How to Sharpen Lawn Mower Blades – The Best Ways and Tips

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Keeping your lawn mower blades sharp can help to keep your grass healthy. Dull blades can damage the grass, making it more susceptible to disease and fungal growth.

Grass cut with a sharp blade, on the other hand, stays healthier. As a result, sharp blades can literally support green, thriving grass. In addition, sharp blades reduce cutting time so you can finish your lawn mowing chore more quickly. 

How to Sharpen Lawn Mower Blades

Many mower owners, however, do not realize that they should sharpen their lawn mower blades twice a year. Nor do they know how to go about it. This guide will help you learn both the steps and the tricks for successfully sharpening your lawn mower blades.

Step 1: Don protective gear

Sharpening lawn mower blades is a relatively simple process. It does, however, require the use of some protective gear to shield you from sparks, metal shavings, noise, and moving parts. Don the following gear before sharpening your lawn mower blades:

  • Safety goggles
  • Work gloves
  • Ear plugs
  • Long sleeves

Step 2: Disconnect power sources

Since you are working with the sharpest and most dangerous part of your lawn mower, you don’t want it accidentally turning on. To prevent this potentially serious accident, disconnect any power source to your mower.

In the case of electric mowers, unplug the cord or remove the battery pack. In the case of gas-powered mowers disconnect the spark plug before attempting to remove the lawn mower blades. You can easily disconnect the spark plug by removing the ignition wire from the plug. 

Tip 1: Tape the ignition wire back so it cannot move into contact with the spark plug while you are working.

Step 3: Remove the blades

Before you can sharpen your lawn mower blades, you must remove them from the mower

To remove the blades from the mower, you must first tip the mower over. This move may damage the mower if you are not careful. Check your instruction manual for directions on how to safely tip your lawn mower in order to gain access to the blades. You can also prevent damage to your mower by making sure that the air filter and the carburator are both facing up once the mower is on its side. 

Tip 2: In order to prevent fuel spills, drain the gas from your mower before placing it on its side.

Remove to sharpen lawn mower blades

Once the mower is tipped over, use a wrench to loosen the bolt that secures the blade to the mower. Use a long-handled wrench, or a metal bar placed through the handle of the wrench to give you the leverage you need to loosen the bolt. 

Tip 3: To prevent the blade from moving, and potentially cutting you while you remove it, place a wooden wedge between the blade and the cutting deck. Make sure the wedge is at a 90-degree angle and avoid putting pressure on the blade because that pressure might damage the blade. 

One important part of this process is marking which end of the blade faces down when you remove it. Adding a little bit of spray paint to the blade can help you remember. The blade must be replaced in the correct position when you finish sharpening it, so marking the correct orientation now can save you time and frustration at the end of the process of sharpening your lawn mower blades. 

Tip 4: If the bolt is rusty, apply a few drops of penetrating oil and wait 10 minutes before trying to remove the bolt again. 

Step 4: Clean the lawn mower blades

Once you remove the lawn mower blades, you will need to clean both them and the cutting deck. First, knock out any clumps of dirt or grass you see in the cutting deck. These clumps often get stuck between the blades and the cutting deck while you mow. Removing them will preserve your mower and make mowing easier the next time around. 

Next, use a putty knife to scrape away any debris that remains stuck to the inside of the cutting deck. Apply penetrating oil to the underside of the deck and wipe it until it is clean. A stiff bristle brush can help you remove particularly stubborn spots. Then, place the lawn mower back in its upright position. 

Next, take a rag and gently wipe down the blades. Once the cutting deck and blades are clean, you can begin the process of sharpening your lawn mower blades. 

Step 5: Sharpen the lawn mower blades

Once the first four preparatory steps are completed, you can begin the process of sharpening your lawn mower blades. You have two choices when it comes to which tool you use to complete the sharpening process:

  • Sharpening by hand using a file or chisel
  • Sharpening with a bench grinder

Tip 5: When sharpening with a hand tool, always use a clamp to conveniently hold the blade at a 45-degree angle while you work. 

Sharpen the lawn mower blades

Regardless of which tool you use, the basic process is the same. You use your tool of choice to smooth out and sharpen your blade until you no longer see or feel bumps or roughness in the blade. There are a couple of things to keep in mind as you sharpen

  • Follow the angle of the blade edge

You want your blade edge to go in the same direction as it does when you remove it from the lawn mower. As a result, whether you are using a hand tool or a bench grinder, make sure to follow that edge and bring it to the sharp point you want for cutting your grass. 

  • Sharpen from the top side of the blade

You want your sharpening job to last as long as possible. As a result, sharpen along the top side of the blade for a result that will last longer. 

  • Sharpen until the edge is butter knife sharp

Your instinct may be to sharpen until the blade is razor sharp. However, a butter knife sharpness is sufficient to keep your grass happy and healthy, and the edge will last longer that way. 

Step 6: Balance your blade

Once you feel that your lawn mower blade is sharp enough, you should check its balance. If one edge is sharper than the other, the blade will not balance, and you will need to sharpen the other end more to make it even. 

You should make sure your blades are balanced because unbalanced blades can cause wobbling while you mow. This wobbling can damage your lawn mower, not to mention create an unpleasant mowing experience. 

Checking the balance of your blades is a relatively simple process. You can use a nail on a wall, a rod, or any other long, narrow tool that slips through the hole in the center of the blade. Watch the blade or spin it. If the blade tips, then it is not balanced. Sharpen the unbalanced end until the blade does balance correctly. If the blade does not tip, it is already balanced, and your sharpening job is complete. 

Tip 6: For more accurate results, use a lawn mower blade balancer to see whether your blades are balanced. 

Step 7: Reinstall the lawn mower blade

Once your blades are sharpened and balanced, you can go ahead and reinstall them. The process of placing them back on your mower is the following: 

  1. Tip your lawn mower back on its side, following the same precautions as before. 
  2. Note the correct orientation of your blades.  
  3. Position the blades correctly, with the spray painted ends facing down.
  4. Place the bolt in the correct position and use the wrench to tighten the bolt. 
  5. Reattach the ignition wire to the spark plug, or put the battery pack back in. 
  6. Stand the mower up.

Tip 7: Once the blade is reattached, take the mower for a test run. Check for proper cutting of the grass, and a smooth operation of the mower.

A mower with sharp blades cuts your grass without damaging it. Make sure to sharpen the blades twice a year, or whenever your cut grass begins to show a ragged edge. Regular sharpening will keep your mower in top working condition and your grass as healthy as possible.  

To get a visual look at how to sharpen lawn mower blades, check out this video:

Rose Hawes

Rose Hawes

A former master gardener, I hold a Bachelor of Arts degree in creative writing and have been published in magazines such as Woman's World, Birds and Blooms, and Writer's Digest. I've also created hundreds of gardening articles for online sites such as Dave's Garden, eHow, and SFGate.

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