DIY Precision Lawn Mower Blade Sharpener. How sharpen mower blades

How to Sharpen Mower Blades for a Better Lawn

If you’re as passionate as we are about keeping your lawn lush, green, and healthy, you might be aware that dull mower blades pose a danger to your lawn’s health. Your trusted experts at Outdoor Concepts are here to help. Here, we’ll cover the effects of mowing with a dull blade, as well as red flags to watch out for. Finally, we’ll share some tips for proper sharpening techniques.

THE DANGER OF DULL BLADES

You might be wondering if you can put off sharpening your blades. After all, you need to cut your grass, and you might not have time to do both. While we get that your time and energy are valuable and limited, we’d recommend NOT mowing with dull blades.

You see, when your lawn mower’s cutting edge spins, if it’s properly sharp, it slices cleanly through each blade of grass. But a blunt blade catches the grass, tearing it rather than slicing. When this happens, you end up with shredded grass. Your lawn will take longer to heal, as each blade of grass is like an open wound. During this longer recovery period, your lawn is much more susceptible to drought, heat, and pests. In severe cases where the lawn is repeatedly mowed with dull blades, the grass can even begin to die.

It isn’t just your lawn that you need to worry about, though. If you consistently mow with dull blades, you’re overtaxing your lawnmower. After a while, you increase the wear-and-tear on your belts, your PTO system, and even your engine.

These issues are avoidable, thankfully. But how?

BLUNT BLADE WARNING SIGNS

To avoid damaging your lawn and your mower, it’s important to keep an eye out for the following four signs.

• You might see the tips of your grass turn white or brown a couple of days after you’ve mowed. If so, take a closer look. You’ll probably see that the grass ends look shredded, a bit like torn cloth. This is the most common sign of dull blades and the easiest to recognize.
• Whole clumps might be yanked out of the ground. This can happen if you have extremely dull blades that can’t even shred grass; the blunted cutting edge just catches and yanks out clumps.
• Your cut looks uneven, as if one side of your mower is lower than the other. This is a sign that parts of your blade have dulled more quickly than the rest.
• Your engine sounds like it’s struggling, or mowing is taking longer than it normally would.

CHECKING YOUR BLADES

If you’re seeing any of the above red flags, put mowing on pause and take a look under the deck. If you have a push mower, empty the gas tank or run your engine until the tank is dry, then disconnect the spark plug and tip it onto its side, keeping the carburetor and air filter pointing up.

Inspect the blade. If it looks bent or warped, or if the cutting edge is missing chunks, it’s time to replace it. But if there are only a couple of minor nicks, you should be good to sharpen it up and save a few bucks.

MOWER BLADE SHARPENING TIPS

Before you start sharpening your mower blade, be sure to wear the proper safety equipment. At the very least, don a pair of work gloves and some safety goggles.

Once you’re ready to sharpen your blade, remove it and secure it in a vise. If you’re doing this the old-fashioned way with a file, press the file firmly against the blade, matching the angle of the cutting edge, and sharpen it in a single direction. Don’t drag the file back and forth, and don’t sharpen any areas aside from the cutting edges on either end. After every ten strokes, test the blade with your hand.

If you’re using a drill-powered blade sharpener, place the grinder over the blade’s edge. Be sure that the grinder’s guide (the flat piece) is against the back side of the blade and that the cutting edge is in between the two pieces of the grinder. With these sharpeners, you don’t have to worry about finding the right sharpening angle since they adjust automatically. Shift the grinder back and forth across the blade’s edge four or five times with moderate pressure. Then test the blade against your hand. 1

Your freshly sharpened blade should feel about as sharp as a butter knife and shouldn’t break the skin. Any sharper and the blade will dull far more quickly, forcing you to sharpen and replace your blades more often. 1

When you re-install your freshly sharpened blade, make sure the angled side faces up toward your mower deck. If you install the blade upside down, it won’t cut properly.

Lastly, before tightening the blade down, make sure it’s perfectly centered and balanced. Mowing with imbalanced blades can stress your engine and harm your mower deck. A couple of ways to know if your blades are imbalanced is if you’re experiencing a lot of vibration when you mow or if patches of grass on one side of the mower look worse than those on the other side. 2

How often should you sharpen your mower blade? It can vary a bit depending on your goals and how much you’d like to invest in the health of your lawn and equipment. However, a good baseline is to sharpen them after every 20-25 hours of mowing.

