How To Sharpen A Lawnmower Blade

If your lawn isn’t looking as vibrant as it used to after a cut, you may want to take a look at your lawn mower’s blade. Even regular use will dull your mower’s blade, and that’s not counting any unexpected contact with dirt, wood, or sand that can damage the blade even more. A sharp blade will save you time mowing. It’ll also ensure a cleaner cut, which is better for the health of your lawn. You can have your blades professionally sharpened, but why not give it a try yourself?

There are by-hand and mechanical methods you can use to sharpen your mower’s blades, and we’re walking you through both today. Keep reading to learn the ins and outs of lawn mower blade sharpening!

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When Should I Sharpen My Lawn Mower’s Blade?

There are a few telltale signs that your mower’s blade needs a good sharpening. Inspect your lawn and your mower after every cut (let the equipment cool down first, of course). You’re on the lookout for the following signs:

• An uneven cut. If your lawn is looking uneven after mowing, the blade is probably dull.
• Jagged grass blades, often with browning edges. Check out some individual grass blades after a cut. If they look like they’ve been torn rather than sliced, your blade is probably dull. A jagged cut can cause your grass to brown.
• Blunted mower blades. A sharp blade is obvious, coming to an angled edge. Dull blades will be slightly blunted.
• If the blade has seen 25 or more hours of use, it probably needs to be sharpened. Most mower blades are sharp for 20 hours of use. Depending on the size of your yard and how long it takes to cut, that could be 40 sessions or it could be 10.

How To Sharpen A Lawn Mower Blade

There are a few different ways to safely sharpen your mower blades. We’ll review them in the next sections.

Basic Tips

• For safety, always wear work gloves, safety goggles, and long sleeves when removing,  installing, or sharpening your lawn mower blade. If you’re using a machine to sharpen your blade, wear ear protection as well.
• You can sharpen by hand with files and abrasives, or you can use a blade sharpener, bench, or angle grinder.
• Before sharpening, thoroughly examine the blade for signs of serious damage. If it’s cracked, dented, very thin, or badly chipped, replace the blade instead.
• You don’t want your blade to be razor sharp – that just makes it more dangerous for you to handle. It’ll also dull more quickly. Instead, aim for a blade that’s about as sharp as a butter knife.
• As with all potentially dangerous DIY tasks, if you aren’t completely confident in your ability to sharpen your mower’s blade safely, don’t hesitate to use a professional blade sharpening service or simply replace the old blade with a new one. Check out our guide to replacing lawn mower blades for more details!

How to Remove a Lawnmower Blade

1. Start by setting the mower on a flat, stable surface. You may want to set something like a mat down on your workspace first to protect it from any accidental spills.
2. If your mower has a grass bag, remove it.
3. Ensure the mower is entirely unpowered. Unplug it, remove the battery, and/or disconnect the spark plug wire from the machine before going any further. This is vitally important! Do not proceed to the next step while the mower could still potentially turn on. You can generally find the spark plug on the front of the mower. Just pull the boot off to disengage it. Make sure the boot is out of the way and cannot touch the spark plug.
4. If you have a gas mower, you may need to drain the fuel tank. If you don’t, fuel will likely spill out.
5. Tip the mower back. You can turn it on its side or push it back with the handles on the ground.
6. Jam the blade so that it doesn’t turn. Fixing a pair of vice grips to the mower’s deck will block the blade. Inserting a block of wood into the deck to catch the blade also works. If you don’t do this, the blade will simply turn when you’re trying to remove the bolt.
7. Remove the bolt and washers holding the blade in place. A ratchet will provide better leverage than a wrench, which is important because the bolt may be somewhat difficult to remove if the mower has seen a lot of use. Bolt giving you problems? If the bolt is stuck, you can try using a breaker bar with your ratchet to create more leverage. Striking the bolt with a hammer can help to dislodge corrosion on the bolt, making it easier to remove. However, if you do this, wear eye protection. As there could be debris.
8. Remove the blade. Make note of how it was installed. You may even want to use spray paint or a paint marker to mark it so you remember how to put it back once it’s time to reinstall.
9. Inspect the blade and ensure it’s clear of grass, dirt, and other debris before sharpening it. A wire brush should be enough to get it clean, but if the grime is particularly stubborn, sandpaper should do the trick.

