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Sharpening mower blades

Keep your blades sharp and efficient with our tips

When was the last time you sharpened the blades on your lawn mower? Look at the grass after you’ve mowed it. If the grass blades are ragged and torn, it’s time.

Ag Engineer Bobby Grisso at Virginia Tech University says blades really should be sharpened at least once every mowing season or they'll be shredding the turf rather than cutting it. If you hit something hard like a tree limb, you'll need to check the blades then, too.

Grisso says put on some heavy gloves, unplug the spark plug wire, and use a wrench to loosen the nut so you can take the blades off and inspect them.    

"If you see any cracks or major damage on that blade, I would recommend going ahead and just replacing the blade itself," says Grisso. "If it doesn't have that, then let's go ahead and start to think about how can I sharpen that blade."

Smooth out any nicks in the blade with a file. If they're too deep, a grinder will work better. However, Grisso cautions against getting the metal too hot while you're grinding. If you see a blue spot on the blade, this indicates you've overheated it and it won't maintain its sharpness.

It's a misconception to think you have to grind a blade to a knife's edge. Grisso says if you make the blade razor-sharp, it becomes too thin. Even grass will bend it over and the blade becomes duller even faster.

"So the trick is after you grind it down to the right angle, you then go to the front, and file it back so that you've got about a 16th of an inch thickness in that front end of the blade so if it does hit something, it's not just bending it over and making things worse," says Grisso. "It's still going to cut effectively, because you've basically smoothed it, and then that 16th of an inch edge there is what becomes the cutting surface."

When you reinstall the blades, make sure they're in the right position and balanced. Torque the screws or nuts properly so they don't work loose during operation.  

Learn more about caring for your mower:

Sharpen a power mower blade: Follow these step-by-step instructions -- complete with photographs -- for sharpening your mower blades.

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