STAY SHARP

Now that you know the dangers, warning signs, and ways to sharpen dull blades, you’re well-equipped to keep your lawn and your lawnmower in great shape.

But you never know what life’s going to throw your way. It’s always a good idea to keep a couple of spare blades on hand just in case. Stop in at Outdoor Concepts! We’d be happy to help you find the right blades for your machine. If you need it, we can also sharpen your mower blades for you.

This article was updated May 11, 2023

Introduction: DIY Precision Lawn Mower Blade Sharpener

Recently, when it came time to replace my old mower blades, I looked for DIY lawn mower blade sharpener ideas on YouTube. I wanted a design that wouldn’t take up much storage space, but that could be quickly easily setup and used. I found one design that I thought had possibilities, so I decided to make one. Here are links to the original by Clean Green Lawn Service LLC a modified version by Michael Krailo.

To have the blades sharpened “professionally” locally it costs 19, about two thirds the initial cost of new blades (as of June 2022). I grew up on a farm and we always sharpened our own bladesand I still do to this day.

Most of the nuts and bolts for this project I had on hand already, so I was able to keep my new purchases around 26. I was able to pick up an inexpensive angle grinder (9.99) from Harbor Freight with a “Super coupon”, three foot of the aluminum square tubing (10.69) and a horizontal hold down clamp (5.26) from Menard’s. The grinder needed for this project can be small because you don’t need very much grinding power to sharpen mower blades. Plus, I already had a grinding flap disc from one of my other grinders.

Note: I was asked why I chose a flap disc for this project rather than a solid hard disc. A flap disc produces a stronger cutting edge than a solid disc. For example, a flap disc “rounds over” the cutting edge and leaves more metal; a flat file creates a “strait” edge; a solid disc results in a weaker edge because it “grinds out” metal to create an edge.

The sharpening process usually involves three light passes per side and then I check the blade balance. It typically takes me under ten minutes to sharpen and balance a set of blades (two).

Using the videos, I first built a prototype and found that there was too much rotational “play” even when the joints were moderately tight. I eliminated this problem using ¾” aluminum square tubing in place of the ½” steel square tubing used in the original video. I chose aluminum rather than steel for a couple of reasons: lighter weight and because I planned to store the sharpener in my garage (no rust from humidity changes).

I normally store my sharpener in an upright position (Figures 1a, 1b 1c), so the space required is roughly 10”W x 12”D x 15”H (Figures 2a 2b).

Note: A short video was added on 8-10-22 as requested, as well as a Figure 9 with two screenshots from the video.

Note: To view photos original size in this Instructable when uploaded, you may need to position the cursor near the bottom left of the photo and you to see a “Download Original” icon. Press it and the photo will open to it’s original size. If the photo is white in the bottom left corner, you may not be able to see the icon, but you should still see the “Download Original” pop up.

Tools

Step 1: Determine Bevel of Mower Blade

The vast majority of lawnmower blades come from the factory with a 32 degree bevel (profile). However, it is important to verify your blades’ profile before building this sharpener. Even an error of two degrees will be noticeable in the end results. Most dealerships recommend a blade profile somewhere between 30 45 degrees, so… If your profile measurements are off slightly, your first sharpening may take a bit longer since you will be changing the blade profile slightly. When I used a protractor (Figure 3) to measure my blade profile it was 32 degrees.

Step 2: Create Base

Starting with the 4”x4”x12” piece of fence post (base), I cut a 32 degree profile on one end with my miter saw (Figure 4a). In the YouTube videos they cut their other ends to 32 degrees 40 degrees respectively (“backward slant angle”. Figures 4b, 4c 4d). After trial an error, I decided 10 degrees was more comfortable for me when sharpening.

Tip: After building a prototype, I noticed that the bevel profile angle wasn’t correct when I tested with the angle grinder. I discovered this was due to my miter saw gauge being off by almost 2 degrees around the 30 degree marks. I corrected this by using my shop protractor to set the proper angle (32 degrees) before sawing the 4”x4”x12” base.