Sharpening A Mower Blade By Hand

Sharpening by hand takes longer than using a machine, but you’re less likely to risk damaging the blade by oversharpening or overheating the metal.

1. Safety first! Wear gloves, protective eye gear, and long sleeves to shield yourself from metal shavings. You may also want to wear a face mask or respirator so that you don’t breathe in any dust.
   
2. Clamp the blade into a vice so that it is secure. Make sure you’ve positioned it so that it is easy to work with.
3. Sharpen the blade with a 10-inch file, holding the file at about a 45 degree angle. Start from the inside edge of the blade and move to the outside. Do not saw back and forth. You’ll want to work until you have a clean, shiny edge. Once you’ve achieved this, flip the blade and repeat the process.
   • Follow the angle of the blade edge.
   • As mentioned, you’re aiming for the thickness of a butter knife.
   • If you aren’t feeling the file’s teeth on the blade, apply a bit more pressure.
   • If applying the proper amount of pressure, this shouldn’t take more than 50 strokes and take as few as 10.
4. Once both sides are sharpened, the blade can be reinstalled on the mower. 

Sharpening A Lawnmower Blade With A Grinder

You can use an angle grinder fitted with a flap disc or grinding stone disc to sharpen your blade. Machine sharpening is much faster than sharpening by hand, but you do run the risk of overheating the metal.

1. Safety first! Grinders fling sparks and metal shavings, so wear long sleeves, gloves, and eye protection if you plan on sharpening your mower blade this way.
2. Make sure your mower blade is properly and securely clamped in a vice.
3. With the grinding disc perpendicular to the thin edge of the mower blade, run the grinder back and forth on the blade slowly but constantly. You’ll want to even out any nicks or rough spots.
   • As with hand sharpening, follow the angle of the edge.
   • Once one side is finished, flip the blade and repeat the process with the other side.
   • This process goes by very quickly, so pay careful attention and stop the grinder to check your work as needed.
4. If at any point the blade gets too hot to touch, stop. You can quench the heat in a bucket of water. Take care, because overheating the blade can damage it or leave it brittle.
5. Once properly sharpened and completely cool, you can reinstall the blade on your mower.

Sharpening vs Replacing Lawn Mower Blades

Mower blades are durable and most standard push mower blades can generally stand up to one or two sharpenings before needing to be replaced. You should be inspecting your mower’s blade regularly to ensure that your equipment is safe to use and you’re effectively cutting your lawn. If you aren’t sure whether to sharpen or replace your mower blade, here are some things to watch out for:

• If you inspect your blade and find chips, dents, or cracks in the metal, skip the sharpening and just buy a new blade. Sharpening won’t fix that kind of damage, and blades like that are generally at high risk of breaking entirely, which is a huge safety hazard!
• If your blades are especially thin, it’s time to replace them. A blade worn too thin has a greater risk of breaking and causing serious injury. Definitely change out the blade if parts of it have worn down to paper thinness!
• If you’ve sharpened your blade multiple times and it’s dulled again, consider replacing it. Blade durability does vary. Standard home use push mower blades can typically stand up to one or two sharpenings, while some landscapers report sharpening the same blade much more than that. However, sharpening weakens blades, making them more brittle and increasing the risk of breaks.

In general, you should never use a mower if your blades aren’t in good shape. If you notice any cracks, bends, or severe chipping or thinning, delay that cut until you can replace the old blade with a new one. If your blade is looking a little too rough to sharpen, why not check out our options at AppliancePartsPros.com?

Wrapping Up

On average, you’ll probably need to sharpen your mower blades about twice a season, and with our guide, you should have a better understanding of how it’s done! Now that you know how to inspect and sharpen your mower’s blades, why not check out how else AppliancePartsPros.com can help. We’ve got tips, tutorials, and new OEM parts for all of your DIY lawn equipment and home appliance upkeep and repair projects!