We can’t count the number of times we’ve been asked by neighbors or colleagues about the best way or how to sharpen a lawn mower blade. Sharpening a lawnmower blade doesn’t require a ton of skill. While years of practice make you better, anyone can learn the basic principles needed to complete the job using any of several tools. We set up this handy lawn mower sharpening guide to work with several different methods. Check out our introduction and then look over the tools you might have on hand to get that lawnmower blade sharpening job done.
Why Sharpening Your Lawn Mower Blades Makes a Difference
I’ve known friends who have never sharpened their lawn mower blade…ever. Apparently, if the mower does something to chew the grass down to 2.5-inches or so, that’s all they require. And it may be natural to think that a blade spinning at just under 200 mph wouldn’t need to be terribly sharp in order to cut grass. You’d be right. However, a sharp lawn mower blade slices through the grass. With a clean cut, your grass stays green and you avoid that unhealthy brown or burnt look that plagues so many lawns—even when they get plenty of water.
Check out the photo below and see if you might start to get the picture:
For professionals and people who want their lawns nice, healthy, and as green as possible, knowing how to sharpen a lawn mower blade makes the difference. This goes double for grasses like Fescue which tend to grow very straight and require frequent cutting.
In the professional landscaping world, some professionals sharpen their zero-turn lawn mower blades every other day. When your business is nice-looking lawns, you need to do everything in your power to ensure you keep them healthy.
How to Sharpen a Lawn Mower Blade With an Angle Grinder
As we mentioned earlier, you can sharpen a lawnmower blade using any number of tools. One of the easiest (and quickest) involves using an angle grinder. Of the people I’m aware of who already know how to sharpen a lawn mower blade, most use an angle grinder. The reason this works is that lawn mower blades don’t need to be razor-sharp. They do, however, need a clean cutting edge—preferably at the proper angle. This clean edge lets the blade slice, instead of chop, through the grass at high speed. It’s the difference between cutting carrots with a knife and a piece of 1/8-inch steel swung wildly through the air
Step 1: Position the Mower on Its Side
The first step may seem obvious but we’ve been around for a while…and we’ve seen some crazy stuff. In case it isn’t already clear, don’t sharpen the blade on the mower. For one, it doesn’t give you enough room to maneuver the grinder. Second—the majority of the work needs to take place on the top side of the blade. Third, it’s dangerous since there’s no good way to keep the blade from spinning around on you.
To remove a lawnmower blade, first, get the mower into a safe position. For a gas mower, remove the spark plug wire to ensure the motor cannot fire. Then turn the mower onto its side (carburetor/air filter side facing upwards) to expose the blade. Turning it this way helps keep the engine from flooding and oil from leaking.
Step 2: Remove the Blade from the Lawn Mower
Use a 1/2-inch impact wrench if you have one. While this may have been an obscure tool for a consumer to have just a few years ago, manufacturers are bringing cordless impact wrenches more and more into the mainstream. So grab a grinder if you have one. If you don’t, use the longest ratchet you have with the appropriate socket. If it’s still not budging, use a piece of 2×4 or similar material and tap the ratchet handle with a hammer via the wood (so you don’t damage the tool). Be careful as the ratchet can easily slip off the center bolt.
Step 3: Secure the Blade in a Vise and Sharpen
Secure the blade in a vise with the sharp portion of the blade positioned accessibly towards you. Using a small angle grinder, sharpen the lawn mower blades using a smooth, steady motion along the length of the sharpened portion of the steel. You want to match the existing angle of the blade, not create your own angle. This ensures the blade continues to maintain its proper lift and functionality.
Remember, the goal of lawnmower blade sharpening…is to sharpen the blade, not recut a new edge from a block of flat steel. Work with the metal! Try to remove the same amount of metal from each side of the blade so you maintain the balance of the blade. See our section below on balancing the lawn mower blade before you finish.
How to Sharpen a Lawn Mower Blade With a Bench Grinder
Knowing how to use a bench grinder to sharpen lawn mower blades helps you in a number of ways. For one, a bench grinder makes it easier to maintain the sharpening angle on the blade. You no longer need to rely on your hands to steady the grinder. Instead, a bench grinder gives you a place to rest the blade against and set up your angle. Let’s assume you already followed the steps above to remove the blade from the mower.
Step 1: Set Your Table Angle to Match the Existing Blade Angle
A bench grinder reverses the process of sharpening. Rather than move the grinder across the blade, you move the blade back and forth across the grinder wheel. Most bench grinders feature a table that tilts. Using this you can really get consistent results using this method. Set the angle of the table before you turn on the grinder and begin sharpening.
Step 2: Start the Bench Grinder and Slide the Blade across the Table
Be sure not to over-sharpen the lawn mower blade when using a bench grinder. You only have so much steel to work with before you have to get a new blade. You also don’t need to do much more than put that edge back on. Use quick passes back and forth when sharpening. This helps keep you from heating up the steel and eliminating the hardening process. This helps you keep that blade edge sharp for longer periods of time.
How to Balance a Lawn Mower Blade
Regardless of how you sharpen a lawn mower blade, you want to finish by balancing the blade. When you remove metal from each side of the blade, you affect the blade’s balance. Just like your car—which needs all four wheels properly balanced—lawnmower blades must also be balanced. If not, it can cause excessive vibration and reduce cutting efficiency.
Step 1: Create a Balance Point
Hammer a 16D or similar nail into a stud in your shed or shop and hang the blade from its center point. In theory, you could simply hold out a nail and do this step by hand if needed. Some blades are harder than others to balance due to the nature of the center hole. The easiest to balance use round holes.
Step 2: Mark the Heavy Side
If it stays balanced, you’re all done. If not, mark the blade on the heavy side with a Sharpie marker. I typically mark the actual sharpened edge so I have something to remove.
Step 3: Continue Sharpening and Re-measure
Next, grind away some more metal off that side. Be sure to maintain the same cutting angle. Just do a little bit and then re-check your blade balance.
Regardless of which grinder method you use, balance the blade each time you sharpen it before mounting it back on the lawn mower.
Other Tools and Methods to Sharpen Lawnmower Blades
Save yourself a lot of headaches and don’t use a file to sharpen lawn mower blades. You don’t need to have that level of accuracy, and it’s just slower and more work than you need for this process. Regardless of what anyone says, you won’t get a nicer-looking lawn or longer blade life from manually sharpening the blade with a file. Use one of the grinding methods above and git ‘er done!
For commercial users who do a lot of lawn mower blade sharpening, several companies make tools that can help speed up the process…potentially. We tried a tool from Noracore called the Easy Mower Blade Sharpener (EMBSX). It uses a die grinder, mirrors, and a camera connected to your smartphone to let you sharpen blades on a zero-turn mower without removing them. While it has some potential, it also had difficulty getting to that center blade on 3-blade ZTs. It’s clearly an innovative tool. In fact, it won a 2019 Pro Tool Innovation Award . In the end, you’ll need to determine whether it might be easier just to jack up the mower and pull the blades.
Other systems include jigs for quickly setting and maintaining angles on even complex mower blades. These help you maintain that proper edge—which can vary between 30 and 45-degrees depending on the blade. If you do a lot of sharpening, find a system that optimizes your time to save you the most money.
Some More Considerations
Regardless of how you choose to sharpen a lawn mower blade, be sure you wear proper personal protective equipment (PPE). Protect your eyes, hands, and ears whenever working with grinders. Grinding mower blades takes very little effort. It’s a great entry-level task that almost anyone can tackle.
Let us know what you think in the comments below. Do you have a preferred method for sharpening lawn mower blades? Which method works most consistently in your experience? We’d love to hear from you.