Step 3: Create Articulating “Arms”

From the prototype I decided that there was too much rotational “play” even when the joints were tightened moderately. I eliminated this problem using ¾” aluminum square tubing (Figures 5a thru 5d). I chose to use aluminum rather than steel due to weight and because I planned to store the sharpener in my garage.

For the articulating “arms” I cut two 12 inch sections of ¾” aluminum square tubing and drilled ¼” holes in three of the ends and drilled a 5/16” hole in the last end. After “deburring” the drilled holes and cut ends, I joined the two sections of square tubing using a ¼”x2” bolt, three ¼” washers and a ¼” lock nut (Figure 5c). I used a ¼”x4″ lag screw and four ¼” washers to mount the square tube arm to the 4″x4″x12” base 2 ½” down from the top (Figures 5a 5b). The articulating arms were attached on the right side of the base (Figure 5a).

Before mounting the tubing to the grinder, I attached a baseboard to the bottom of the base (used when clamping sharpener to a bench/table). The baseboard was a ¾”x7”x9” piece of surplus wood I had on hand and I used five 2” deck screws. I then mounted the square tubing to the grinder using a M8-1.25 x 60 bolt, two washers and two M8-1.25 coarse nuts and placed a M8-1.25 coarse nut on the bolt end that screws into the grinder (Figure 5d).

Step 4: Mower Blade Clamping Base

Next, I created the mower blade clamping base using a ¾”x5”x6”, a 3/4”x2”x6” hold down clamp mounting board and then mounted the a horizontal hold down clamp with four 1/8”x1” lag screws (Figure 6c).

Since newer mower blades are “stamped” into their final shapes during manufacturing, the cutting edges/ends usually are not parallel to the blade center (Figure 6a). The mower blade clamping base will usually need to be slightly rotated counterclockwise when mounting to the 4”x4”x12” base (Figures 6c 6d).

I clamped a new mower blade on the mower blade clamping base (Figure 6b) and positioned on top of 4”x4”x12” base to determine the correct centering the blade bevel with the center of the grinder wheel. I drew a line on the 4”x4x12” base (to align afterwards) and then set the grinder down. I finished by mounting the mower blade clamping base using five 2” deck screws (Figures 6c 6d).

I hope you find this Instructable useful.

How To Sharpen Lawn Mower Blades

One of the biggest challenges in maintaining a pristine lawn is mowing it. The warmer months mean it’s time to get each blade sharp and ready to shear those grass blades down.

Detaching your lawn mower blade will depend on your model (push mower or ride-on), but the methods for sharpening are similar. You can either clamp the blade in a vise, then file using a mill file, or work using a drill with a sharpening stone attached.

Ready for mowing season? Here’s how to sharpen lawn mower blades – after all, if you invest in the best quality lawn mower. you’re going to want to take care of it!

Why Sharpen Lawn Mower Blades?

You need to sharpen your mower blades to ensure a clean job when you cut grass. Dull blades will snag on the grass and rip it out, damaging your lawn. This will also put your lawn at risk of diseases like fungal infestation.

For the cleanest, most efficient cut while mowing, you’ll need to make sure your blades are sharp. And while you can always have the blades professionally sharpened, you can do a DIY job if you’re up to it! This is especially true if you use your mower as often as say, a professional lawn mowing service would.

Does Your Lawn Mower Blade Need Sharpening or Changing?

Here’s a tricky question – do you just need to sharpen, or should you change your lawn mower blade entirely? To answer that, check your blade at the start of mowing season. If the edge is simply dull and flat, then you only need to sharpen it. It’s the same if you notice uneven patches or tears in the grass.

On the other hand, if there are nicks or cracks in the blade, then you can’t simply sharpen it to fix it. This is the same case if there are bends or warping. In this situation, you’re better off changing the blade out to a new one.

How Often to Sharpen Mower Blades

Ideally, once every other month. But always check the blade to see if it needs sharpening. If you mow very often, it may need filing more frequently.

Things To Know Before You Sharpen Your Lawn Mower Blade

Do not aim for the sharpest blade possible – that’ll wear your blade too thin, causing it to perform inefficiently. You’ll also need to sharpen it more frequently to retain that razor-sharp edge.

Instead, aim for “butter knife sharp” so that your blade holds up longer.

Also, check what tool you’ll use to sharpen the lawnmower blades. There are two main tools you can use:

Which you use depends on your budget and what’s available to you.

