This guide explains how to sharpen a lawn mower blade and how to keep mower blades sharp, which is essential to proper lawn care.
Without an adequately sharp mower blade, it’ll be very challenging to get a clean cut when mowing your grass.
As summarized on Reddit, you can find my step-by-step instructions for sharpening a mower blade. You can choose from several methods to find the one that suits you the best.
Whether you’re simply trying to sharpen mower blades with a file, a grinder, or a specialized tool, this is a straightforward DIY mower project that can save you between $50-100 in lawnmower repair costs – each time you do it yourself.
By the end of this guide, you will be equipped to handle this DIY job easily.
How To Sharpen a Lawn Mower Blade:
Step 1: Remove the Lawn Mower Blade
(As a safety precaution – Remove the spark plug first before removing the mower blade).
Removing the blade from the mower – is a simple matter of loosening the single bolt that holds it to the crankshaft. This bolt will usually be quite tight, but you’ll find that it’s possible to remove it with a sturdy wrench or socket.
Note: If the mower blade wants to “turn” in the same direction while you’re loosening the blade nut, grab a short piece of wood (like a chunk of 2×4)and wedge it between the mower blade and the mower firmly – so the blade cannot rotate.
QUICK TIP: To make sure you reinstall the mower blade back on the mower – with the correct orientation, it is a good idea to use a spritz of spray paint to mark the bottom of the lawnmower blade.
When you reinstall the blade, place the marked side toward the ground. That sounds like common sense – But an upside-down blade won’t do you any good 🙂
Step 2: “Clean and Inspect” the Lawn Mower Blade
Knowing how to sharpen lawn mower blades is good, but it won’t help much if your blade is beyond salvaging. Once the blade is off, thoroughly remove grass debris with a stiff brush and inspect it visually.
Now, look for any significant nicks or severe damage to the blade caused by rocks, roots, or other obstructions. If you see any severe damage, you’re likely better off buying a new mower blade instead of trying to get the old one back into usable condition.
Step 3: “Sharpen” Lawn Mower Blade
Next comes the actual sharpening – of which there are three (3) different methods to choose from. You can use a Hand file, Power Drill Wheel, or Bench Grinder.
Each mower blade sharpening method is described below.
Hand File Method:
The first method is to apply a hand file to the blade’s edge. Because mower blades are manufactured from softer steel grades, a file or a “Manual” mower blade sharpening tool can give a sharp edge.
To do this, use a hand file to sharpen the blade – start from the top side and work downward toward the cutting edge. Sharpening the blade in this direction – will ensure a sharp, even blade that will hold its edge reasonably well.
Of course, when using a manual mower blade sharpening tool, you use the self-guided tool instead of a hand file, and it delivers the properly filed edge for you.
Power Drill “Wheel” Method:
Another option is to use a powered grinder wheel to sharpen the blade. The grinder wheel attaches to a Power Drill, and although it offers less control than a hand file, it provides quicker results.
If you’re pretty handy with a wheel grinder, you’ll probably be able to manage it without too much trouble.
Note: You don’t have to remove the blade with the power drill grinder. With this step, however, if you do not remove the blade from the mower, you cannot “balance the lawnmower blade” when finished.
Many people find this the fastest and best way to sharpen lawn mower blades, and you can easily pick up a power drill sharpener at any hardware store.
Bench Grinder Method:
The final method for sharpening your mower blade is for the “Die-Hard” DIY people! That is – With the bench grinder approach.
You use a bench grinder instead of a hand file or power drill grinder to hone the mower blade.
This is an advanced expertise approach, but if you’re good with a bench grinder, it is a surefire way to quickly get a sharp mower blade edge.
Step 4: “Balancing a Lawn Mower Blade
Before putting the blade back on your mower, you should check to be sure it is still correctly balanced. The metal removed during sharpening can cause the blade to fall out of balance, translating into poor and uneven cutting.
To check the balance, you should consider getting a blade balancing tool, which is very economical. It is a small conical tool on which the blade sits to check the balance of the mower blade.
