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What Is the Best Way to Sharpen a Mower Blade?

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Well, with an estimated 63,250m² (163,812km²) of turfed grass in the US, you’re not alone in looking for an answer to this question. It’s not surprising, given the importance of sharp blades to the quality and health of your grass. But with a myriad of choices, the problem is you have to make a decision, and that’s always the hardest part.

So, what’s the best way to sharpen a mower blade? Here are a few options:

Now, although your budget is a primary consideration, there are other factors you’ll want to consider before deciding. In this article, you’ll find a host of information that’ll guide you towards determining which method of sharpening mower blades best suits you. Let’s start with some basics first.

Why Sharpen Mower Blades?

You’re probably thinking that the speed of rotation of the blades would be enough to cut the grass.

Well, in a sense, you’re right. But, if you look closely at grass that’s been cut with dulled blades and compare it to grass cut with sharp blades, you’ll notice a marked difference.

With sharp blades, the cut is clean, whereas if you’ve used a blunt blade, the cut end is uneven, as if the grass has been torn.

These torn edges take longer to heal than a clean-cut edge, exposing the grass to the risk of disease. Those rough edges will also dry up and turn brown, which is the last thing you want to see in your lawn.

So, now you’re clear why you need to sharpen your mower blades, let’s look at some preparatory steps.

How Do I Prepare?

Safety First — PPE

When doing any jobs around the home and garden, you can easily forget that danger lurks everywhere.

So, here’s what you’ll need: 

  • heavy-duty gloves
  • safety glasses
  • dust mask
  • ear defenders

Even though we’re talking about blades that may be blunt, there could still be sharper sections as wear can be uneven along the blade length. So heavy-duty gloves are a must.

Safety-glasses will protect your eyes from the grit and sparks that can fly around during the sharpening process.

A dust mask is crucial whenever you’re filing or grinding.

Ear defenders are a necessity when using most power tools because the noise levels can be literally deafening.

One thing you can be sure of is that you’ll never regret playing it safe.

Removing the Mower Blade

Remove Spark Plug

Before you remove the blade, you’ll need to disable the mower’s engine. This will prevent the possibility of the engine starting and rotating the blade.

All you need to do is disconnect the rubber wire that’s attached to the spark plug. Then, secure it in a position that will prevent it from snapping back into contact with the spark plug.

Tip the Mower to Access the Blade

Before you tip your mower to access the blade, you’ll need to think how best to do it to avoid problems later.

You want to avoid oil leaking from the engine into the carburetor and air filter. If that happens, you’ll have to clean the carburetor and air filter.

So, firstly, you’ll need to locate the carburetor and air filter. Most often, just look for a black plastic housing on the side of the engine. But, if you’re unsure, follow the throttle cable because it’s connected to the carburetor.

Once you’ve found them, just tip the mower onto the opposite side. That will leave the carburetor and air filter facing up.

But, before you tip the mower, have an old rag handy to cover the cap on the gas tank. Most caps are vented with a small hole to allow air into the gas tank as the gas level drops. When you tip your mower to access the blades, gas may leak from that hole.

It shouldn’t be much, but you’ll need to clean up any spillage, and why create more work for yourself?.

Remove the Mower Blade

OK, you’re mower’s on its side.

Before you do anything, give the underside a good clean, removing any debris and dirt.

You’ll see the blade is secured with a single bolt. Remember, you’re dealing with a component that rotates, so when you try to loosen the bolt, the blade is going to turn. You’ll need to secure the blade so that it’s locked into position.

You can buy a purpose-made tool that will lock the blade in place. However, if you don’t want to incur the expense, just use a sturdy block of wood to wedge the blade in position.

Next, a common problem you’ll encounter is the bolt can be tight and hard to turn. So, you’ll need a ratchet socket wrench that fits your bolt and penetrating oil, like WD-40.

If your bolt has seized, you may find the extra leverage from using a breaker bar will make the task easier.

Preparing the Blade for Sharpening

Mark the Blade

You know how it is, especially if you don’t do something very often. When you’ve removed the blade, it’s all too easy to forget which way round it went when you come to refit it.

If you reinstall it the wrong way round, all your good work will be wasted, because the blade won’t cut. You can avoid this by marking one side with something like a permanent marker.

Clean and Inspect the Blade

You should be able to remove any built-up deposits of plant and other material from the blade with hot soapy water.

