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How To Sharpen Lawn Mower Blades

There is no denying, a blunt lawn mower is a bad lawnmower.

Once blades lose their sharpness a lawn mower loses its effectiveness.

Luckily if you trying to learn how to sharpen lawn mower blades you are in the right place. So lets crack on with our guide.

Lawnmower blades are bound to become dull over time especially if you mow your lawn very often.

As the blade gets dull, your mower will fail to produce the same excellent results that it used to before and it will gradually become a pain to use.

But how can you tell that your mower has a dull blade?

I am going to walk you through the whole process.

How To Tell If Your Lawn Mower Blades Need Sharpening

The clearest signs will be visible on your lawn after you trim it.

A dull lawnmower blade will be unable to cut grass smoothly and its blunt cutting edge will instead forcefully tear off the top edges of grass, causing rough cuts.

The result?

Your lawn will have unevenly-cut grass with several missed patches.

If you fail to act fast in fixing a dull blade, there will be unpleasant consequences such as;

#1 Damaged Lawn

Instead of making clean cuts, a dull mower blade basically shreds the grass it comes into contact with and the result is usually a rugged-looking lawn.

And that’s not all, this shredding action also has a negative effect on the health of the grass. Grass cut using such a blade becomes frayed and takes a longer time to heal.

What follows is the emergence of bare or brown patches within a previously lush green lawn.

#2 Mechanical Damage On The Lawnmower

A dull blade will strain to slice through grass and this can lead to excessive vibrations as it spins.

Increased vibrations create a lot of stress on the rotating components within the mower such as the shaft and the bearings and this added strain can eventually cause mechanical damage.

#3 Requiring More Time To Perform Routine Tasks

A dull lawnmower is bound to miss some patches when you use it to trim your lawn.

To achieve an even trim, you may therefore have to run your mower over your lawn several times and this will be an exhausting and time-consuming affair.

Dealing With A Dull Blade

The easiest way to deal with a dull blade is to simply get rid of it and replace it with a new one. But opting to replace the mower blade every time it gets dull will be similar to throwing away your phone battery every time it runs out of power; it is doesn’t make any economic sense, right?

You are dead right!

There are some instances however when the blade is in such a dire state that replacing it is the only viable option. These will be discussed later in this article.

Sharpening a lawnmower blade is not a complicated task by any means. In fact, even with no prior experience, it can be done by anyone in less than an hour. You will have no trouble if you have the right tools and do everything as per the instructions.

This is important:

You should be extremely cautious when handling mower blades. They can cause terrible injuries if handled incorrectly.

This article will provide you with an easy but safe way of sharpening your mower blade at home.

Sharpening A Lawn Mower Blade

What You Will Need

  • A hand-file or a bench grinder
  • A blade balancer
  • A vice or clamp
  • A long-handle wrench
  • A workbench
  • Lubricant (preferably penetrating oil) – To be used in loosening nuts that are stuck or badly rusted.
  • A pair of tinted goggles – These will only be necessary if you intend to use a bench grinder to sharpen the blade. These goggles will protect your eyes from scattering iron filings.
  • A permanent marker or a can of spray paint
  • A source of cool water ( preferably a tap or a hose connected to a tap ) – This is if you intend to use a bench grinder to sharpen the blade. The reason for this will be explained below.
  • A dust mask – You don’t want any iron filings wafting into your lungs.

Step One – Detaching The Blade

Before removing the blade, you will have to disconnect the spark plug to prevent the mower from accidentally starting.

If you are not sure where the spark plug is located or how to disconnect it, refer to the owner’s manual that came with the lawnmower.

NEVER skip this part as:

Failure to disconnect the spark plug can cause the mower to start without warning as you work on it and you may lose a few fingers or even a limb on the process. 

After you have the spark plug detached, you can then flip the mower on its side to access the blade. This blade is usually attached to the rotating shaft by a tightly screwed nut at the center. Use a wrench to loosen this nut and remove the blade.

A little tip:

The longer the wrench handle, the less effort you will require. Every now and then you may encounter a nut that refuses to bulge as it may have been screwed too tight or is too rusty.

In such cases, you will need to apply a little amount of penetrating oil to lubricate the joint and make it rotate more easily.

Then:

Once the blade has been detached, you can use a permanent marker or a little spray paint to indicate the side which should face up when the blade is being placed back.

The lawnmower won’t cut through anything if the blade is placed with the wrong side facing up. You can skip this part if you can comfortably tell the top part of the blade from the bottom part.

Step Two – Sharpening The Blade

Using A Hand Saw

Use the clamp to securely hold the blade in position on the workbench before you begin sharpening. Run the file along the cutting edge of the blade from top to bottom. While doing this, the file should be slanted on the blade in the same angle as that of the cutting edge at all times.

That is because:

This is the angle set by the lawnmower’s manufacturer and it should be maintained to ensure optimal performance. A few full strokes should be enough to give the cutting edge a shiny appearance which will restore its sharpness.

The blade should never get too sharp as this will cause it to get nicked more easily. You should aim to achieve a level of sharpness similar to that of a butter knife.