Lastly, it’s not possible to sharpen a mower blade without removing it. Not only will you do an inefficient job, you might also hurt yourself in the process.

Sharpening Lawn Mower Blades

Always start by unplugging the spark plug and removing the spark plug wire. This means your mower won’t accidentally turn on and injure you while you’re working.

You should also use appropriate protective equipment, such as goggles and gloves.

Removing the mower blade

For a push mower, you’ll need to tip the mower onto its back or side. This will expose the underside of the mower, allowing you to access the retaining bolt securing the blade to the deck.

For a ride-on mower, lower the mower deck to its lowest setting so you can access the blade.

Use spray paint or a marker to note the correct orientation when reinserting the blade. The last thing you want is to install the blade upside-down – that’ll cause your mower to cut incorrectly.

How to sharpen lawn mower blades using a file

For those who don’t mow as often, or are trying to save money, the simplest tool you can use to get a sharp blade is a file.

Clamp the blade and check the angle

Insert the blade into a vise and clamp it to hold it in place. Check for the proper filing angle and move in one direction only, pushing across the top side of the cutting edge.

Take a 25cm (10in) mill bastard file and start running it along the sharp edge of the blade. Move in one direction and ensure you’re feeling the “cutting” action. Otherwise, your blade might be dull.

Use a balancer to check if the blade is properly balanced. An improperly balanced blade will cause damage to your mower in the long run.

Reinstall the blade

Reinsert the blade and tighten the main bolt. Ensure there’s no wobbling or looseness before reusing the mower.

How to sharpen lawn mower blades using a drill sharpener

There’s a heightened risk when using a drill sharpener due to the higher heat and speed involved. However, it’ll get the job done faster with less effort.

Clamp the blade and prep the drill

Again, secure the blade with a vise to prevent it from moving.

Attach the sharpening stone attachment to your drill.

Insert the cutting edge

Insert the cutting edge between the plastic guide and the stone. The guide should rest against the rear of the cutting edge.

Activate the drill and run the sharpening attachment along the correct side of the blade. Work until it’s sharpened. Then move to the other side.

It’s essential that you sharpen the same amount on each side so that the blade is balanced.

Use a blade balancer or a nail to test the balance of the blade. If one side lifts, file a bit more off the other side to even it out.

Reinstall the blade

Reinsert the blade into the deck and tighten the bolt.

Why Check a Mower Blade’s Balance?

Simple – an unbalanced blade will result in a poor cut. It’ll cause excessive vibrations and wobbling while mowing, which can damage the motor by causing undue stress. You could also cause damage to the mower deck.

Maintain Your Lawn with Sharp Lawn Mower Blades

Nobody wants a patchy lawn with ripped-up grass, so ensure you know how to sharpen lawn mower blades so they’re ready to slice through grass cleanly. This way, you can maintain a pristine lawn that you’re proud to show off to neighbours, visitors, and even yourself – no reason you can’t pat yourself on the back for your hard work!

Jamie Donovan

Jamie is an Australian horticulturalist and landscape designer. He enjoys writing about landscape architecture, garden design and lifestyle topics.

Jamie Donovan

Jamie is an Australian horticulturalist and landscape designer. He enjoys writing about landscape architecture, garden design and lifestyle topics.

How to Sharpen Lawn Mower Blades

Some time ago I was in a hardware store and an associate told me I should bring in my mower blades to have them sharpened as they “had a machine to make them razor-sharp.” I remember thinking, “Why would I want them to be razor-sharp? It’s a lawn mower for crying out loud. I’m not shaving with it. I am essentially trying to achieve the same look on my lawn as a pair of goats could do.”

So, here’s a quick article to show you how to sharpen your lawn mower blades to a reasonable honing. Considering you are cutting a plant which rabbits nibble, your 6.5 HP engine with blades spinning at 3,600 RPM is probably on the side of overkill.

How to Sharpen Lawn Mower Blades

There is one rule I always follow when dealing with sharpening blades of any type: Leather Gloves, Always! Whether you are using this technique on mower blades or a machete, put on a pair of heavy-duty leather gloves or some other kind of protection.

Tools You’ll Need

The tools you need. A metal file, leather gloves, and a vice.

