Is your mower not cutting like it used to? Torn grass? Lawn issues? A rattling deck? If so, then it could be time to sharpen your mower blades. I’ve learned over the years that you can get back that “new blade cut” by spending just a few minutes with a couple of tools and techniques. I’m going to share my favorite methods on how to sharpen a mower blade. I’ve compiled my best tips and tricks and created a step-by-step guide that you can follow to get your lawn mower blade cutting like new again.
Knowing When It Is Time to Sharpen Your Mower Blades
Look at the cut your lawn mower blade makes and the blade edge. These two very simple methods will tell you if it’s time to sharpen your blade.
If the grass is not being cut cleanly, it’s likely the blade is not sharp. And if the mower blade feels dull or has dents, it’s not sharp either. It won’t take you long to make this “diagnosis”.
So now that you have identified that your blade is dull, let’s dig a little deeper into how to sharpen a mower blade and what the process is. There are a few ways you can do it.
What You’ll Need to Sharpen Your Mower Blade – Equipment List
Here are the tools you’ll need to sharpen a lawn mower blade from start to finish. I’m guessing you already have most of them in your toolbox, so you’re off to a good start. You may be unsure of one or two items, but don’t worry, as I will explain these in more detail below.
- Protective Eyewear
- Heavy Duty Gloves
- Ratchet Set
- Blade Brace
- Sharpening Tools (metal file/angle grinder/bench grinder – only 1 necessary)
- Clamping Device (bench vise/C clamp)
- Balancing Device
- Angle Gauge (Protractor)
Prep You Need to do Before Sharpening a Mower Blade
It’s always a good idea to prepare before undertaking any kind of maintenance work, including sharpening a lawn mower blade. You want to ensure nothing will be damaged or hazardous, so clear away everything on your workbench and the area around the mower, as you will need to get under it to get to the blade(s). Now let’s take a closer look at the prep you need to do before you start sharpening your blade.
Working Out the Angle of the Blade
Before sharpening a lawn mower blade, you need to know the angle (INTERLINK) at which it should be sharpened. Angles can vary between blades and manufacturers, so you might need to research. If you don’t have any references to start your research, you can refer to your protractor and make an educated guess. In my experience, I have found that most lawn mower blades are sharpened to 30 degrees from the factory, apart from a few mulching blades that are sharpened down to 15 degrees. So if you use your protractor and have a reading somewhere close to 30 degrees, I’d be confident it started at 30 degrees.
Prevent the Mower from Starting
There’s more than one way that a mower can be started, so you need to make sure whichever of these are applicable in your case are deactivated before you go near the blade. I’ll run through the different systems that can start the lawn mower below.
If your mower has a string pull-start, you must locate the spark plug and disconnect it, then tuck the hood out of the way. You shouldn’t leave it swinging about because it may jump a charge and fire up the engine.
With an electric start, it’s a good idea to disconnect the battery and the spark plug; this will stop the starter motor from turning over and the plug jumping a spark.
If your lawn mower has an inertia starter, make sure you release the mechanical starter so that the coil/spring is released and the mechanism is fully discharged, then disconnect the spark plug.
Tilting Over the Mower
Believe it or not, there is a correct way to tilt over your lawn mower and a wrong way to tilt your lawn mower. You want to be tilting the mower over so that the oil doesn’t run into the carburetor or the air filter. The design of your engine will dictate which way you should tilt it.
If you happen to tilt it the wrong way, then you will be tipping oil into the carburetor, or you might be tipping oil into the air filter. If either of these situations occurs, you’ll have to remove the carb and the air filter and clean them. In the case of the filter, you’ll probably have to replace it.
Removing the Blade
With the mower dead and tilted over, it’s time to remove the lawn mower blade. There are a few ways you can go about this, but it all comes down to the same thing; releasing the center bolt without removing the skin from your knuckles.
I prefer a long-handled ratchet with the correct size socket and a pair of work gloves. Some guys like to get an impact driver on the bolts, but I find good old muscle works fine.
Brace the blade so that it’s unable to turn. For this, I brace the blade with a piece of 4×2 timber wedged in the deck that the blade pushes against. Now I have seen a neighbor use a pair of locking grips on the deck itself. It works, although I’m not too comfortable leaving marks on my mower deck, but that’s up to you.
With the blade braced, you can go ahead and use your tool of choice to remove the center bolt. Keep the brace at 90 degrees to the blade if you’re using a timber brace; this will stop the blade from riding over the wood and bending the blade. You don’t want to be dumping the blade straight in the trash because it’s bent, as I have done in the past.
You may find that no matter what tool you use or because of a lack of tool, you just can’t remove the center bolt, and you’re going to have to sharpen the blade without removing it. This is fine as long as the blade passes your blade inspection.
Inspect the Blade
With the blade in hand, you can perform your first visual inspection. There are a few different things you are looking for here to decide if you will move on to sharpening the lawn mower blade or if it’s going to be tossed in the trash.
