean the blade. Wipe and/or rinse off grass, mud, and dirt, and soak the blade in penetrating oil if it’s especially dirty. Make sure the blade is dry before working on it. 

You also can take this time to clean the underside of the mower. Rinse and wipe away dirt, grass clippings, and rust. If the dirt is caked onto the mower, then you can use a paint scraper, a putty knife, or a wire brush to scrape it off.

Step 5: Inspect the Mower Blade

Before working on the blade, you should take a good look at it. Secure the mower blade with a vise or a clamp and inspect it. A few dents and a dull blade mean that you will need to sharpen it. It shouldn’t be more damaged than that. Strongly consider getting a replacement mower blade instead if your mower blade is:

  • Cracked
  • Missing large chunks
  • Bent

Don’t remove the blade from the vise or clamp. You want to keep the mower blade securely in place while sharpening it.

Step 6: Sharpen the Mower Blade

lawn mower blade sharpening
Photo Credit: isuaneye / Canva Pro / License

There are many ways to sharpen a mower blade:

Each method has its pros and cons. Let’s take a look at them. Before you start, your mower blade has to be held in place by a clamp or vise.

How to Sharpen a Mower Blade With a Metal File

You can sharpen a mower blade by hand with a metal hand file. This method is perfect for beginners as it affords you more control over the process and is usually more forgiving. However, sharpening a blade with a metal file takes the longest to do, needing about 50 strokes to get the blade sharp enough.

Here’s how to sharpen a mower blade by hand:

  1. Position the blade at the same angle as your mower blade (usually 30 to 45 degrees). You can consult your lawn mower manual to be sure.
  2. File in one direction going from the inside edge to the outside edge; never go back and forth. Make sure you can feel the file on the blade. If you can’t, then you probably aren’t applying enough pressure as you file.
  3. File the blade following its cutting edge. Even out nicks that you come across by filing the blade edge until it’s straight. Keep going until you see a shiny edge.
  4. Check the sharpness of the blade. It should only be as sharp as a butter knife. If it feels like you will cut yourself if you touch it, then it’s too sharp and you should immediately stop.
  5. Once one edge is done, take it out of the vise or clamp and turn it over. Repeat steps 1 to 4 with the other edge.

How to Sharpen a Mower Blade With a Drill Attachment

Sharpening a mower blade with a drill-powered blade sharpener is much faster than using a metal file. However, it’s not the best method for beginners. It’s much easier to make a mistake while sharpening a blade with this method as the plastic guide piece can get warped and make it harder to keep the sharpener steady.

Blade sharpeners have a flat plastic guide piece and a beveled sharpening stone. Here’s how to use one of these to sharpen your lawn mower blade:

  1. Attach the blade sharpener to your drill. Pull the drill trigger to ensure it’s attached securely.
  2. Get the blade sharpener into position. To easily remember how, think that “like goes with like.” In this case, the flat guide piece should be against the flat back side of the blade, while the curved cutting edge should be against the bevel of the grinding stone. If done correctly, the blade should be sandwiched perfectly in between the two pieces.
  3. While pulling the trigger, move the sharpener back and forth along the blade’s edge. Apply some pressure, but don’t go too hard. Smoothen out any nicks along the way. Give the blade a pass four to five times.
  4. Check the sharpness of the blade. It should be as sharp as a butter knife. If you feel like you’ll injure yourself from a simple touch, then it’s too sharp and you shouldn’t sharpen it anymore.
  5. Release the blade from the vise or clamp and turn it over to sharpen the other edge. Repeat steps 2 to 4.

How to Sharpen a Mower Blade With an Angle Grinder

Using an angle grinder is by far the fastest way to sharpen a lawn mower blade, taking a minute to sharpen both edges when you get very good at it. 

However, you need to have steady hands and careful control. It’s very easy to take off too much metal while sharpening the blade. This tool also spins so fast that the friction can overheat the edge of the blade, which ruins its temper. That means your blade becomes softer and weaker.

