Nicked and dull lawn mower blades make an already dreaded task even hard to accomplish. Instead of slicing through the grass, a dull blade rips the grass. This slows down the engine, leaves more uncut grass in the yard (which looks cut but pops back up in a few hours), and makes you work twice as hard. Don’t let a dull blade keep you down, grab your grinder and we’ll show you how to sharpen a lawn mower blade!
Removing the blade is fairly easy. First, remove the spark plug from the engine to prevent accidental ignition. Then lay the mower on it’s side and unbolt the blade using the wrench. You may need to use a 2×4 to stop the blade from turning. Mark the top or bottom of the blade so that you know which side is up. If you install the blade upside down, it won’t do much good.
Unlike sharpening a kitchen knife, there is no specific angle that you need on your lawn mower blade, just as long as it is smooth and sharp. There are two methods to getting this done- hand file or power grinder. Flat blades have short cutting edges and are not curved. These can easily be sharpened with a file. If you have big nicks in the blade, then you will probably want to move on to the power method, as it can take some time to work a nick out of the blade by hand. The grinder method uses a hand-held 90-degree grinder with a grinding wheel or flap disc mounted. I prefer a flap wheel as it cuts quickly without gouging the metal or leaving a rough finish. The more smooth the edge is, the better it will cut.
Locate any nicks in the blade. You will want to mark these so you can find them as you go. If the blade it heavily nicked, you might need to flatten the edge first to remove the nicks and get a good surface to sharpen.
Pro Tip- Wear safety goggles to protect your eyes. Safety first.
Work the grinder over the edge at roughly a 45-degree angle. This will leave plenty of meat to back up the edge so it does not dull as fast. You only need a “butter knife”-like sharpness, anything more will dull quickly.
Putting It Back Together
Once the blade is sharp, you can check the balance of it by hanging it on a nail in the wall. The blade should lay out flat and not swing one side down. If one side is heavier, the imbalance will throw off the engine and the mower will shake. You can always balance the blade by grinding a little material off the heavy side. Be sure to check you blade for bends. A warped blade will make the mower shake and not cut very well. When the blade gets thin or bent, it is time for a replacement. Only use the correct blade for your mower, they are not universal.
Stay safe and happy mowing!
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A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.