Once the blade is dry, you can check if there’s any rust on it. If so, use a wire brush to remove the rust.

Next, check for any damage to the blade. As you’ll know, mower blades aren’t just cutting grass. Often, they’re encountering other tougher material, including stones. All of these can cause nicks and gashes in the blade, or can even bend or crack it.

For most minor nicks, you may be able to grind those out later. However, if the damage is significant, you should consider replacing the blade.

Keep the Blade Cool While Sharpening

If you choose one of the power tool sharpening methods, the friction will heat the blade. So, you’ll need a way to cool it down because heat softens and weakens the blade, making it prone to damage.

You don’t need anything fancy, just a good old bucket of cold water. All you have to do is plunge the blade in the cold water, and dry it off before resuming.

How to Sharpen a Mower Blade

Before discussing the various methods to sharpen your mower blade, you’ll need to know what you’re aiming for. So, how sharp is sharp?

What you don’t need is a razor-sharp blade. It’s a bit counter-intuitive because you’d think for a clean cut, the sharper, the better.

However, if the blade is too sharp, the thinner edge is more prone to damage. This could be costly, as you may end up having to replace the blade sooner than otherwise necessary.

A phrase commonly used is that a mower blade should be butter-knife sharp.

So, now that’s cleared up, let’s look at some of the sharpening methods you can use.

Hand-held File

Equipment Needed

You’ll need:

  • a vise to hold the mower blade  
  • a mill bastard file 
  • a file card to clean debris from the file

Steps: 

  1. Secure the mower blade in the vise. The cutting edge of the blade should be facing upwards.
  2. Sharpen the mower blade by pushing the file along the cutting edge. You should only file in one direction, on the push stroke, from the outer edge of the blade inwards. Go the other way, and you risk the edge of the blade curling. Move along the blade for the full length of the original factory bevel.
  3. Ensure that you follow the angle of the blade. When you have the mower blade in the vise, you’ll see the angle of the cutting edge. Just rest the flat side of the file on that angle with each stroke. Try a couple of light passes over the blade, and you’ll soon get a feel for the correct angle.
  4. Clean the file regularly. Use the file card to clear debris from the file to maintain its effectiveness.
  5. Remove the burr. Sharpening on one side of a blade produces a rough edge where the sharpened side meets the unsharpened side. In the case of your mower blade, you’ll see it on the underside of the blade. You can remove the burr with the file, using gentler strokes.
  6. Repeat for the other end of the blade

Although this method is manual, it gives you a high degree of control over the process. Of course, it’s also an inexpensive option.

Rotary Sharpener Drill Attachment

This is another cheap option if you have a hand-held power drill. The attachment fits into the drill like a drill bit. An example of this is the Oregon Mower Blade Sharpener. It’s a flat piece of plastic with a sharpening stone in front of it. The gap between them is where the mower blade goes.

Equipment Needed

You’ll need:

  • a vise to hold the mower blade
  • a power drill
  • a blade sharpener drill attachment
  • a file

Steps: 

  1. Secure the mower blade in the vise. The cutting edge of the blade should be facing upwards.
  2. Slot the sharpener onto the blade. The underside of your mower blade sits flat against the plastic guide, while the cutting side of the blade will be facing the beveled surface of the stone.
  3. Start the drill and slide along the length of the mower blade and back again. The bevel of the stone matches the angle of the blade. Check the mower blade after a few strokes and repeat, if necessary.
  4. Remove the burr. See step 5 above.
  5. Repeat for the other end of the blade.

So, this method requires less effort than using a file, and it’s also relatively inexpensive. It’s worth giving it a go as you’re not risking much if it turns out that it’s not right for you.

Angle Grinder

Next up is the angle grinder. What we’re talking about here is something like the Dewalt Angle Grinder Tool.

As it’s more costly than either of the previous two options, you may want to give those a try first. However, if you already have one handy, and want to have a go, here’s how.

Equipment Needed

You’ll need: 

  • a vise sturdy enough to hold the mower blade in place
  • an angle grinder

Steps: 

  1. Secure the mower blade in the vise. The cutting edge of the blade should be facing upwards.
  2. Lightly pass the grinder over the cutting edge of the blade, moving in one direction only. It may take a couple of passes for you to feel the angle of the mower blade, but that’s OK as you won’t be applying too much pressure.
  3. Ensure each pass covers the extent of the original bevel.  
  4. Remove the burr. See previous methods.
  5. Repeat for the other end of the blade.

