How to Sharpen Lawn Mower Blades?

The blades of a mower are arguably the most important component. When they are dull, dinged, or rusted, your lawn mower’s harvest rate will start to plummet, leaving you with an unkempt lawn full of shaggy edges.

Sometimes it’s hard to tell how sharp your lawn mower blades are. Especially if you have a heavy riding lawn mower where you can’t just tip it or lean over to see what the blades look like.

What Are Signs Of Dull Lawn Mower Blades?

One of the most telltale signs that your lawn mower blades are dull or dinged is stray strands of uncut grass left behind after you make a pass. Now, this could be expected if the grass is wet or you were perhaps going a little bit too fast. If you are making pass after pass at a reasonable pace and your lawn is dry, only to see stray patches of tall grass, it could mean your blades are getting dull.

Signs That Lawn Mower Blades Are Dull

  • Ragged Torn Blades Of Grass
  • Stray Grass Left Behind
  • Blades Of Grass Are Flattened Instead of Cut
  • Obvious Knicks and Dings On The Lawn mower Blades
  • Rust On The Lawnmower Blades

It’s important to note that a strange vibration or distressing noises after hitting something like a large tree branch of a stone in the lawn, might be a sign of a bent, cracked or fractured blade. This is a sign that the blade itself is badly out of balance and likely needs total replacement rather than sharpening.

If you’ve seen obvious signs that your lawn mower blades are dull, but not damaged or out of balance, there are a few ways to sharpen them.

How To Safely Remove Dull Lawn Mower Blades

  • Step 1: Disconnect the lawn mower’s power source by either removing the spark plug wire or removing the battery. If you have a gasoline-powered lawn mower, you might want to also drain the fuel to avoid spills.
  • Step 2: Put on protective eyewear and gloves.
  • Step 3: You can gently turn a push mower on its side or lift a riding lawn mower with a mower jack. Just make sure that the air filter and carburetor are up.
  • Step 4: Locate the nut that connects the cutting blade to the mower deck. Use the correct size wrench to turn it counter-clockwise and loosen until the mower blade comes free. Then use a spot of spray paint, a permanent marker or a piece of tape to mark the top and bottom of the lawnmower blade.
  • Step 5: Use a dry shop rag or cloth to gently wipe the blade clean. The goal is to remove any debris that might hide dings and chips in the blade edge. For an especially corroded or gunky blade, you might need to use a nylon brush and a little penetrating oil like WD 40.

Securing A Dull Lawn Mower Blade

To effectively sharpen a dull lawn mower blade, you need to be able to produce a consistent edge. This is nearly impossible to do with your bare hands. Worse still you risk taking away too much metal, which could compromise the integrity of the blade or shorten its lifespan.

Ideally, you want to clamp the dull lawn mower blade in place with either a bench vice or a pair of C-clamps. That way no matter what sharpening method you choose, you can trust that the dull lawnmower blade will stay in the correct orientation.

Choosing The Best Sharpening Method For Dull Lawn Mower Blades

There are generally three different ways to properly sharpen dull lawn mower blades.

  • By Hand With A Mill File
  • A Drill-Powered Blade Sharpener
  • With A Bench Grinder

It’s important to note that you are not trying to make the blade “Razor Sharp.” This will just leave the blades more vulnerable to dulling and might take away too much structural integrity. Most modern lawnmowers spin the blades at such high RPMs that “Butter Knife Sharp” will be sufficient to harvest the maximum amount of grass.

How To Sharpen Lawn Mower Blades With A Mill File

This is arguably the most time-consuming method, as it requires a lot of hand-precision, and a fine-toothed mill file or a manual grindstone. However, it will take away the least amount of material from the cutting blades, which translates into a longer blade life.

  • Step 1: Put on protective eyewear and gloves. Then lock the lawnmower blade in place with a bench vice or C-clamps.
  • Step 2: Hold the mill file at roughly a 45-degree angle.
  • Step 3: Carefully push the mill file in one direction along the blade. You aren’t going to “Saw” the pressure needs to be just enough that you feel the teeth of the mill file striking the metal of the blade. Dings and rough spots might be multiple passes to blend them in.
  • Step 4: After you are done sharpening one side, switch the blade over and repeat on the other edge. You should be able to properly sharpen one blade edge in 50 to 60 strokes.

How To Sharpen Lawnmower Blades With A Drill-Powered Blade Sharpener Or Rotary Tool

  • Step 1: Put on protective eyewear and gloves. Then lock the lawnmower blade in place with a bench vice or C-clamps
  • Step 2: Install a blade sharpener into a rotary tool, corded, or cordless drill. Make sure it has at least a 1/4-inch shank.
  • Step 3: Activate the rotary tool or drill and place the grinding edge over the edge of the mower blade
  • Step 4: Carefully apply medium-pressure as you move the sharpening bit back and forth along the blade edge. It should take 4 to 5 strokes to properly sharpen the blade. Though you may need to do some touch-up work around dings and chips in the blade edge.
  • Step 5: Turn the lawnmower blade over and repeat the process.

How To Sharpen A Lawnmower Blade With An Angle Grinder

This is arguably the fastest way to sharpen a lawnmower blade, though it will take away the most material

  • Step 1: Put on protective eyewear and gloves. Then lock the lawnmower blade in place with a bench vice or C-clamps.
  • Step 2: Align the grinder at a 45-degree angle to the mower blade and activate it.
  • Step 3: Carefully pass the grinder back and forth against the edge of the blade, following the existing angle as best you can. Give extra focus to blending out dings and chips.
  • Step 4: Turn the lawnmower blade over and repeat the process.

Once you are done sharpening the lawnmower blade, you can reinstall it back into the cutting deck. This is also a good opportunity to double-check any belts and other components that might show some wear and tear. It’s better to replace a belt while you already have access to the mower deck than it is to have it snap on you a week or two later.


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