Using A Bench Grinder

Using a bench grinder will get the job done much faster. A grinder can also easily even out any nicks or dents along the cutting edge with minimal effort.

The downside to using a grinder is that the blade can easily overheat due to the increased friction.

Why’s that?

Well mower blades are made of soft steel which can considerably lose its hardness when it is heated to a high temperature. This is why you will need to have cool running water nearby when using a grinder.

A bench grinder will also send hot iron filings flying through the air and you will have to wear goggles and a dust mask to protect yourself from injury.

But one thing is for sure:

When using a grinder, a vice won’t be necessary. You will instead place the grinder on the workbench and guide the cutting edge of the blade against it in a back and forth motion using your hands.

To ensure that the blade doesn’t get damaged, rinse it in cold water every time you feel its temperature rising. You will also need to ensure that the angle of the cutting edge is maintained as you sharpen it.

Step Three – Checking The Blade’s Balance

A mower blade is divided into two halves with the gap where the bolt is attached being the center.

Want optimal performance?

Then both halves have to be of equal weight to ensure no wobbling occurs at it spins. After extended periods of use, it is common for one half to wear disproportionately compared to the other.

After sharpening the blade, you will need to mount it on the blade balancer to check if both sides are of equal weight. If the blade tilts to one side, you can use your file or grinder to shed off some of this extra weight by sharpening this side again.

I am not going to lie:

This requires a little patience since you may have to repeat this several times before achieving the right balance.

Step Four – Attaching The Blade

At this point, the blade should be sufficiently sharp and well balanced. You can now safely bolt the blade back in place using a wrench.

In doing this, ensure that the blade is positioned exactly as it was before you detached it, with the right side facing up. The bolt should also be screwed into place as tightly as possible.

You can then flip the mower back into an upright position before attaching the spark plug and taking it for a test run.

Bingo!

Step Five – Replacing The Blade

Mower blades have a limited lifespan. This depends on how frequently the lawnmower is used and the level of care or neglect it is subjected to.

But:

There are some instances where a blade is too worn out and even sharpening it cannot restore its cutting ability.

In such cases, the blade has to be replaced with a new one. You will need to replace the blade if;

  1. It has visible cracks or is bent: A bent or cracked blade can easily break apart while it is being used. Lawnmower blades spin at high speeds and if a blade splinters it will be propelled outward like a projectile which is something you never want to encounter.
  2. If your blade wobbles or vibrates excessively despite being tightly bolted in place, it might be bent.
  3. It has too many nicks and dents along its cutting edge.
  4. The cutting edge has been filed too many times and has become very thin.

Safety Tips

Remember:

  • Before you attempt to detach the blade or fix anything under your lawnmower, always make sure that the spark plug has been disconnected.
  • Never try to fix a bent or cracked blade. The risks involved in doing so are too grave. You are much better off replacing it altogether.

Extra Care Tips For Your Lawnmower Blade

Finally:

  • Lawnmower blades need to be sharpened regularly. The recommended frequency is twice per season.
  • Before mowing your lawn, try to pick up any visible pebbles and twigs that can potentially nick the sharp edge of your blade. This will save you the hassle of having to deal with a dull blade after every few cuts while also extending the lifespan of the blade.
  • After using your lawnmower, clean the debris from the blade and wipe off any moisture before storing it to ensure that it doesn’t undergo any rusting while in storage. This should always be done after disconnecting the spark plug.

USEFUL RESOURCES

About The Author

Steve Mann

Steve is a one time gardening hater turned into gardening obsessive. This was all thanks to going to University where a two year stint spent transforming the previously horrific garden of the student house he lived in left him addicted to all things horticultural! Now with a new house in tow and due to some fortunate circumstances he is free to test out a whole host of gardening equipment. Find out more about Steve or drop him an email at steve@suaveyards.com.

4 Comments

  1. Chris Jones

    Great site on lawn tips and how to sharpen my lawn mower blade. I can tell it when the tips of my grass turn brown. I am so lazy though wish someone came around to do a tune up on lawnmowers. I do love having a great looking lawn though.

    Reply
    • Steve Mann

      Thanks Chris, it is easy to postpone the job – I am guilty of that! But I try and sharpen my mower blades twice a season, will make your lawn look EVEN better! Steve

      Reply
  2. Matteo

    Hi Steve,

    Great post! Very informative!
    I am currently writing about sustainability, and it is always great to see more solutions out there preventing people on over-consuming or overproducing stuff like lawnmowers and their blades.

    I also believe I am one of those people who are scared that if they mess with machinery it will never work again once I put it back together!

    Your post is definitely giving me more hope! I will definitely back for more info when it comes to yard work!

    All the best,
    Matteo

    Reply
    • Steve Mann

      Thanks Matteo, glad I was able to give you hope! Don’t hesitate to drop me a line if you have any questions, I’d be only too happy to try and help 🙂

      Steve

      Reply

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About Me

SteveHi, my name is Steve and I am the founder and editor of Suave Yards.

Once upon a time I was a complete gardening newbie, but over the last few years I have learnt a lot about yard care – all stemming from taking over a mess of a garden when I started at university!

My team and I have put together a comprehensive series of reviews and guides to help you create the perfect garden.

So please take a look around!