How to Sharpen Lawn Mower Blades | Step-by-Step Guide

When a lawnmower mows continuously, it causes the blades to become dull and less efficient. This creates unclean cuts, and the lawn may look untidy. Therefore, sharpening your lawn mower blade is an important task to ensure a clean, precise cut, resulting in a healthy and beautiful lawn. In this step-by-step guide on How to sharpen lawn mower blades, we’ll walk you through the process of sharpening your lawn mower blades. With a few simple tools and a little patience, you can keep your lawn mower blades sharp and your lawn looking beautiful.

Overview of sharpening Lawn Mower Blades

Signs that Your Lawn Mower Blade Needs To Be Sharpened

How often you need to sharpen your lawn mower blades depends on usage and other factors, but your lawn can also be an indication of whether the blades need a good sharpening.

• Ragged cut: Your cut will look uneven, as if one side of the mower is lower than the other.
• Uncut grass: The lawn mower is mowed, and parts appear to be pushed down instead of being cut, indicating a dull blade.
• Uneven height: Pruning grass requires sharp lawnmower blades, as uneven blades may indicate insufficient sharpness for clean, efficient grass cutting.
• Nicked blade: Blade’s edge has noticeable nicks and dents

How to Sharpen Lawn Mower Blade

Step 1: Prepare Tools and Materials

• Safety gloves, glasses 
• Socket wrench, long-handled wrench
• Blade balancer 
• File or bench grinder 
• A vice (if using a bench grinder) 

Step 2: Disconnect the spark plug or battery

• The first step is to remove the spark plug from the front of the engine to eliminate the possibility of the engine starting. Anyone who owns an electric lawn mower should make sure to unplug it or, in the case of a cordless mower, remove the battery.

Pro Tip: We recommend always removing the spark plug when working with the blade. 

If the piston is at the top of the compression stroke, a small amount of pressure on the vanes can push the piston over the “hump” and into the power stroke. If this happens, the blade will swing back and forth, and you risk breaking your hand!

Note: You need to put on your safety gloves and safety glasses or goggles to protect your hands and eyes.

Step 3: Turn the Mower Upside Down to Remove the Blades

Turn the lawn mower onto its side with the air filter and carburetor side oriented upward. This prevents oil and gas from dripping into the air filter.

Pro tip: The carburetor, with throttle cables, should be kept facing up when starting a mower to prevent oil leaks. Gas caps with air holes may leak gas, so work outdoors or use a rag for cleanup. 

Mark your blade

Mark your blade with spray paint before removing it so you know how to reinstall it.

• NOTE: Our lawn mower repair experts say the biggest mistake homeowners make is installing the blades upside down after sharpening them. The blade won’t cut – and they’ll go crazy trying to figure out why!
• Pro tip: Have a spare blade ready when you need to replace it.

Start to Remove the Blade

1. To clamp the blade, place a short 2×4 or a piece of 3-inch pipe between the blade and the deck. 
2. Use a long-handled wrench to loosen the bolt (or nut). 
3. Turn counterclockwise to remove screws and blades.

• NOTE: You will usually find a single bolt or nut holding the blade in place. It’s so tight that you have to clamp the blade to loosen it. The 2×4 method we indicate is simple, fast, and safe. Remember that Don’t use your feet!

After removing the blades, place the movers back on all four wheels until you are ready to install the blades.

 Pro Tip: For an easier solution, you can also check out the Sharpal Knife Sharpener

Step 4: Inspecting and Cleaning the Blade

Before proceeding sharp, check the blade and decide if it’s good enough to be sharpened or if it should simply be replaced. Check it and clean it with a wet microfiber cloth or a penetrating cleaner. If there is severe damage, such as cracks and dents, you should consider purchasing a new item. If it looks dull and chipped, it’s worth sharpening it.

Step 5: Sharpen the blade

Method 1: Use Clamp and File

A flat file is a simple tool used to sharpen a dull blade. Secure the blade in a vise. Apply pressure to the file and move it perpendicular to the edge of the blade to sharpen away imperfections in the metal and refine the shape of the existing edge. 

Reposition the blade in the vice to complete the other side after you’ve completed one side. Although it takes longer than filing by hand, the method is effective.

• Pro tip: Use a hand file to make your blade sharp. Lawn mower blades are made of relatively soft steel. Most things can be sharpened in less than 50 strokes with a clean, sharp Mill Bastard file that is at least 10 inches long.
• Note: Grinders also work and are faster (pros use them). But, they are more difficult to control and can cause the blade to become damaged.

