Best Grit For Mower Blades – Sharpening For Lawn Mowers


A lawnmower’s blades are the most important part of the lawn care equation. Sharp blades are essential for cutting your grass neatly and minimizing the chances of lawn diseases. Of course, the blades do not stay sharp forever.

The best grit for sharpening mower blades according to the United States CAMI scale is between 60 and 80 grit. This refers to grinding wheels. For files, the first pass or two should be with a course file to smooth out burs and gouges. The next passes should be with medium to smooth.

In today’s article, we go over some solutions to this problem, as we identify the best grit to use for sharpening your mower blades. We will take a look at the best types of grinding wheels you can use, the best sharpening techniques, and a whole host of blade maintenance tips. Let’s go!

The Best Type Of Grinding Wheel To Sharpen Mower Blades

Grinding wheels are the most efficient method of sharpening lawnmower blades, especially when you look at alternatives like metal files and whetstones.

For steel and iron blades, aluminum oxide grinding wheels are the best. For softer metals like gray iron, brass, and non-ferrous, silicon carbide is better. Both of these types of wheels should be spun at a consistent speed ranging from 5000 to 6500 feet per minute.

That said, you should know that since grinding wheels are made from different materials, they are best suited to different kinds of blades. The appropriate grinding wheel will allow you to sharpen your blades as quickly, and as consistently, as possible.

Harder Material Blades

Blades made from steel and iron should (ideally) be sharpened with aluminum oxide grinding wheels. Aluminum oxide wheels are among the most common grinding wheels because they are ideal for a very wide range of materials including stainless steel, tool steel, as well as bronze and aluminum alloys.

Aluminum oxide wheels are renowned for their durability, which is beneficial for sharpening hard materials. This is the best choice if you don’t want to be replacing your grinding wheel frequently. Variations of aluminum oxide include ceramic aluminum oxide, vitrified aluminum oxide, and a host of others.

Softer Blades

For blades made of “softer” materials like gray iron, brass, and non-ferrous materials, silicon carbide is the way to go. Although harder than aluminum oxides, silicon carbide is great for these softer materials because of its highly abrasive surface.

Can You File A Mower Blade To Sharpen It?

One question I have been asked many times is how the average home owner or the lawn crew out in the field can sharpen a mower blade when a grinder is not an option. Can mower blades be sharpened using a metal file?

You can most definitely sharpen mower blades with a file. A grinder or a Dremel is simply a faster or more powerful alternative to files. The coarser files should be used to begin with the smoother or even medium files applied on the last several passes.

There are several types of files, but most of the common types will work just fine. There is really no need to get expensive files, though you may want to get one of the inexpensive kits that can be found on Amazon or at your local garden center. Most hardware box stores or small shops will carry them as well.

Simply make the first couple of passes with a coarse file and then use a medium or smoother files for the last few.

To get one of the sets we like here at LawnCareGrandpa.com, just visit the link below to see it on Amazon.

Can You Sharpen A Lawn Mower Blade With Sandpaper?

Though to some there is an obvious answer to this question, but I myself when younger had this same one. There are many that don’t intend on making lawn care a major hobby in their lives and questions like these can help them get through the necessary chores much quicker. So, can sandpaper be used to sharpen a mower blade?

Manually using sand paper, no matter the grit, is simply impractical to the point of impossible when sharpening a lawn mower blade. You need two things that manual sandpaper use cannot give you: speed or rigidity. Speed is accomplished by grinders and rigidity by files.

This is not to say that this line of thinking is all that off track. If you look at attachments to Dremel tools that make quick work of blade sharpening, you will find that the surface used is very similar to sandpaper.

For the cheapest and simplest option, a simple metal file will do the trick nicely. Besides, you should only need to sharpen your blade a couple of times per year and the task really only takes a few minutes.

Here an options that was listed above found on Amazon. I recommend the Dremel for those planning on using it quite often for sharpening blades and other projects. I use mine to make Christmas decorations.

The Best Grit For Sharpening Lawn Mower Blades

The grit (or grit rating) is a sharpening or filing surface’s level of abrasiveness. Different tools require certain grit levels for the best results. Lawnmower blades are no different. 

For lawnmower blades, we recommend grinding wheels or files with a 60-80 grit rating. This is generally known as the medium coarseness range and it provides a balance between removing materials and precision sharpening. Less or more grit can remove too little or too much material.

In the U.S., abrasives are graded according to the CAMI scale, where a material’s coarseness is assigned a number rating. The coarsest materials are assigned a rating of 12 while the finest abrasives are assigned a rating of 1200.

To see more articles about mower blades, I recommend my other ones here…

What Is The Easiest Way To Sharpen A Mower Blade?

