How to Sharpen Lawn Mower Blades?

You’ve probably heard of the adage ‘all work and no play make Jack a dull boy.’ Guess what! The same applies to your lawn mower blades. After long-term usage, its blades slowly become dull.

Continuous use will make them tear your grass instead of cutting it smoothly. This might result into a ragged look and make your lawn more susceptible to diseases. We’re sure that’s not what you want, right? 

You should purpose to sharpen lawn mower blades at least twice every season for a healthy lawn. Fortunately, sharpening lawn mower blades doesn’t require loads of skills. You just require a few tools, some elbow grease and before you know it, you have rejuvenated lawn mower blades.

However, sharpening lawn mower blades is much easier when you know what you’re doing. We’ll give more insights on that, but first.

Why Sharpening a Lawn Mower Blade Matters?

Sharpening a Lawn Mower Blade

A blade rotating at a speed of 180 mph or more doesn’t need to be very sharp to cut grass, isn’t it? You could be right. However, there’s a big difference in a grass cut from a sharp lawn mower blade and a dull one.

  • A sharp lawn mower blade slices smoothly through grass thus allowing it to grow in a healthier manner.
  • Sharp lawn mower blades give your lawn a professional finished look. This is so evident in species like Fescue that require frequent cutting.Mowing Lawn with a Lawn Mower
  • Sharp blade prevents your grass from turning brown, looking ragged and burnt.
  • A sharp blade lets you complete your lawn-cutting faster and easily. A sharp lawn mower blade doesn’t only help cut the grass clean but also reduces the mowing time.
  • Grass cutting with a sharp blade allows the grass to heal and recover faster.

Undoubtedly, you’ve spent loads of time and money growing, fertilizing, watering and even controlling weeds on your lawn. Why not spend a few minutes to sharpen your lawn mower blades. Trust me, your lawn will thank you for it.

How to Sharpen Lawn Mower Blades?

Lawn Mower Blades


Don’t be the last-minute shopper and have these materials ready ahead of time.

  • Gloves
  • Face mask
  • Hearing protectors
  • Lawn mower blade
  • Lawn mower blade grinder
  • File
  • Spark plug socket
  • Vice
  • Rags
  • WD-40 lubricant

Once you’re set with all the necessary tools, proceed as follows.

Part 1: Prepare the Blades for Sharpening

  • Remove the spark plug and disconnect the power source. Always start by disconnecting these before disassembling the lawn mower. This ensures that the lawn mower doesn’t accidentally start while you work on it. To disconnect the spark plug, remove the prominent wire on the front or side of the lawn mower engine. Once this is done, the engine can’t start. You may need to tape it to be sure it doesn’t flop back with the plug.Lawn Mower spark plug
  • Turn the lawn mower upside down and let its carburetor and air filter face up. The carburetor can be easily identified through its throttle cables that run in and out of it. The mower is turned on its side so as to enable access to its blades. It also prevents the engine oil from spilling into the air filter and carburetor. Additionally, to prevent the spillage, you may need to operate the lawn mower until its gas is finished or empty its oil to a different container. Use a rag to clean any drips. In case you aren’t sure of where the air filter and the carburetor are located on the lawn mower, check the manual or consult the manufacturer.Turn the lawn mower upside down
  • Put a mark on the downward-facing part of the blade. Simply stick some masking tape, grease pen or a dot of spray paint on the blade’s part that is to be marked. Doing this helps you ensure that you don’t re-install the lawn mower blade upside-down. Mark you this is a very common mistake. If it happens, the blade can’t function regardless of how sharp it is. As such, get it right at the start by putting the right markings. This prevents you from going nuts trying to figure why your lawn mower isn’t functioning.
  • Loosen the blade’s fastening bolts to remove the blade. Most blades are secured with a bolt at the center. As such, it may be difficult to use a ratchet or wrench because it will turn with the tool. To avoid this, immobilize it before you start loosening the bolt. Avoid using your foot for this. Use a vice to immobilize the blade while you loosen its bolt. This will also give you lots of leverage to loosen very tight bolts. In case of rusted or stuck bolts, apply a squirt of the lubricant. After removing the blade, put the lawn mower upright until you’re ready to re-install its blade.Loosen the blade’s fastening bolts
  • Wipe out any grass clippings and rust. After removing the blade, clean it to remove all grass clippings and grime that could have accumulated over time. All you need to do this is a gloved hand or a rag. However, if the dirt had accumulated, a little soapy water and a hose will be handier. 

