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Sharpen a Rotary Mower Blade
Level of difficulty: Beginner

Don't beat your grass into submission with a club. A dull blade doesn't cut evenly, strains the mower, increases the chance of lawn disease, and turns the tops of the grass brown. Damage and wear can also throw the blade out of balance, resulting in excessive vibration that is both uncomfortable for you and harmful to the mower. The blade doesn't need to be knife-sharp, but you need to maintain the cutting angle and remove nicks. This requires sharpening the blade once or twice a season and as needed to repair damage from stones.

To get the mower ready for a new season or tuned up for better fall mulching, you should remove the blade and lock it in a vice for sharpening and balancing, as shown below.

Before You Begin:
Drain the fuel from the mower into a clean container using a siphon hose, which is a handy and inexpensive gadget available from hardware and outdoor power equipment dealers. If you're careful about spills, you can tilt the mower to drain fuel into a bucket. Inspect the blade carefully. If the blade is dull, but in good condition, you can sharpen it. However, you should replace a blade if (1) the cutting edges have been severely damaged or are worn to the point that the cutting angle is no longer obvious; (2) the blades are twisted; or (3) the lift wing (the upward bending part of the blade opposite the cutting edge) is badly damaged. Never try to suck gas into a hose to start a siphon. To filter out any residue, secure a clean cloth over a second clean container with a rubber band and pour the fuel through it.

Tools and Materials:

Siphon hose and clean container
Heavy work gloves and goggles
Stiff putty knife
Lumber scrap
Socket wrench set
Bench vise or C clamps
Rotary blade sharpener accessory
Electric drill
Double-cut (medium-rough) flat file
Screwdriver, or 1/4-in. rod or bolt
Blade balancer
Replacement blade

1. Disconnect Spark Plug

		Whenever you work on a mower, unplug the spark plug wire and tie it to one side to keep it from contacting the plug. No spark, no start. It's so easy, so why take a chance?


	Tip:

		Avoid skinned knuckles: Wear heavy leather work gloves during the entire project.

2. Clean Deck and Remove Blade

		Scrape off any grass buildup from the underside of the mower deck. If you plan to take the blade off for a full sharpening, remove the blade first. To remove the blade, place a 2x4 between the blade and the mower deck to wedge it in place, then use a socket wrench, turning counterclockwise, to remove the bolt(s).


	Tip:

		If the bolts are stubborn, give the wrench a sharp blow with a rubber mallet.

3. Sharpen with a File

		Secure the blade in a bench vise or to a worktable with C clamps. Holding a double-cut flat file by the handle with one hand and applying pressure on the other end with the flat of your palm, use slow, controlled strokes to sharpen the blade, following the original cutting angle. Wear goggles to protect your eyes!

4. Sharpen with Accessory

		Grind off nicks and burrs from the flat side of the blade. Set the tool on the blade with the nylon guide against the flat side. Turn the drill on, apply light pressure, and move slowly along the cutting edge. Be sure to sharpen only the last few inches, not the entire blade. Repeat for the other cutting end. Wear goggles to protect your eyes.


	Tip:

		Be careful as you near the end of the blade because the sharpener might jam.

5. Sharpen in Place

		In a pinch or for touch-up sharpening, a handy rotary mower blade sharpener drill accessory allows you to sharpen the blade on the mower. Be sure to wedge a block of wood between the blade and the mower deck to hold it securely in place. That will free both hands to guide the drill and the sharpening accessory.

6. Balance the Blade

		Insert the blade of a screwdriver or other tool, or a 1/4-in.-diameter rod or bolt into the center hole to check the balance. If the blade rotates to one side, file or grind off material from that end of the blade. Repeat this procedure until the blade balances. (An inexpensive cone-shaped blade balancer will be more accurate than the screwdriver/rod method.) Reinstall the blade, then tighten the mounting bolts and any lock washers securely.


	Tip:

		If the blade is secured with more than one bolt, twist each bolt until it is just snug; then go back a second time to lock each one down tight.