How to Sharpen Lawn Mower Blades

It’s a good idea to sharpen lawn mower blades every four to six weeks.

Your lawn will tell you when it needs to be sharpened. Dull mower blades tear, shred and bruise grass leaves. The frayed leaves will turn brown and then white, making your lawn look ugly. Sharp blades cut cleanly, leaving your lawn looking manicured.

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Sharpen lawn mower blades

Tools You'll Need

  1. 12″ Mill File, Bench Grinder or Angle Grinder
  2. Bench Vise
  3. Block of wood and C-clamp or a Blade Holder
  4. Wrench to remove the blade
  5. Blade Balancer
  6. Spare Blades (optional)

Tip: Keep a sharp, spare blade on hand. Then you will have the option to swap the sharp blade with the dull one – And then sharpen the spare at your convenience. A spare lawn mower blade will cost you about $15.

Sharpening Lawn Mower Blades

Bad example! Don’t use your hand to hold the blade like I’m doing. Use a Blade Holder or a 2×4 clamped to the deck to hold the blade.

How to sharpen a lawnmower blade

Clamp your blade in a vise.

How to sharpen a lawn mower blade with a file

The best way to sharpen lawn mower blades? Use a flat file. Grinders take off too much material and will weaken the metal if you are not careful. Be sure to follow the factory bevel.

How to sharpen a lawn mower blade

Sharpened lawn mower blade

How to sharpen a lawn mower blade

Use a blade balancer to check the balance.

How to sharpen a lawn mower blade with a drill sharpener

I picked up this blade sharpener that attaches to a drill at Home Depot for about $7. You can find similar ones on Amazon. It works pretty well. However, it’s easier to keep the correct angle using a flat file.

Sharpening Lawn Mower Blades

Remove the blade

Work safely and keep all your fingers – disconnect the spark plug wire to make sure the engine does not accidentally start. When tilting your mower on its side, make sure the side with the air filter is on top. This will keep oil from draining into the carburetor and saturating the air filter. Spray some WD40 on the blade bolt and give the penetrating oil a few minutes to work its way into the threads. Then mark the bottom of the blade with a Sharpie to help you reinstall it properly. Inspect the blade after you remove it. Cracked or bent blades need to be replaced. Cleaning grass buildup around the center bolt hole of the blade will guarantee a tight fit when you remount the blade.

Sharpen your blade with a grinder or file

OREGON makes a nice lawn mower blade sharpener – Lawn Mower Blade Grinder Pro Series (See all Mower Blades & Sharpeners) it costs about $700. There is a drill bit grinder that sells for $7 at Northern Tool, Home Depot,, and other hardware stores. You can pick up a mill file for $5 and they work as well or better than a grinder. Clamp into a viceSharpen with a bench grinder, hand-held grinder or flat file. Be sure to follow the factory bevel. It is quicker to use a grinder if your blade is really dull and full of nicks. However, you don’t have to grind all the nicks out – just get a sharp edge. Be careful if you choose to use a grinder, they tend to remove too much material quickly and will overheat the metal – weakening the mower blade. Keep a bucket of water on hand and cool the blade by dipping it in water frequently. If you sharpen your lawn mower blades every couple of weeks, simply run a metal file along the cutting edge – file toward the sharp edge of the blade while maintaining the correct angle. Remember, files remove metal on the push (or forward) stroke – lift after each stroke. Use the file on the flat side to knock off any burs left by sharpening. When sharpening, try to take an equal amount of metal from both ends of the blade to keep it in balance.

Balance the blade

Your mower will run smoother. An out-of-balance blade will cause severe vibration that will damage your mower engine. Use a blade balancer (most hardware stores carry them) to check the balance. File metal off of the heavy end to reduce weight.

Re-install the blade

Remember you now have a very sharp blade, install it carefully. If you marked the bottom of the blade you should have no problem installing correctly.

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