How to sharpen a lawn mower blade

This DIY Guide will teach you how to sharpen a lawn mower blade.  If you have questions or comments please feel free to contact us using the comments section below or our contact form.


Is your lawn mower tearing off the lawn grass blades instead of cutting it? Does your lawn look like it has been chewed by a goat, in spite of being cut by the lawn mower?

Wait, do not pull your hair by the root. Help is at hand. We will teach you how to sharpen a lawn mower blade at minimum price and effort.


TOOLS REQUIRED:

    1. Safety Glasses
    2. Work Gloves
    3. Flat File and/or
    4. Hand Grinder
    5. Blade Removal Tool
    6. Bench Vise and/or
    7. (2) Adjustable C-Clamps
    8. A well lit sturdy work surface
    9. A standard socket or wrench set

LAWN MOWER BLADE SHARPENING PROCEDURE:

STEP 1:

JpegDisconnect the Spark Plug wire.

Before you put your hands under the mower deck you need to disconnect the spark plug wire! 

If you start twisting that blade around and you’re gonna start the engine like one of those old WWI fighter planes and chop off your little digits.

 

 

 

 

 

 

 

 


STEP 2:

ACCESS THE MOWER BLADE

mower accessOnce the plug is disconnected, put on your gloves and lets take a look at the blade.

Most folks tip the mower over on its side. Which is fine. But what we like to do is to angle the mower backwards, keeping the rear wheels on the ground and the spark plug pointing upward.

If you can place the mower on an elevated surface, such as a work bench; you may find it even easier to accomplish this particular task. Once the mower is tipped backwards, secure it in place.

 

 


STEP 3:

SECURE THE BLADE

DECK UNDERSIDE

 

 

 

 

 

 

 

 

 

 

no woodNote: We’ve seen folks jamming a block of wood into the discharge port to “secure” the lawn mower blade. We DO NOT recommend this method and here’s why.

First off, if you’ve disconnected the spark plug, the engine will not start. Second, if you do end up wrestling with one of the blade bolts, you could end up bending the blade, damaging the blade adapter or even worse damaging the deck.

If you need to prevent the blade from turning, consider holding onto it with your free hand (please wear gloves).

If you’re not comfortable with that, or if the blade bolt is being stubborn, consider picking up a blade removal tool or perhaps applying a couple of c-clamps to either side of the blade to prevent if from moving.


STEP 4:

REMOVE THE BLADE

Jpeg

Your blade will be held on with one or more bolts (depending on the model, type and brand of mower).

It’s important to have the correct size socket to remove the bolts. Stripped out bolts are a pain to remove and can be costly to replace if you have to have a technician remove it.

Remove the bolt(s) the blade and the blade adapter if applicable. A good way to avoid misplacing the bolts is to thread them back in their respective holes.

 

 

 


STEP 5:

INSPECT THE BLADE

To conduct an effective inspection, you may find it necessary to clean the blade with a wire brush. Inspect the blade for wear and damage. Here’s what you might find:

Nicks: Nicks are to be expected and can be dealt with when sharpening the blade. It’s the deep ones with the little cracks running from the nick that mean its time to get a new blade. If you’re not sure, take a plain, old number two pencil and color in around the nick. Now wipe off the graphite and lets see if any cracks stand out.

 

 

JpegBends: If the blade is bent, you’ve hit something “hard”. Like, real hard. The true hazard lies not in the fact that the blade has bent but rather the possibility that something else may have bent as well. Something like the engines crankshaft. If the blade is bent, replace it, but have the crankshaft inspected by a technician before using the mower again.

 

 

JpegBreaks: If you’ve hit something hard enough to break the blade…dang. If you’re not going to dig up whatever it is you keep hitting, then get some blaze orange spray paint and mark it! If the blade is broken or cracked, replace it. And you should probably get that crankshaft inspected by a technician before starting the mower again.

 

 

 

 

Cracks or Fissures: These can result from erosion or weaknesses in the steel. Any signs that the integrity of the metal has been compromised means replace the blade. Believe me, you don’t want that metal flying off of the blade at 3000 rpms.

Lawn Mower Blade ErosionErosion:  The whole reason for needing to sharpen the blade is erosion. And the level of erosion may differ greatly depending on the type of soil your grass grows out of. Sandy soil? Hang it up, chief. You’re poor blades never stood a chance. But when we talk about erosion here, what we’re really looking at is not the cutting edge, but the area of the blade opposite of it. As particulates pass over the surface of the blade, they begin to wear down and thin out the steel behind the edge. Slowly, but surely the metal will thin and disappear. And by disappear, I mean fly away like tiny little throwing stars. Any sign of rear blade erosion and its time to replace the blade.

