A Midsummer's Sharpening: How to Sharpen Your Lawn Mower Blade

For a more effective cut, keep your lawn mower blade sharp!

| July 24, 2008

lawn mower

The sharpness of a lawn mower blade affects performance of the machine and appearance of the lawn.


Sharpening your lawn mower blade is part of routine maintenance. It’s less complicated than you might think, and you’ll only need a few simple tools. If the tips of grass look ragged and brown after you mow, the problem may be a dull mower blade. Instead of being neatly cut, the grass is beaten to pieces.

Before you begin this project, think about safety. Just like when you pull the starting cord, moving the blade turns the engine, which could start. Disconnect the wire from the spark plug to avoid an unintentional start. It’s a good idea to wear leather gloves when removing the blade, but don’t try to hold the blade with one hand while working a wrench with the other. Instead, wedge the blade against a 2-by-4 to prevent it from turning while you remove the nut that keeps it in place. Before you start sharpening the blade, clamp it securely in a vice.

Choose the Right Tool

There are several tools you can use for sharpening the blade: a file, a bench grinder or a hand-held grinder. Electric grinders are available at most hardware stores for under $70. They will likely remove too much blade quickly, and they usually grind a concave edge, which will become dull sooner and is weaker than a V-shaped edge. The heat produced by a rapidly turning grinder can also weaken the blade. If you choose to use a grinder, dip the blade in water frequently during the sharpening process, and dry it each time before proceeding. This will cool the metal to reduce overheating and weakening.

A coarse-toothed file is probably the best choice. You can find one for under $10 usually. They’re easy to use, especially if you’re uncomfortable with power tools. Run the file toward the sharp edge of the blade. It removes material as you push it (not when you pull it back). Lift the file after each stroke; don’t “saw” with it. Follow the same angle as you see on the blade, and don’t sharpen the flat side. But you should run the file lightly over the flat side to remove the “burr” that forms as you sharpen.

Keep Your Balance

Try to take an equal amount from both ends of the blade to keep it in balance. If it’s not balanced, it will make the mower vibrate. To check for balance, hang the blade on a nail in the wall or from a screwdriver to see if one end is heavier than the other. You also can use a blade balancer, which is a small cone-shaped tool designed just for this purpose. If the blade isn’t balanced, file or grind the end of the side that is too heavy.

When you attach the blade, the wings at the ends of the blade should be up toward the deck (not toward the ground). These lift the grass clippings so they’re chopped as you mow. If the blade is upside-down, the sharp edge won’t lead as the blade turns.

bill eckert
8/25/2011 5:16:52 PM

The initial warning about the spark plug wire is technically correct and TERRIBLY WRONG!!! that wire has been in the same position for X number of years and when removed will move right back where it "belongs"....before you EVER go under a rotary mower REMOVE THE SPARK PLUG and PUT IT IN YOUR POCKET!!! (USN Safety Weenie, Retired!)

frank mulcahy
6/23/2009 4:08:36 PM

SAFETY. make sure the plug lead is removed. There have been lots of accidents occur with accidental start while removing entangled rope from the cutting disc, same with blade removal. Be careful with this.

6/19/2009 3:38:50 PM

Great writing on the sharpening process. I applaud all efforts to get people to keep their tools sharp. I'm a maniacal honer and you can see my stuff at www.theperfectedge.com. The lawnmower blades here in New England are especially tough to keep sharp due to all the rocks in the soil. They come up every year from the frost.

b knight
6/18/2009 12:20:16 PM

Good video of sharpening technique. Need to address "cordless electric" mowers as well as the old gas fired beasts. Hopefully we have more people switching over to electric everyday..... Bruce.

dick holland
6/18/2009 7:12:02 AM

I installed 2 of the "yellow" self-sharpening blades on my riding mower recently. Rather expensive, around $90 for the pair. Sounded great not having to sharpen, but then started wondering while installing. If I can cut them to size with a sharp object and the amount of "give" to the blades when I was tightening them to the deck, how will they really hold up? I never could find anyone who rated the blades before I bought them, which made me put off buying for a couple of years. My grass, mow about 4 acres each week, doesn't look any better, and in fact am getting the pulled look of a dull blade. Feeling under the deck, mower off of course, the blades do not feel sharp. Anyone else using these blades? Comments?

jim adams
6/17/2009 12:49:30 PM

I have two of the new "hardened" blades on my riding mower... which i appreciate. It takes a lot less sharpening, it holds a sharper edge longer, and the cut is more cut than tear. Blades must be balanced as they are sharpened, or you'll notice a vibration that gets worse with every home sharpening. It's simple to balance a blade --- put a short piece of 2 x 4 on your bench, table or ground w/ one of the narrow sides up. Put a round pencil on top of that. When you've sharpened both sides, put the blade on the pencil so the pencil is visible thru the middle of the bolt hole. If the blade tilts, re-grind the heavier side (the side which tilts down. Keep going till the blade stays almost level. Close is good enough. And another thing ... try to make the outer corner as square as you can. A rounded corner doesn't cut worth a darn. If that is difficult, then go thru your lawn and remove rocks, bricks, pavers, etc so there is little for your blade to dull itself against (apart from grass, that is) I use a 6" high cut which gives me just as much (or just as little) mowing as the standard golf course bur cut. However, when it gets droughty and dry, and others lawns have large brown spots ... our lawn is green and comfortable for bare feet. In general, i prefer the feel of a long-cut lawn, both to walk on and to lie around on and for the looks of it. +, we have a larger number of species --- six or seven grasses, ground ivy, a couple vetches, lots of white clover, a little red clover and a number of other. We occasionally let it grow up to give us seeds for next years lawn.

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