Lawn Mower Blades: How to Sharpen Them and Other Things to Know

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When my husband and I bought our first home, it wasn’t the home maintenance that shocked us. We were shocked with how much time, effort and money it took to keep our lawn looking beautiful and pristine. We hoped that purchasing a brand new lawn mower would cut back on the time it took to cut the lawn. It did help, for a little while. What we didn’t know, was that we didn’t need to buy a new lawn mower to get a cleaner cut. We only needed to sharpen the lawn mower blades, to get the same results. Sharpening lawn mower blades may sound tedious, but the results are well worth the extra effort. The process of sharpening lawn mower blades is simple and straightforward and can be completed from start to finish in under ten minutes. Let’s get started!

Why Do I Need to Sharpen Lawn Mower Blades?

If you are like my me and my husband, you may have been shocked to learn you need to sharpen your lawn mower blades. A lawn mower is no different than any other tool. Over time the lawn mower blades will dull. When lawn mower blades are dull, they rip and tear at the grass instead of cleanly cutting through. This can leave the grass susceptible to fungal growth or other diseases. Freshly sharpened lawn mower blades deliver clean cuts to the grass. Which in turn allow the grass to heal faster, promoting thicker and greener grass. Not to mention that regularly sharpening your lawn mower blades also helps make it easy to push a lawn mower.

How Often Do Lawn Mower Blades Need to Be Sharpened?

There is no “one size fits all” answer to this question. A good rule of thumb is to sharpen your lawn mower blades after 25 hours of use. For most homeowners this translates to sharpening the blades about once or twice a cutting season. However, if you are mowing multiple properties, or mowing a large property, you should adjust how often you sharpen accordingly. Many professional landscapers find themselves sharpening their blades at least weekly. If you don’t know how long it takes you to mow your lawn each week you can set a stopwatch on your smartphone next time you set out to mow your lawn. That will make it easier to calculate how many weeks you can work between sharpening sessions. Set a reminder on your phone or mark your calendar to remind yourself when it is time to sharpen those blades again!

Basic Steps to Follow

While each lawn may differ slightly, the basic steps to sharpen lawn mower blades should be about the same. 

Step 1- Safety Precautions

It is a good idea to take a few safety precautions anytime you plan on working with sharp blades. You should remove the spark plugs from your lawn mower anytime you plan on working around the blades. This helps to eliminate the risk of the the piston accidentally firing and sending the blades spinning while you are working. The last thing you need is a trip to the emergency room with severed fingers or a broken hand. You should also tip the lawn mower to its side with the carburetor side up. This stops oil from leaking and causing smoke clouds to emit the next time it is in use.  Placing a tarp under your lawn mower will catch any leaking oil and stop it from staining your garage floor.

Step 2- Remove the Blades

Grab a thick pair of work gloves any time you work with the blades so that you can avoid unnecessary cuts on your hands. You will find most blades are attached by a single bolt. A little tip to stop the blade from moving while you are removing it from the lawn mower is to use a 2×4 block to stop it. Wedge the 2×4 between the blade and the deck of the mower so it is secure. This 2×4 trick stops the temptation many have of using their feet to keep the blade still. Next, use a long handled wrench to loosen the bolt and remove the blade. If the bolt is on too tight, put a little WD-40 on the bolt and let it sit for a minute before trying again. Once the blade is removed, place the lawn mower back on all four wheels.

Step 3- Sharpen the Blades

There are a few ways you can sharpen your lawn mower blades. The easiest is to use a file called a mill bastard file. Clamp the blade into a vise and use the file to sharpen the blade. Lawn mower blades are made of soft steel so it usually only takes around 50 strokes before the blade is sufficiently sharp. Avoid over sharpening the blade, which will actually cause the blade to dull more quickly. If you choose not to use a file, you can use a grinder. A grinder will sharpen your lawn mower blades much quicker than a file. The downside is that it is easy to overheat and ruin your blade. If you do not feel comfortable sharpening your lawn mower blades you could always bring the blades into a shop to have it professionally sharpened with a grinder.

Step 4- Replace the Blade If Necessary

When removing your lawn mower blades you may find that there are big chips in the blade, or that the cutting edge has thinned down. If that is the case it may be time to replace the blade. Bring the old blade into the hardware store so you can find a matching replacement. Resist the urge to “upgrade” to a mulching blade. A mulching blade cuts and spins differently than a traditional blade and is often not compatible with traditional push lawn mowers.

Step 5- Reinstall the Blade

After you have either sharpened or replaced the lawn mower blade it is time to reinstall. First you should double check the the blade is still balanced. Hang the blade from a nail and make sure it still lays horizontal. If it dips down to one side it is not even and will need to be sharpened and adjusted until it evens out. Then replace the blade and the bolt and tighten as much as you can. Replace the 2×4 block and tighten the bolt even further. If a blade is not balanced or is too loose it can throw off the engines timing. This can make your mower difficult to start. Double check the the blade is installed the correct way. Some handymen become frustrated after they sharpen a blade and find the grass still won’t cut. Only to find out that they reinstalled the blade backwards.

In Conclusion

Sharpening your lawn mower blades is a forgotten chore that can make a huge difference in the health and beauty of your lawn. Following these few simple steps can bring you one step closer to the yard you’ve always dreamed about. Ten minutes, twice a season is all it takes. So, what are you waiting for?

Related Article: Best Electric Lawn Mower – Our 10 Best and Top Pick

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