Forget The Metal File: There's A Better Way To Sharpen Zero-Turn Lawn Mower Blades

Sharpening one mower blade with a metal file is manageable, but sharpening several blades is a much bigger job. Many sit-on mowers have wide decks containing one, two, or three blades, leaving a number of cutting edges to restore. For that amount of work, an angle grinder fitted with a grinding wheel is usually faster and easier than using a metal file. 

While metal files can be used to safely sharpen the mower blades, these tools take more time and physical strength. A normal grinding wheel cuts off the worn-off metal faster than the sanding wheel does. That's why it is better to use a grinding wheel when your blades have dull or rounded edges or a nick. A flap disc is another way to go. It cuts the metal at a much slower pace, leaving it smoother. The use of this type of attachment allows you to get a smoother blade after sharpening; however, you may need to spend more time on the process. In order to save your time and effort, it's best to use the grinding wheel first, then the flap disc.

Regardless of the type of attachment, you must sharpen the blades following their current bevel. You should not try to grind the new angle or make the blade razor-thin. A thinner blade will be weak and may become dull very fast.

Start off by reading the instruction manual, as the process of accessing the blade differs from one mower to another. Some will have an in-built lift system, whereas others will need the deck or the whole mower to be lifted using proper tools. Park the mower on level ground and set the brake. Disable the blades, switch off the engine, take out the key, and ensure that all moving parts stop working. Disconnect the spark plug wires before going under the deck. You should take a picture of each blade and all of its fastening hardware prior to removing it. The picture will serve as a guide for proper orientation of the blade and fasteners. 

Each blade should be thoroughly cleaned and inspected. Cleaning the deck and sharpening its blades are both important parts of routine lawn mower maintenance. Clamp the first blade securely to a solid work surface. Keep the grinder's safety guard attached, and wear eye, face, and hearing protection. Place the grinding wheel against the beveled side of the cutting edge. Move it along the existing angle using short, controlled passes. Pause periodically to prevent the blade from becoming excessively hot.

Be sure to cut back an equal amount of material on both sides of each blade. If they aren't balanced, then cut away a little bit of metal on the heavy side and rebalance the blade. Do this with each and every blade. Then remount the blades in the configuration as shown in your manual and tighten the hardware to the required torque value. If you cannot safely reach the deck or control the grinder, professional sharpening is the easier option.