Part 2: Sharpening Lawn Mower Blade

There are varied ways you can sharpen lawn mower blades. We’ll discuss them and then the choice on which method to use will depend on your preference.

Method 1: Sharpening By Hands Using A File


Sharpening Lawn Blade By Hands

  • Clamp the blade at your work station using a vice. Be keen to clamp it in a way and place that is convenient for you to work on it. You can place some pieces of newspapers under the workbench to catch stray metal filings and for easy cleanup.
  • File the blade. After clamping the blade conveniently, run the metal file over its cutting edge. Stroke it from the outside and inside edge of the blade until a clean shiny edge appears. Turn it and repeat that process on the other edge. You may need to wear a face mask to prevent the chances of metal particles and airborne dust from entering your lungs.
  • Follow the factory’s specified angle of sharpening. Ideally, the blade angle should be about 40-45 degrees. However, that’s not always the case. Therefore, follow the manufacturer’s instructions on the required sharpening angle, if any. Importantly, lawn mower blades shouldn’t be razor-sharp, a butter knife’s level of sharpness is enough.
  • Re-install the sharpened mower blade. Start by applying some lubricant on the main bolt to deter it from rusting. Hoping you had marked the downward-facing side as directed, mount it back on the mower, and put any washers and then the bolts. Tighten the bolt and check its tightness by turning the wrench.

Method 2: Sharpening Lawn Mower Blades with a Machine

If sharpening mower blades by hand with a file isn’t your thing, using a machine-bench grinder may be necessary. This is also required where the blade has minor dents and cracks.


  • Wear protective clothing. Observe common sense and start by wearing gloves, eye protection and long sleeves. This ensures that the bench grinders don’t fling any debris or sparks at you. Such materials at their very high speed could cause injuries if you don’t have proper protection.
  • Using the bench grinder. Sharpen the mower blades forth against the wheels of the grinder. As with the previous method, follow any manufacturer’s guidelines on the angle of the blade’s level.Using the bench grinder

Method 3: Use of a Belt Sander

For this alternative method, the above basic principle applies. 

Use of a Belt Sander

  • Invert and let the belt sander’s belt face up. 
  • Set the trigger switch to the ‘on’ position.
  • Set the lawn mower blade at an angle and rub it against the rough sandpaper.
  • The lawn mower blade gradually sharpens through friction.

 Tips During and After Sharpening Lawn Mower Blade

  • Minimize heating. The high friction that occurs when sharpening mower blades can make them overheat. This excess heat can make them become weak as it become sharper. Avoid this by quenching it frequently during the process by dipping it in a bucket full of water to let it cool down.Minimize heating with water when you sharpen a blade
  • Wipe it dry. Before resuming the sharpening process after the water dipping, use a rag to wipe it dry. This reduces chances of the blades sliding out, something that could result into untold injuries.
  • Check its weight before mounting back. After sharpening and right before re-installing, hang it on a nail to check blade balance. This helps you know whether all sides have been sharpened. See the side that dips and the file more on the opposite side until it remains horizontally balanced.horizontally balanced lawn mower blade
  • Habit of always keeping the lawn mower blades sharp. You may need to dedicate some sharpening tools for lawn mowers only or keep a spare blade set and use it when the other one gets dull. Basically, let there be zero excuses for not having a sharp lawn mower blade.
  • Replace lawn mower blades that have deep cracks or dents. If they’re beyond repair, sharpening won’t sort their issues. Replacement is a quicker and easier option.

Wrapping It Up…

We told you that sharpening mower blades takes little effort, didn’t we? Also, we deem it an awesome DIY project that anyone can handle. Regardless of which method you opt for, always guard yourself by putting on proper protective equipment before and in the process of sharpening lawn mower blades.

Which of the above methods worked most consistently for you? We would love to hear from you in the comments section below.

About Jennifer Igra

Growing up in Brooklyn, New York City known for it’s green gardens. Jennifer, a 30 year old gardener and green living fanatic started Igra World to share her gardening journey and increase gardening awareness among masses. Follow Igra World to improve your gardening skills.

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