Method 2: Use a Bench Grinder

The fastest way to sharpen a blade is with a bench grinder. Keep the blade perpendicular to the rotating wheel as you move the blade along the cutting edge at the angle of the existing bevel. This creates a spark, so it is necessary to wear safety glasses. If the blade gets too hot, submerge it in a bucket of water to cool it.

Pro Tip: When using this method, you need to be careful not to oversharpen the blade or remove too much metal. Over-sharpening creates a thin edge that is easily damaged, and removing too much metal shortens the life of the blade. 

Method 3: Use a Drill and Blade Sharpening Stone

A blade sharpening drill works similarly to a bench grinder but on a smaller (and cheaper) scale. It’s faster than filing by hand, and the drill’s stone is designed to hug the edge of the mower blade, allowing for easy and error-free sharpening.

Once both sides are sharp, check the balance of the blade by hanging it on a nail through the screw hole. If hung horizontally, it can be reinstalled. If one end hangs lower than the other, move a little further away from the edge of that end until the blade is balanced on the nail. This ensures the smooth operation of the lawnmower.

Step 6: Check the blade’s balance

Check the balance of the blade before reinstalling it, as a bent blade can wobble and crush the mower’s engine. Place the blade balancer on a flat surface and use the center hole to place the blade on the balancer. 

As the blade is dipped, use a file, whetstone, or grinder to remove metal from the trailing edge (not the cutting edge) on the heavier side toward the end of the blade.

• Pro Tip: You can also check the balance by hanging the blade on a nail in the wall by hanging it through the center hole. Remove material off the side that has a blade that tilts.

Step 7: Reinstall the blade

Use the mounting nut to reinstall the blade onto the spindle underneath the mower. Hold the blade with one hand while tightening the nut with a socket wrench. Turn the mower over, reconnect the spark plug wire or power source, and get to work!

• Note: Our Lawn mower sharpening experts say that the second most common mistake is over-tightening the bolts. This can cause a loose blade might cause the mower to start more slowly and, at times, cause timing problems with the engine.

Benefits of Using a Sharp Mower Blade

When you use dull mower blades, they don’t just result in a messy lawn;they can also cause the grass to turn brown or look ragged. This is because these blades will rip and tear the edges of the grass blades, leaving the grass more susceptible to various diseases.

According to Richard Hentschel, University of Illinois Extension instructor, with dull blades, today’s rotary mowers shred the grass instead of cutting it. After 24-48 hours, the shredded grass blades will resemble straw in color and appearance. These shredded grass leaves cannot truly heal, exposing the tissue to pathogens.

Here are some benefits when you use a sharp lawn mower blade:

Enhanced Aesthetic

• Eliminates ragged or uneven grass tips
• Create a more attractive lawn.

Improved Lawn Health

• Clean cuts prevent grass diseases.
• Encourages even growth and reduces stress on the grass.

Time and Cost Savings

• Improved blade performance in cutting grass
• Reduces the need for frequent mowing.
• Saves money on fuel and maintenance.

Environmental Benefits

• Promotes better water retention and soil health.
• Lower carbon emissions due to reduced mowing frequency.

Safety

• Decrease the risk of flying debris.
• Enhances operator safety by reducing blade tension.

FAQS on How to Sharpen Lawn Mower Blades

Why is it important to sharpen lawn mower blades?

A dull mower blade can tear and pull at grass blades, leaving irregular cracks that both weaken the plant and promote fungal growth and other grass diseases. Sharp blades, on the other hand, cut cleanly, allowing plants to heal and recover quickly. Improving the sharpness of your lawn mower blade will help you get the job done faster and put less stress on your lawn mower.

How often should you sharpen your lawn mower blades?

Typically, you’ll need to sharpen your lawn mower blades once or twice a year. We recommend sharpening your lawnmower in the spring when preparing your lawnmower for the coming season. If you have a large garden or require frequent mowing, you may need to sharpen it again after 25 hours of use.

Should you spend money sharpening your lawn mower blades?

If you’re unsure of your skills, it might be worth taking it to a workshop and having it sharpened by a professional because keeping your blades sharp can save you money and hassle in the long run.

Final Thoughts

Sharpening your lawn mower blade is an important task that should be done regularly to keep your lawn healthy and looking great. By following the correct steps, you can ensure that your lawn mower’s blades are sharp and balanced for a better lawn mow. So don’t neglect this important task – take the time to learn step-by-step how to sharpen the lawn mower blades, and enjoy a beautiful, healthy lawn all year round!