The first element is to check if the blade is distorted. Over time the blade will inevitably strike objects that it wasn’t supposed to, like rocks, an old stump, or it may have chewed up a hose pipe or two. This would have put stress on the blade and potentially bent it out of shape.
Taking hold of the blade, look down it as if you were looking down the barrel of a gun. If the blade doesn’t look even and symmetrical, then unfortunately it is distorted. Depending on the severity of the bend, you might be able to use some elbow grease and get it straightened out.
Just imagine the distortion of a lawn mower blade to be like a buckled wheel on a bicycle; the more you ride the bike, the more it’s going to want to fall apart. In my experience, if you can’t get the blade perfectly straight, then it’s time for a new one. Your second visual inspection is to check the extent of the chips and dings.
Finally, look to see if you have any damage to the blade; minor defects to the blade edge are acceptable, as these will be removed during the sharpening process. If you find anything that appears too severe, then I’m afraid it’s going in the trash.
What You Want to Achieve
I’ve debated how sharp a mower blade should be many times; some will say as sharp as a razor, and others will say as sharp as a butter knife. I like to refer them to what a new blade looks like and ask whether they would sharpen a new blade. In my experience, I’ve never seen a razor-sharp new blade.
The points we can all agree on and what you want to achieve:
- Correct angle
- Flat sharpened edge
- No chips and dents
- No burr
- Balanced blade
How to Sharpen Lawn Mower Blades (My 3 Favorite Methods)
I know, right? There’s more to sharpening a lawn mower blade than you thought! Now that you have completed all the prep stages and have decided the blade is suitable to be sharpened and you know what you want to achieve, you can look at the different methods. Here you can determine what tools you already have and what you feel comfortable using.
Method 1: How to Sharpen a Lawn Mower Blade with a File
I will start with the simplest method I’ve used over the years. It’s a technique that never fails with results that have often surprised me with how easy and effective it is. So here are the steps you’ll need to sharpen a lawn mower blade with a file.
Place the Blade In a Vise
Take your blade and place it in your vise with the edge you intend to sharpen facing upwards and away from you.
Place the Blade on Your Work Surface Using a Clamp
If you don’t have a vise, you can alternatively use a clamp. Place the blade flat on the surface again, facing upwards and away from you.
Sharpening the Cutting Edge
Work the file using a long continuous downward motion starting from the blade’s center. Each pass of the file should extend the blade’s full length to ensure even metal removal. The angle of the stroke should match the angle of the intended sharpened blade edge; this is where you can check your angle with your protractor.
Continue the filing passes until you have achieved the sharpened angle and filed past any chips in the blade. Once complete, remove the blade, rotate it in the vise or clamp, and repeat the sharpening process for the opposite end.
Remove the Burr
During the sharpening, you will have inevitably created a burr on the back side of the blade. You now need to remove this using the same process as sharpening. This time, you do not want to create an edge. Instead, use the file flat to the blade, making the same continuous motion. This will slowly remove the burr on this side of the blade.
Balancing the Blade
Take your balancing tool and check if the blade is balanced. What’s a balancing tool, you ask? This tool will check if both sides of the blade match in weight. If you don’t have a tabletop balancer, you can use a nail on a vertical surface; I prefer to use a nail.
Place the blade on the balancer and check your results. If you discover one side is heavier, return to filing until you can balance the blade evenly. I like to do this bit by bit, so I make sure I don’t remove too much. If you over-file the heavy side, you’ll have to switch back to the other side, which gets tedious.
Method 2: How to Sharpen a Lawn Mower Blade with an Angle Grinder
Here I will describe the steps required to sharpen a lawn mower blade using an angle grinder. The only difference is that you will use a grinder and not a metal file this time. You can use the same clamping and balancing methods as before.
This is my preferred method as it takes a little less sweat, it can produce a better finish depending on your skill, and it can also file off the metal very quickly. Let’s look at how to sharpen a lawn mower blade with an angle grinder and the steps required.
Clamping Down the Blade
Without sounding like a broken record, use the same clamping methods as before, secure your blade and ensure that you have the lawn mower blade in the correct orientation.
Sharpening with an Angle Grinder
Using the angle grinder, take long continuous passes, starting from the blade’s center. Every pass of the angle grinder should extend the blade’s entire length, ensuring an even reduction of the metal. Keep the grinder in contact with the blade during each pass, applying light pressure so that minimal metal is removed.
You also need to ensure the grinder is in contact with the entire width of the blade edge during passes to avoid concave/convex sharpened edges. Check the angle being made with your protractor and adjust the passes accordingly.
Repeat the passes using this method until you are happy you have filed past any chips in the blade and achieved the required angle. Once complete, remove the blade, rotate it in the vice or clamp, and repeat the sharpening process on the opposite end.