If you want to use an angle grinder to sharpen your mower blade, we highly recommend using a flap wheel with it. It’s more forgiving as it won’t take off as much metal. It’ll make your life easier. Here’s how to sharpen your blade with an angle grinder:

  1. Prepare a bucket of water. Your blade can overheat while being sharpened, so you’ll want some water to dip it in to cool it off.
  2. Position the blade of the grinder or the flap wheel so that it’s aligned with the cutting edge of the blade. Make sure you’re following the angle of the blade. You can consult your lawn mower manual to be sure about the angle.
  3. Move the grinder slowly, going from the inside edge to the outside edge. Don’t apply a lot of pressure and smoothen out any nicks. If the blade starts getting hot, dunk it in water.
  4. Check the sharpness of the blade. It should be as sharp as a butter knife; any sharper than that is too much.
  5. Take the blade out of the vise or clamp and turn it over. Sharpen the other edge by repeating steps 2 to 4.

Step 7: Check the Sharpness of the Mower Blade

Check the sharpness of the blade again by pulling a blade of grass over the blade. If it cuts cleanly, then you’re ready to check for its balance.

Step 8: Check for Balance

For the smoothest mowing experience, the mower blades should be balanced. Since sharpening removes metal from the blade, sometimes you end up with more metal on one side, which makes that side heavier. 

An unbalanced blade will wobble and vibrate much more while the lawn mower is being used. Aside from being quite annoying, it’s quite bad for your mower. The vibrations can damage the blade shaft and the bearings.

Using a blade balancer is the most accurate way to check if your mower is balanced. However, you also can use a nail on the wall or a screwdriver if you don’t have one of these on hand. Just be careful that the blade won’t fall on you. Here’s how to check your blade’s balance:

  1. Place the blade on the balancer or nail through the hole in the center of the blade. If you’re using a screwdriver, insert the screwdriver through the hole.
  2. Inspect your blade.
    1. Is it level? Congrats, your blade is balanced! You don’t have to do anything else. You can skip to Step 9: Reinstall the Blade.
    2. Does it drop or lean toward one direction? The side that’s dropping is heavier than the other. Sharpen that side again to remove some more metal. Check the blade balance again afterward.

Once your blade is balanced, it’s time to reinstall it.

Step 9: Reinstall the Mower Blade

lawn mower
Photo Credit: Pickpik

If you haven’t cleaned the underside of your mower’s deck yet, do so now. Make sure there isn’t any mud or grass clippings stuck under there.

Next, put the blade back onto the mower the right way around. Use the mark you made earlier as a reference. Then, use your ratchet and socket or your wrench to tighten the hardware securing the blade. Tighten it until it feels secure but don’t over-tighten. You can consult your lawn mower’s manual to check how tight it should be.

Now, it’s time to check if your mower is running properly. Reconnect the power source — spark plug, cord, or battery. Add fuel to your gas-powered mower if you need to. 

Start your mower, listen for strange noises, and feel for excessive vibrations. If nothing seems amiss, then pat yourself on the back. You’ve successfully sharpened your lawn mower blade! 

Pro Tip: Keep a spare lawn mower blade sharpened if you can. That way, you can just swap out the current lawn mower blade with a freshly-sharpened one if your blades become dull on you unexpectedly, like after hitting a rock.

FAQ on Sharpening Mower Blades

How Many Times Can You Sharpen a Lawn Mower Blade?

It depends. You can sharpen a mower blade as many times as needed as long as it’s in relatively good shape and as long as it’s not too thin.

How thin is too thin? If your mower is less than ½-inch thick, then it’s too thin and should be replaced.

Can You Sharpen a Mower Blade Without Removing It From the Lawn Mower?

Technically yes, you can sharpen a mower blade without removing it from the lawn mower. However, we really don’t recommend it. It’s not as safe and you can’t check the blade’s balance after.

Why Shouldn’t You Sharpen Your Lawn Mower Blade Too Much?

You shouldn’t sharpen your blade too much because a blade that’s razor-sharp will become dull faster. A blade that is sharpened too often will last much shorter, too.

Hire a Pro to Help Mow Your Lawn

Dull mower blades can cause your lawn to look brown, raggedy, or even patchy. It can even make your grass more susceptible to disease because it can’t heal properly. So, it’s important to sharpen them from time to time and when needed.
Don’t want to bother with sharpening your mower blades and maintaining your own lawn equipment? Hire a pro instead! LawnStarter can connect you with local lawn care pros who carry their own well-maintained equipment to keep your lawn green and clean-cut.

Main Image Credit: isuaneye / iStockPhoto / License

Janine Caayao

Janine Caayao

Janine Caayao has always been fascinated with growing plants, from fruits and veggies to bonsai trees and orchids. Now, she’s interested in urban gardening with her family. She loves finding new tips and tricks to keep their plants thriving.