If the now filed-mower blade remains balanced on the blade balancer cone, it will be reinstalled. If it tilts to one side, slowly remove a little metal from the heavy side until it regains proper balance.
Step 5: Re-Installing a Lawn Mower Blade
Now that your blade has been sharpened and balanced, you can return it to the mower. To do so, firmly tighten down the bolt that previously held it onto the crankshaft. You can replace the spark plug with the blade reattached, and you’ll be ready to mow again.
How to Sharpen a “Mulching” Lawn Mower Blade
Note: In case you’re not sure if you have a Mulching or Regular mower blade – The photo below will show you the noticeable differences:
Many lawnmowers are manufactured with Mulching blades that make it easier for grass clippings to be returned to the soil and break down into usable nutrients for live grass over time.
The unique twin-blade profile can be identified in the mulching blades (Photo Above).
The basic process of removing, cleaning, and sharpening mulching blade varieties is essentially the same as for a regular mower blade. The only significant difference comes in sharpening the curved portion of the blade that lifts the grass for mulching.
To sharpen a mulching blade, you’ll begin with the same basic technique as before, using a file or grinder to work down the beveled portion of the cutting surface from the top.
However, switching to a smaller file is best when you reach the curved portion of the blade. Using a smaller file will allow you to properly hone the cutting edge on the curved surface, ensuring you get the best possible results from your newly sharpened blade.
As before, you’ll want to balance the blade before reinstalling it and then place it back on the mower.
Sharpening mulching blades is a project that can take some practice to master, so don’t be too discouraged if you don’t get it perfect the first time.
After a few sharpenings, you can quickly and efficiently hone the cutting edge of any mulching blade.
Time To Look At A New Mower? Check out our review for the Best Self-Propelled Gas LawnMowers you can buy.
Frequently Asked Questions (FAQ)
Q: How Often Should You Sharpen a Lawn Mower Blade?
A: As a general rule of thumb, you should sharpen your mower blade after every 25 hours of use. So, for example, if your yard takes an hour to mow, you would sharpen your knife after every 25 mowings, or in most cases – once per season.
According to Home Depot, another good measuring tool is to look at your grass blades after mowing. If they look brown and frayed instead of green and clean-cut, it may be time to sharpen your mower blade.
For houses with small yards or those that only mow once a week, sharpening the blade at the beginning of every season is more practical as part of routine mower maintenance.
However, If your yard is large or you mow multiple times a week – a few more sharpenings throughout the season may be in order.
Q: Do New Lawn Mower Blades Need to Be Sharpened?
A: New lawnmowers include pre-sharpened mower blades, allowing you to use your mower immediately.
If you mow and suspect the blade came with a dull blade, you can consider returning the mower or asking them to provide you with a sharp one at no cost.
Q: How Important Is Mower Blade Balancing?
A: If you’re going to sharpen the mower blade, you should be sure it’s balanced each time you finish sharpening it.
An unbalanced blade can affect the quality of your cut and, in extreme cases, could damage your mower’s crankshaft.
Q: Do Electric Mower Blades Need to Be Sharpened?
A: Regardless of the “power source,” all Lawnmower blades experience wear and tear that dull their edges over time, and therefore, all mower blades need to be sharpened at least once per season.
Q: Does Mower Blade Sharpness Affect How Your Grass Looks?
A: A sharp mower blade can distinguish between a green, evenly trimmed lawn and a dull or brown-tipped, uneven grass length.
A dull blade—the lawnmower will actually “tear” the blades of grass as it cuts them, resulting in a brown tip appearance.
With a sharp blade – you avoid this problem by actually “shearing” the blades of grass off while cutting them.
Conclusion
Now that you know how to sharpen a lawnmower blade, you’ll be able to improve the appearance of your yard while saving money on costly trips to a lawnmower repair service company.
Remember that all lawn mower blades eventually wear out. Occasionally, you’ll need to replace the old blade rather than sharpen it.
In most cases, a quick sharpening will let you make an old blade look new again, and at the same time – your lawnmower will work that much more efficiently – and your lawn will look amazing!
