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How to Sharpen Lawn Mower Blades

Getting Your Lawn Mower Blades for Summer

Summer is the season of lawn maintenance, and everyone likes to look outside and see a pristine green carpet.  Mowing your lawn is the first step in having a manicured yard, and having a well-sharpened blade is the most important component of any lawnmower.  As they pass over the grass, if the blades are too dull, they will not cut the grass cleanly, but rather they will tear them off at the end, leaving messy, frayed openings that are openings for fungi to creep in.  A sharp cutting edge not only makes your cuts look more even, it will also cleanly shear the ends off each blade of grass, which prevents diseases from getting in and causing discolored brown patches in your yard.  Don’t be intimidated: sharpening a mower blade is a very quick and easy activity.

Tools You’ll Need:

  • Wrench
    • A ratcheting socket wrench is ideal, but adjustable wrenches also work just fine
  • Bench grinder
  • Wood block
  • Common nail & hammer

Step-By-Step Guide for Sharpening Lawn Mower Blades:

1. Disconnect the Spark Plug

Disconnecting the spark plug is the first step you need to take to sharpen your lawnmower’s blade.  This is a safety measure to prevent the motor from accidentally turning on while you are working on it.  There is always a chance that there is compressed gas in the cylinder, and one accidental spark could send the blade spinning with enough force to chop a finger off.  It’s a gruesome image, and it’s not a risk worth taking.

With electric mowers, be sure that the power cord is unplugged or the batteries are removed.  This will serve the same purpose as disconnecting the spark plug from a gas motor, and protect you from the motor energizing with your hands in the path of the blade.

2. Tip the Mower To Reveal the Blade

The blade attaches to the bottom of the mower, so you will need to tip it up to have access to it.  Be careful as you do this though; if you have a gas-powered model, be sure to keep the carburetor pointing upwards as you tip it over.  If you don’t, gas and oil could spill out, which will kill your grass and cause a toxic environment.

3. Mark the Bottom of the Blade

Once you are finished, it can be difficult to remember which side of the blade needs to be facing up or down.  Mark the bottom of the blade with some tape or a marker, and it will be much easier to reattach the right way.

4. Secure The Blade

You will need to secure the blade so that it doesn’t spin while you loosen the bolts.  One simple method is to simply wear a sturdy pair of work gloves and firmly grasp it with one hand.  You will want to wear gloves to protect your hand from any jagged edges that could exist.  

Another popular method is to jam a piece of wood under the blade so that it wedges. This can be any block, whether it is firewood, a 2×4, a wooden dowel, or any other, so long as it is tight and will not break under mild pressure.  

5. Remove the Blade

There are typically between 1-3 nuts holding the blade in place, as well as washers or other layers to offer a more secure hold.  A ratcheting socket wrench works great for this step, and so does an impact wrench if you have one. You will need to check your individual model for specifications about what size the nuts are. Some nuts are also self-tightening as the blade spins, so you might need to apply a good amount of force to break them loose.

6. Clean the Blade

The blade will likely be caked in grass clippings from use, which you will want to clean off before trying to sharpen it.  A good way to do this is by spraying it with a hose, then scrubbing it down with a soft brush. Cleaning out the underside of the lawnmower deck this way is also a good idea while the blade is detached.  This will also preserve the life of the mower and make it run more efficiently.

7. Make Sure You Have the Proper PPE

Before you begin sharpening your blade, be certain you have the proper personal protective equipment.  Safety glasses are absolutely necessary because the grinder will throw a large number of sparks. Long sleeves with tight cuffs are optional to protect your arms.

Do not wear gloves when you are working with a bench grinder, as it is very easy for material to get caught on the wheel and sucked in.  If a glove gets caught on the wheel, you will not have time to react and there is a very high likelihood of severe injury.  Grinders spin very quickly and it might seem intimidating for new users, but they are very safe if used properly.  

8. Check the Blade for Damage

Small dents or nicks in the blade are pretty normal as small rocks and other debris get chopped up during use.  However, if the blade is bent or has large dents or cracks in it, you will need to replace it.  A broken blade can actually break during use, which can cause serious damage to your machine, as well as being a major safety hazard to the operator.  A bent blade will not be in balance during use, and is much safer to purchase a new one that is guaranteed to be correct rather than attempting to fix the curvature yourself.  

9. Grind any Dents Out of the Blade

Grind the blade directly perpendicular to the grindstone until any dents or chips are mostly worn away.  They do not need to be completely removed, so a few passes over the grinder should be enough. Do not grind down too far or it will be difficult to restore the sharp edge that you need for cutting.  Removing too much metal can also throw the blade off balance, which we will touch on in step #12.

10. Match the Bevel Angle of the Cutting Edge

Before grinding away at the blade, be sure you are matching the factory specified angle for the cutting edge.  A 45-degree angle is pretty common, but if you are not sure, you can always check your user manual. You need to match this angle when you sharpen it, or the blade might not cut grass properly.

11. Grind the Bevel of the Blade

It’s time to actually grind the blade itself.  Keep the bevel angle of the blade pointing upwards and facing the grinding wheel.  Lightly press the bevel face onto the wheel and pull it across to evenly sharpen the entire blade.  It will likely only take a few passes to get it right, so be sure not to take too much material off.  

Once you have ground one end of the blade, spin it around and grind the second cutting edge, in order to match.  Use the same steps to ensure a sharp point.

12. Make Sure the Blade is Balanced

Once you have restored a taper to both sides of the blade, it is possible that more material was removed from one end than the other.  An off-balance blade will make the mower vibrate in a dangerous way and can even damage the motor, so balancing is a crucial step of sharpening.

Balancing a blade is a very easy process, and it only takes a common nail to do.  Simply hammer the tip of a long nail straight into a wall or another sturdy surface, and leave about an inch or two exposed.  Hang the blade like a picture on the nail, with the center bolthole as the hanging spot.  A balanced blade will stay perfectly even on the nail, while an unbalanced blade will gradually sink down on one side.  To remedy this, grind a little more off on the side that sank down until the blade sits balanced on the nail.

13. Reattach the Blade

Some blades are marked to make installation easier

Now that the blade is even and ready to cut again, you can reattach it back to the mower.  Secure it exactly the way it was, and the marking from step 3 should be helpful in remembering how to put it all back together.  If you have trouble, the owners manual should have instructions to help you out.

Repeated Lawn Mower Blade Maintenance

As you’re out trimming your yard, all that grass will quickly wear the blade right back down much more quickly than you might expect.  To combat this, it is best that you take the time to resharpen twice every season.  As you get more comfortable with the steps to sharpen the blade, don’t let good habits slip away; always wear personal protective equipment, and always detach the spark plug before doing any work on your machine.

But if sharpening the blade is no longer an option and the machine has seen better days it could be time to replace the mower. If you need help finding the best mower for this season then check out Acme Tools lawn mower buying guide. They cover the newest and highest rated mowers in the market this year.

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