 

Worn Lawn Mower Blade

 

 

 

 

 

 

 

 


STEP 6:

Sharpen the blade

SHARPENING TOOLS

Flat Hand FileHand File

A hand file works, but it can be time consuming. And like the hand grinder, there is a knack to getting it right. But some folks swear by it and that’s that. So, file on..”filer”. Don’t let anyone stand in your way!

 

 

 

 

 

 

 

 

Bench Grinder

Bench Grinder

If you have a bench grinder, you’ve just saved yourself some time. Once again, with the progression of the grinding wheel moving against the edge, pass the blade evenly and slowly across the wheel. Once again, take your time.

 

 

 

 

 

 

Hand Grinder

Hand Grinder

Hand Grinder in Action

Our personal favorite is the hand grinder. It’s fast, powerful and there’s a bit of an art to using it. Plus, all those sparks flying all over the place is just plain cool. Not everyone can use the hand grinder effectively; it takes practice.

 

 

 

 

 

 

SHARPENING YOUR BLADE: 

The majority of cutting is done with the outer inch of the blade. Because of this, a curve will eventually form on the cutting corner. You can grind the edge of the blade flat, but you’ll be greatly reducing the life expectancy of the blade. Best to keep the blade sharp as possible and monitor the deterioration of the outer edge. When we start looking like a butter knife, it’s time to replace it.

Lawn Mower Blade in ViseFirst, we want to secure the blade in place. If you’re fortunate enough to have a bench vice, lock it in there at an angle that allows you complete access to the cutting edge.

 

 

 

 

 

 

 

 

 

 

Bench Vice

bench blade clampIf you don’t have a bench vice, you may consider locking the blade to the work bench with adjustable “C” Clamps. It’s always a good idea to use a nail or bolt to hold the center hole in place as well. This will help prevent slipping.

 

Working towards the edge, you’ll want to take your time. Try to match the original angle of the edge (if there’s enough of the original edge left to match).

Blade on Bench Grinder

Remember, we’re not going for a razors edge here. When it comes to how much to remove: less is more. The thinner the edge, the faster the blade will wear out.

 

 

 

 

 

 

 


STEP 7:

CLEANING UP THE EDGE

blade slag fileGrinders will often leave a thin, curled “bur line” on the back edge of the blade.

The good news is that its easy to remove. Your flat file is a great way to knock the bur off.

 

 

 


STEP 8:

BALANCE THE BLADE

Installing an imbalanced blade will very quickly reveal which parts of your mower / engine are weak and ready to break when it starts shimmying and shaking like a teeny-bopper. So, before we put the blade back on the mower, we want to make sure that its balanced.

Simple

Lawnmowerpros.com offers affordable blade balancers, like the 
OREGON 42-100 BLADE BALANCER
. This handy little device will help ensure that your blade is balanced before re-mounting it to your mower.

 

 

 

New Fangled

wall mounted blade balancer

We encourage you to go to lawnmowerpros.com and order a blade balancer. This nifty little guy will mount right there on the wall of your shop or sit right there on your work bench. You just set the conical point in the center hole. The magnets grab hold. If the blade stands firm, it’s balanced.

If not, it’s back to the grind stone.

 

 

 

 

 

Old School

Get yourself a big old nail and drive it into your wall. Hang the blade on it and see if it tips. If it does, grind grind again. If not, we’re ready to re-install it on your mower.

If you’re not comfortable sharpening your blade or don’t have the proper tools you can always run over to your local shop and have them sharpen your blade.  Depending on the blade this will run between $5.00 and $10.00 each.


STEP 9:

RE-INSTALL YOUR BLADE(S)

Repeat the previous steps in reverse order.  But before you reinstall your blade, this is a great time to take a look at the state of your mower deck. Using a scraper remove any grass build up.


As you can see, sharpening a lawn mower blade doesn’t require any fancy tools or skills.  It just requires a minimum of tools which you probably have sitting around collecting dust anyway and a little time.

I can already hear your lawn saying “thank you”.

-Jack

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Jack Hayes

Jack Hayes

Jack Hayes is the Head of Internet Marketing at LawnMowerPros and the editor of this blog. You can often find him creating featured articles, DIY guides, custom graphics and much more.