Now that we’ve seen the best tools for sharpening your blades, let’s look at the best way to go about it.

The most important thing when you are dealing with lawnmower blades is safety. Never reach under your mower deck while the machine is on. Also, ensure that you remove the sparkplugs (or disconnect the sparkplug leads) to eliminate the risk of the mower turning on while you’re under there.

Step 1: Access The Blade

The first step is to remove the blade. To access the underside of a walk-behind mower, you must tip it onto its side. Ensure that you tilt the machine with the carburetor up to avoid spilling vital fluids like oil.

If you have a riding mower, you should use a hydraulic jack to tilt it onto its back wheels.

You should also pay attention to the direction the blade is facing. If you fear forgetting this, you should mark the blade or take a photograph before you remove it. Many mower owners have made the mistake of reinstalling blades facing the wrong way, which is pretty annoying.

Step 2: Remove The Blade

The next step is to remove the bolt (or bolts) holding the blade in place. Use an appropriately sized socket wrench to avoid wearing out the bolts. Hold the blade in place by wedging a wooden 2×4 between the blade and the deck. In most cases, you will have to turn the bolt in a counterclockwise direction to loosen it.

Step 3: Secure And Sharpen The Mower Blade

Once the blade is removed, you can begin sharpening it. Clamp the blade in a vice with the cutting edge pointing up. Next, use a 10+ inch file to sharpen the cutting edge. Use downward strokes and follow the existing angle until the edge is as sharp as a butter knife and free of nicks. Downward strokes will help the blade retain an edge for much longer.

If you’re sharpening for routine maintenance, you probably won’t require more than 50 strokes. However, this depends on your specific mowing conditions and the extent of the dulling.

Once you’re done filing, and you’re satisfied with the sharpness, you can reinstall the blade. Don’t forget to reference your marks or photographs so you install the blade correctly.

Grinders are another way you can sharpen your mower blade; however, using a file is the easiest and safest approach. Handheld and bench grinders are certainly faster than files, but you have a very tiny margin of error with these tools as you can just as easily over-sharpen the blade and cause it to lose balance.

Using a grinder also requires you to don safety gear like goggles and gloves.

Can A Lawn Mower Blade Be Too Sharp?

If sharp blades make a lawn healthier by cleanly cutting grass blades, then shouldn’t mower blades be brought to the sharped edge possible? Can a mower blade be too sharp?

A lawn mower blade can be too sharp. An over sharp edge on a mower blade makes the edge in constant danger of chipping, dulling, and even cracking. Though sharp blades are needed in order to cut instead of tear grass blades, when edges are too thin they become more delicate.

This is why we recommend the use of thicker blades over very thin ones.

A razor-sharp edge will dull at a much quicker rate than the “butterknife” edge we described earlier. Naturally, the faster a blade goes dull, the more frequently you will have to sharpen it.

The butterknife edge is sufficient because of the speed of the blade’s rotation when the lawnmower is in operation. This gives it enough momentum to slice through blades of grass quickly and neatly.

At such high speeds, a razor-sharp blade is susceptible to nicks from hitting twigs and other light debris.

Do You Sharpen Both Sides Of A Mower Blade?

Since there are some knives and other blades that are sharpened on one side and others on both sides to bring a point, what about lawn mower blades? Are they sharpened on one side or both?

You only sharpen the edged side of a lawnmower blade. There is no need to sharpen both sides of a blade because it only rotates in one specific direction. Sharpening both sides of a mower blade will increase the chances of the blade losing its balance, which may result in unevenly mowed grass.

This also increases the vibrations of the mower which in turn shorten the life of some of the engine parts. This can lead to more frequent repairs and even replacement.

Another thing to consider is the orientation of the blade. If the blade is placed right side up, the cut should be even and smooth. If the blade is put on upside down, the lawn will look very uneven and the problem will be easily noticeable.

The Final Touches On The Best Grit For Lawn Mower Blades…

If you are wanting to use a motorized tool of some type, then you will want to use a grit that is in between 60 and 80 on the grinding wheel or attachment.

You can also use a file starting with a coarse toothed file and finish with either a medium or smoother toothed file.

Only sharpen one side of the blade and remember not to bring the edge to too sharp of a point.

Try to sharpen your mower blades once to twice per year.

There are several other articles I recommend all about mower blades on my site here…

References

https://www.familyhandyman.com/project/lawn-mower-blade-sharpening/

https://www.gardentoolexpert.com/can-lawn-mower-blades-be-too-sharp/#:~:text=In%20a%20nutshell%2C%20you%20have,ones%20to%20avoid%20frequent%20sharpening.

https://www.youtube.com/watch?v=qFusHPPmOFo&ab_channel=ThisOldHouse

Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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