Grind Off the Burr
Using the grinder on the backside of the blade, make a very light pass square to the surface to remove burrs. Repeat if necessary, being cautious not to create a second sharpened edge.
Check the Balancing
Balance the blade as previously described above, and return to the grinder if additional metal removal is required.
Method 3: How to Sharpen a Lawn Mower Blade with a Bench Grinder
My last method uses a bench grinder to sharpen a lawn mower blade. If, or should I say when, my angle grinder ever dies, this will be the method I adopt. In my opinion, this removes the guesswork and gives results close to what the factory can produce. So let’s delve in and see how to sharpen a lawn mower blade with a bench grinder.
Setting Up the Bench Grinder
First, start by disconnecting the power to the bench grinder so that it cannot function during setup. Now check the tool rest, ensuring it is secure and away from the abrasive wheel. During the sharpening, you will pass the blade horizontally (left to right or right to left) so that the edge to be sharpened passes over the abrasive wheel.
Next, place the blade on the tool rest, with the cutting edge being the highest part, so you can make passes like previously described.
Tilt the cutting edge towards the abrasive wheel, maintaining contact between the tool rest and the blade. When you have the blade in position, you will notice you have formed a triangle between the tool rest, abrasive wheel, and blade. By either pushing or pulling the bottom of the blade, you will adjust the angle at which the cutting edge comes into contact with the abrasive wheel, thus creating your sharpening angle.
Next, adjust the blade’s position to achieve the required sharpening angle. You will want to have your protractor at hand to ensure you achieve an accurate angle. Mark the tool rest where the blade sits using a piece of tape or a pen. Use this mark during the sharpening process to ensure that you repeat passes at the same angle.
Making Passes on the Bench Grinder
With the grinder set up, you can move on to passing the blade over the abrasive wheel. Firstly, you want to put on your protective gear and maybe have a fire extinguisher readily available to deal with unruly sparks.
Reconnect the grinder and power it up, lower the guards, and you’re ready to grind. Take your blade, starting with the center positioned at the wheel, following your mark on the tool rest. Slowly lower the blade onto the wheel to begin grinding and begin the horizontal pulling motion. Be sure to have a firm grip on the blade and only allow it to make light contact.
Keep repeating the pulling motion, resetting your starting position after each pass. If the blade has too much contact, it will probably grip the wheel; this will cause the blade to aggressively fly out of your hands and potentially cause serious harm, so take extra caution when sharpening. You’ll get the right feel after a few passes.
Before you get carried away and grind away the whole blade, inspect the blade between passes. Look how the chips disappear, and keep checking the angle with your protractor.
Removing Any Burr
Once you’re happy with your sharpening, you can flip the blade over and remove the burr. This time, you can take the blade and make a freehand pass without the tool rest; all you are looking to remove is the burr. Run the back side of the blade across the abrasive wheel at a reduced angle, getting as close to square as you can. I would imagine that you will only need to do one pass.
Balancing the Blade Evenly
Balance the blade, returning to the bench grinder as needed; make sure not to forget that if you grind the cutting angle, you will need to grind off the burr.
After You’ve Sharpened Your Mower Blade
You are now in possession of a perfectly sharpened blade, and you’re ready to reinstall it. But hold on, there are a few items you should address first.
The Perfect Time to Clean the Deck
Without a blade installed, it’s the perfect time to clean and inspect the deck. Take some time going around the inside with a scraper and really get into the corners. While you’re scraping, look for any holes or rust. This could be the ideal time to carry out rust repairs if necessary.
Listening to the Spindle
Having blades installed obstructs access to the blade spindle and it may be covering up hidden issues. Take a look and check that everything is in good shape. It would be a good idea to give the mechanism a spin if possible so you can listen for any unusual sounds. If you find anything, then this is the time to fix it. If all looks good, then give it a spray with a lubricant and tick it off the list.
Making it Easier for Next Time.
Before installing the blade, think back to how it was when you removed it. Spraying a lubricant into where the bolt goes and onto the bolt will ensure it’s an easy task next time. You don’t want to end up with a seized bolt.
Installing the Blade the Right Way
As silly as it sounds, it’s too easy to install a mower blade upside down. Blades are designed to lift the grass and allow the blade to cut at a uniform length. After all your effort sharpening your blade, it would be a shame to put it on backward, not that you would be the first. So remember the cutting edge is up, and don’t forget any metal washer spacer that goes with the blade.
My Top Tips to Increase Your Chances of a Successful Sharpening
Finally, here’re my top tips to help improve your chance of successfully sharpening your lawn mower blades based on my experiences over the years.
- Always use protective gloves and eyewear.
- Have a long fie of at least 12-inches
- Sharpen from the top side of the cutting edge
- Use your file/grinder in one direction.
- Know the correct angle to sharpen the blade.
- Use a metal flapping disc on your angle grinder.
- Avoid gimmicky sharpening tools.
- Have a spare lawn mower blade.
- Take your time.