• Leather Gloves
• Metal Flat File or Bench Grinder
• Socket Wrench
• Hammer\Mallet\Wood block
• Bench Vice

Step 1: Turn the mower upside down and take the blade off

Some folks will tell you that turning the mower upside down is bad, as the oil will go to places it is not supposed to. I usually do this at the beginning of the season and my oil has already been drained. However, I have done this before with oil in the engine and as long as I let it sit upright and settle for a while, there have been no issues.

Use the socket wrench and appropriate socket to get the work done.

Hint: The bolt is screwed in like normal (righty-tighty, lefty-loosey), but since the blade also spins it can be a pain to loosen. I find it helpful to use a block of wood or hammer to hit against the blade while I hold the socket wrench (gloved of course), rather than trying to torque down on the wrench and a potentially sharp blade.

Turn the mower upside down, preferably after you have drained last years oil and gas. Remove the blade with a socket wrench.

This mower blade is pretty bad off.

Step 2: Place the blade in a vice and sharpen with a file

I have two types of blades for my different mowers: one is a mulching blade (with the extra curve) and the other is a regular blade. The process for sharpening either blade-type is the same.

Run the metal file across the blade and away from you, at an angle, filing on the forward stroke as in the video and pictures shown below.

Note: If using a bench grinder, be careful how much metal you remove (See the next step on leveling). It can be easy to try to remove any imperfections in the blade which may remove more metal than necessary. This is fine as long as you keep both sides the same weight.

Run the file across the blade at an angle and away from you. Place pressure on the file on the forward stroke.

The angle of the file can be determined by the existing edge of the mower blade. Only one side needs to be sharpened.

Step 3: Repeat on the other side and check the balance

While I don’t believe your blade has to be razor-sharp to get the job done, it does need to be balanced. An unbalanced blade will lead to unwanted vibration and noise as well as increasing overall engine\mechanical wear. If you don’t have a handy tool for checking the level of your blade, just rest the blade across your finger, like checking the balance of a good knife. If you have severe leaning on one side, you will need to take off more metal, which means more filing.

Check the mower blade for levelness by using a tool which you can pick up at any hardware store in the mower section.

Step 4: Reattach the blade

Put the blade back on the mower the same way it came off. The concave side of the blade faces the grass. Be sure not to over tighten the bolt; you’ll have to do this again next year!

Happy Spring!

Mow Like a Pro: How to Sharpen Mower Blades

Sharpening your mower’s blades twice each season helps maintain your lawn’s health and appearance. Having a sharp blade cuts grass blades cleanly, allowing them to recover quickly. It can also help reduce your mowing time. Read on and learn about how to sharpen mower blades like a lawn professional.

Blades with Normal Wear and Tear

During its lifetime, a mower blade hits rocks, branches, and thatch on your lawn that cause nicks, dings, and curls. Dull mower blades rip the grass blades instead of cutting them cleanly. Ripped grasses are more vulnerable to lawn disease infections. If your blade is in fairly good condition, sharpening it can be a fairly easy task. To sharpen, clamp your blade in a vise and run a metal file along its cutting edge. Ensure that you are following angle of the factory bevel. Always remember to disconnect the spark-plug wire before removing the blade or performing other kinds of mower maintenance. Sharpen the blade every two weeks to maintain your blade.

Badly Damaged Blades

Blades that are more damaged require different care. They should either be replaced or sharpened on a bench grinder. Take the blade to the professionals at a service shop. There, they will inform you as to whether it’s time to spring for a new blade or they will sharpen it for you with a grinder. If you have your own personal grinder, however, you can sharpen the blade yourself.

To sharpen your own blade with a grinder, smooth out nicks by running the blade back and forth against the spinning wheel vertically. Doing this gives you a straight edge. It will be blunt, so next, support the blade on the rest plate. Then hold the blade at the angle of the existing bevel. Grind the blade’s length until its edge is sharp.

Balancing Act

Always be sure that the blade is balanced, as an off-kilter blade can damage your mower. You can purchase a plastic balancer at most local lawn-care centers for an affordable price. To use, start by resting the blade on the balancer. If one side dips down, it means the steel needs to be ground on that end—not from the cutting edge—in order to lighten it. After you have balanced the blade, it’s safe to bolt it back onto the mower. Now you’re ready to mow!

Questions? Call the professionals at Cardinal Lawns for advice or assistance with your yard.