If you like this method, but need some help maintaining the angle, there’s a handy device you can use in conjunction with your angle grinder. It’s called the All-American Blade Sharpener.

The name’s a little confusing, as it’s not a sharpener itself. It’s a jig with an angled arm that attaches to your grinder so your grinder can only move along a set path. The other part is a vise connected to the arm and holds your mower blade at a fixed angle. The arm guides your grinder, so you’re grinding along the same line and at the same angle throughout.

This device makes the angle grinder method easier but adds to the cost.

Bench Grinder

Let’s move on to the bench grinder. An example of this is the Dewalt 8” Bench Grinder. This piece of kit is more costly than the previous methods discussed. But, if you don’t mind the expense or the other methods aren’t working for you, here’s how to do it.

Equipment Needed

Here’s what you’ll need:

  • a bench grinder

Steps: 

  1. Using the rest plate of the grinder for support, run the mower blade against the grinding wheel. Slide the cutting side of the mower blade across the grinding wheel slowly.
  2. Move the blade in one direction, maintaining a steady angle. Again, you need to follow the angle of the original bevel.
  3. Remove the burr. See previous methods.
  4. Repeat for the other end of the blade.

This method is quick but may be hard to master at first.

It’s also an easy way to grind out nicks on the edge of the mower blade. To do this, you’d hold the edge perpendicular to the grinding wheel.

So, if the edge of your mower blade is severely damaged, a few passes across the grinding wheel should improve its condition.

A variation on the bench grinder is a grinder made especially for sharpening blades, such as the Oregon 88-205 Blade Grinder.

This is moving up yet another price level. So, you’d probably only be looking at something like this if you were mowing lawns as a business.

The difference between this and a bench grinder is that the mower blade rests on a flat plate and slides under the grinder wheel. So you move the blade along the plate to sharpen. As the blade is supported by the plate, maintaining a uniform angle is easier.

After Sharpening

Balance the Blade

Balancing your mower blade is a crucial step if you want to avoid the risk of damaging your mower.

So, once you’ve sharpened your blade, use a blade balancing tool like the Oregon Lawn Mower Blade Balancer to check the blade is evenly balanced.

Just set the blade on the balancing tool using the center hole in the blade. If the blade is balanced, it’ll be horizontal.

If one end is dipped, you’ll need to file or grind more metal away to balance it out. The additional material should be removed from the underside of the blade, not from the cutting side.

You can balance your blade even if you don’t have a balancing tool, by using a nail or dowel in a wall.

An unbalanced blade can cause your mower to vibrate badly, and this can damage other moving parts. So, you shouldn’t skip this step and, really, there’s no reason to, given it’s so easy and inexpensive.

Once your blade is balanced, reinstall it, the right way up, just hand tightening the bolt.

How Often Do I Need to Sharpen a Mower Blade?

It will depend on how often you use your mower. For regular domestic use, say, once a week, you should only need to sharpen once or twice in a mowing season.

If you use your mower more frequently, then you’ll need to keep a closer eye on the blade. Check it during and after each use. When you notice a change in the quality of the cut, that’s the time to do it.

Do I Need to Remove the Blade From the Mower Before Sharpening?

It’s possible to sharpen your mower blade without removing it from the mower if you’re using methods 1 to 3 above.

However, you’d need to ensure that the blade is immobilized to prevent it from rotating, especially if using an angle grinder. Otherwise, it’ll be dangerous and hard to maintain the angle of the cutting edge.

The confined space you’d be working in may also affect the standard of the overall result. You may find it challenging to get an even pass over the blade’s length, which could affect the cutting quality

But, unless you’re just doing a quick touch-up that doesn’t involve removing a great deal of the metal, there’s a problem with not removing the blade.

That is, you won’t be able to balance the blade, and, as mentioned above, that’s a crucial step in the process.

So, generally, it’s best to remove the blade.

Final Thoughts

So, what’s the best way to sharpen your mower blade? The truth is, there’s no single answer. It comes down to whatever works for you. Whether that’s determined by budget, ease of use, time available, or end result, you decide.

Hopefully, the information here has given you enough to go on to make that decision.

If you’re still unsure, start with the cheapest option. If necessary, you can then work your way up the cost scale until you find the method that you’re happy with.

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