How to Sharpen a Lawnmower Mulch Blade

The performance of a lawn mower is not solely dependent on its specific components such as engine power or cutting deck. The sharpness of the lawn mower blades plays a significant factor when it comes to creating a manicured and clean-cut lawn.

Dull cutting blades cause ragged tears on the grass blades as these cutting blades rip and pull them off instead of cutting it smoothly. Sharpened blades do not only cut cleanly, but it also helps the plants heal and recover quickly. Lawn mower blades with dull edges do only result to a poorly mowed lawn but can also extend the lawn mowing time. It is recommended that the cutting blades of the lawn mower should be sharpened at least twice every season in order to keep a healthy lawn.

Now, this might be a tedious job for some as it requires some specific steps to be followed. However, once acquainted with the process, sharpening lawn mower blades should not be a chore as it would come naturally.  Here are some of the things needed to sharpen lawnmower mulch blades and the steps on how to do it

Items required for sharpening lawn mower blades :

  • ​An approved gasoline container for handling and use of flammable liquids
  • ​A block of wood, preferably 2-by-4 inches
  • ​Spray paint
  • ​Socket wrench
  • ​Rubberized gloves
  • ​Vise Grip
  • ​Files

​​Steps On How To Sharpen Lawn Mower Blades

  • ​Ensure that the spark plug wire is removed from the lawn mower assembly. Spark plugs are usually installed in front of or near the engine. If this is left plugged while sharpening lawn mower blades, it can trigger accidental starting and can be a hazard to the one working on it. Do not use tools to unplug the spark plug as it could damage the plug wire. It is advisable and completely safe to remove it by hand.
  • ​Drain the gasoline from the lawnmower. This is to ensure that accidental starting would not be possible because the mower has no gas to power and run from. Place the gasoline from the mower's tank into an approved gasoline container. It is necessary to use gasoline containers that are approved by the Department of Transportation to ensure that there is no leakage or unnecessary spills during the transferring and transporting process. Some lawn mowers have their own gasoline drains. But for some, filling of the approved gasoline containers can be started by unscrewing the valve of the lawn mower's gasoline tank. If, however, the mower tank is not equipped with a drain, the mower has to be tipped off to its side to drain the tank.
  • ​Once the gasoline has been drained off, tip the mower to its side to access its cutting blade.
  • ​Place a wooden block beneath the blade and the mowing deck to stop the blade from turning when it is being loosened from the mower assembly.
  • ​Spray a little but visible amount of paint on one of the blade's surfaces to help identify the top and bottom part of the blade when it is reinstalled after sharpening.
  • ​Loosen the nut that holds the blade in place. In this part, the use of tools such as a socket and driver are recommended due to the deep size of the nut. This shall give a leverage clearance that is just enough to loosen extremely tight bolts and could keep knuckles away from the blade when working. For rusted and stuck bolts, a small amount of penetrating oil can be sprayed over the surface of the bolts. Leave the bolts with the oil for about 10 minutes before loosening it once again.
  • ​Remove the blade. Place it in a vise grip to make it steady as the blade is sharpened. Make sure that the beveled cutting edges are faced upward as the vice on the center portion of the blade is secured.
  • ​Upon removal, the blade should be examined if it can still be sharpened or it its edges are either rusty or dull enough to be replaced.
  • ​Hold the file at the same angle as the beveled edge. While doing so, push the file toward the edge of the blade to sharpen it. File the edges until the straight portion of the cutting edge is straight. Mower blades are usually made from soft steel; hence, making a hand file a good choice to sharpen it properly. To achieve a "butter knife" blade, its edges should have received more or less 50 strokes from a clean and sharp mill bastard file that is at least 10 inches long. Grinders also usually work quicker than these files. However, these are more difficult to control and might overheat during the process, causing the cutting blade to be ruined.
  • ​Always sharpen from the top side of the cutting edge. During this time, knowing which is the top and bottom should be easy due to the paint markings. This side of the cutting edge shall give the longest-lasting edge on the blade.
  • ​The file should cut in one direction only. If the file is pressed down against the blade properly, it should be locked in place. This means that the file was adequately biting into the steel on the blade. If there is no cutting action, then the file is probably dull, or it is not pressed down hard enough to the blade. Do not make the blade razor sharp as it could dull more quickly.
  • ​As the curved portions of the cutting blade are reached, change the file to a narrower one to cater those hard to reach edges. Narrower files also allow sharpening the edges easily than wider files. Some mulching blades can be tougher to sharpen because of the mulching blades longer or curved edges. Several types of files may be needed to sharpen these blades. In some cases, a 4.5-inch angle grinder is used to sharpen mulching blades.
  • ​Repeat the filing process until the edge of the cutting blade is sharp enough. Afterward, switch to the other side of the cutting edge and file it in the same manner until the desired sharpness is achieved.
  • To check if the sharpened edges are balanced, hang the blade from a nail. Insert the nail through the hole that is bored into the center of the blade. If both the sharpened cutting edges are equal, then the blade should hang evenly. However, if one edge tilts more to the side, hang down the blade and repeat the filing process focusing on the side that hangs lower this time around. After filing once again, check the blade for sharpened balance by hanging the blade from a nail again. Do this until desired balance is attained.
  • ​Reinstall the cutting blade back on the shaft of the cutting deck. Be sure that the nuts of the blade are tightened. The nuts of the cutting blade can be tightened by hand to ensure that it is secured tightly. A 2x4-inches wooden block can be inserted in the reverse direction to help the user bear down on the bar to tighten the bolt. Check if the bolts are tightened properly and do not be afraid to over-tighten the bolts as these require a lot of force. It is better to over-tighten it than to have a loose bolt as this can throw off the engine timing and can sometimes make the mower hard to start.


​When sharpening the blades, always put safety first. Make sure to wear rubberized gloves at all times to avoid lacerations and further injuries. These are just some of the general steps in sharpening lawn mower blades. Some cutting blades require different added steps and precautions as these blades have different edge designs.

The tools needed and the procedure can be altered depending on your preference. Some mulching blades need an added force when a simple nail file is used for the sharpening process, so this may not be convenient enough for you to use.  Instead, opt to choose other files which will make sharpening easier. When selecting the right tools to sharpen lawn mower blades, it is essential that you should choose the ones that could get the job done efficiently and safely. Again, these steps may be hard to follow at first, but once you are familiar with the process, it should come off easy for your next sharpening sessions.

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