Sharpen Your Lawn Mower Blade
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If there's one good thing you can do for your lawn that does not involve fertilizer or water, it would be sharpening your mower's blade. A sharp blade not only leaves a nicer looking cut surface but it also delivers a cleaner and healthier cut.
This is turf care 101. When grass is mowed, it's beeen stressed. You've just walked or driven all over it and you've cut a significant portion from its length, and in the process reduced the amount of sunlight each leaf of grass can gather to produce chlorophyll. If the cut is ragged, the grass loses excessive moisture through its cut end and it is slower to heal. Also, a ragged end turns brown and looks unattractive. More significant than aesthetics is that the the increased stress created by mowing with a dull blade makes it more likely that the lawn will be vulnerable to fungi and lawn diseases.
On the other hand, cutting grass with a sharp blade is one of the best things you can do to help your lawn withstand the stress from mowing. Mowing with a sharp blade helps it bounce back from the cut–and thrive.
Sharpen the blade of your lawnmower at least once a year. At the minimum, do this at the start of the cutting season. Mower manufacturers and turf experts at cooperative extension services vary in their opinion on what is the optimal number of hours of mowing before you sharpen. You'll see a common number of 20 to 25 hours published all over the web. That's nonsense. The truth is, there is no set number of hours. Only experience with your lawn can tell you what the optimal number of hours is. Coarse and dense southern species of grass require that the blade be sharpened more frequently (anywhere from eight to 12 hours wouldn't be surprising); where a blade that cuts northern grass species may go longer between sharpenings, particularly if the grass is healthy and moist. The more debris on your lawn (conifer seed cones, twigs, acorns and pine needles, to name a few) the more often you will need to sharpen, since the blade hits these materials and is dulled. And this is to say nothing of what happens when mowing is turned over to a teenager who may mow over anything in sight in his or her rush to get the job done.
There are a few different ways to sharpen lawnmower blades, including using a bench grinder, file, rotary tool, angle grinde, or a cordless drill with a specialized sharpening stone chucked into it.
Regardless of the method you use, there is one fundamental fact of blade sharpening: the blade must balance when you're done. A sharp blade that is out of balance, can be noisy, create premature wear on a mower and its engine, and in the worst case, even be dangerous to operate.
So let's get started.
Seven Steps to Sharper Blades
1. Disconnect the ignition wire from the spark plug. (If it’s a cordless mower, remove the battery pack.) This eliminates any chance of the engine (or motor) accidentally starting while you’re working on the mower. To avoid spilling fuel from a gas engine mower, drain its tank before beginning work.
2. Tip the mower onto its side to expose the blade mounting bolt. To ensure the bolt is as easy to remove as possible, apply a lubricant such as WD-40 penetrant. Wait 10 minutes before atttempting to loosen the bolt.
To keep the blade from turning, wedge a short wood block between the end of the blade and inside surface of the mowing deck. You can also block the blade from turning using a short length of 4 x 4 lumber.
3. After removing the bolt, pull off the mower blade, making note of which side of the blade faces downward. It’s important that the blade gets bolted back on in the same orientation.
4. With the blade removed, take a minute and scrape clean the underside of the mowing deck with a narrow-blade putty knife. Remove all caked-on grass, mud, leaves and other debris. Also, clean both sides of the lawnmower blade by first spraying with penetrating oil, and then scrubbing with a stiff-bristle brush.
5. Next, clamp the blade in a bench vise and use a drill-powered blade sharpener, grinder and a 60-grit flap disk or simply a file .
6. Once both cutting edges have been sharpened, there’s one more important step: balance the blade. You may find that you've removed more metal from one end of the blade than the other, resulting in an unbalanced blade. For blades that need a severe amount of grinding, you have to proceed in stages. Grind the blade and check it for balance, grind some more to correct a misbalance.
There are several ways to check a blade for balance. You can clamp a bolt, awl or screwdriver in a vise and hang the blade on that. You can drive a nail into a wall stud and hang the blade on that. Both methods work. If the blade hangs level, it's been evenly ground.
While the low-tech methods referenced above work, for more precise results, use a lawnmower blade balancer, a multi-tiered, cone-shaped metal fixture. Place the balancer on a flat surface, then set the blade on top; the pointed, stepped designed accepts blades with various diameter center holes. If the balance is balanced, it will remain level. If not, it will tilt to one side or the other, indicating which end is heavy and needs additional grinding.
7. Before you place the blade back onto the mower, clean out the hole for the mounting bolt.
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