How To Sharpen A Lawn Mower Blade

No matter what type of lawnmower you own, it's important you keep that blade sharp. Otherwise, you risk yanking your lawn instead of slicing it cleanly and healthfully down to size. A sharp blade also keeps your mower running smoothly and shortens the amount of time you spend working on your lawn. The DIY experts at Stack Exchange offer a few tips on keeping your blade sharp, and doing so all by yourself.Image: Sean Gallagher.


Is it possible for a DIYer to sharpen the blade on his or her lawn mower? If so, how would I sharpen the blade on my lawn mower? It is a reasonably basic push mower but it does have a 'mulching' blade.

-- (Originally asked by Jack)

Answer: 10 Steps

1) Remove the blade by removing the nut that attaches it to the mower. 2) If there is any rust on the blade, remove it with steel wool or a steel brush. 3) Clamp the blade in a vice, or to the edge of a solid work surface. 4) Run a file down the cutting edge, following the same angle already on the blade. 5) If the blade is badly damaged, you will have to use a bench grinder or have it professionally sharpened. 6) Run the blade perpendicular to the grinding wheel to remove any nicks or gouges (this will give you a straight blunt edge). 7) Hold the blade at the proper angle (the angle already on the blade) and grind the length of the blade until it is sharp. 8) Balance the blade (from the centre point) on a nail or on a Blade Balancer (~$US5) to check that the blade is balanced. 9) If the blade is not balanced, you will have to remove a bit of the material from the heavier side (Do not remove this material from the cutting edge). 10) Now that your blade is sharpened and balanced, reattach it to the mower.

Sharpening the blade more frequently will make the task quicker and easier, since you won't have to grind as much to get a good edge.

If you do sharpen the blade using a power grinder, heat from the process can weaken the blade, so you'll want to quench the blade to prevent overheating. Dip the blade in water frequently during the sharpening process to cool it, and wipe it dry before you continue grinding.

-- Answered by Tester101

Safety Note: Remember Step 0

Make DAMN sure the lawnmower cannot start up while you are removing the blade. I have a relative who is missing a few fingers after he bump-started the motor while trying to remove the nut. Modern machines have better interlocks preventing this sort of thing, but pulling the spark plug and blocking the blade with something thick are also good precautions.

-- Answered by Alex Feinman

Answer: Keep in Mind...

If you have a workbench with a vice, sharpening a lawnmower blade is relatively easy. The other answers have already covered the basic techniques. I don't own a bench grinder, but I have used a metal file, and a cordless drill with a grinder tip. Both methods worked pretty well for me. Rarely takes me more than 15-20 min (not counting removing and re-attaching the blade).

A few comments not covered in the other answers:

- The blade should be "butter knife" sharp, not "razor blade" sharp. If you make the edge too sharp, it will curl up as it gets dinged by tiny pebbles. (A brand new blade from the factory is usually only butter knife sharp.)

- Don't change the overall angle of the blade edge while sharpening it. The manufacturer knew what it was doing when the blade was designed.

- Make sure your blade is balanced when you are done. If it is off balance, it will hurt the mower.

- The big home improvement stores sell a little "kit" for sharpening and balancing your blade that is pretty cheap. All you need is a drill and a vice.

- Some curved mulching blades are difficult to sharpen properly. It may be easier to just replace it.

- For a small mower, an OEM replacement blade can be found for $US10-$20. So, if you are struggling to sharpen your current blade, don't be afraid to buy a new one. If nothing else, having a spare blade or two around can make life easier.

Check out a few other tips on basic lawnmower maintenance.

-- Answered by msemack

Answer: The Quick Fix

Use coarse grit sandpaper to give your blade a quick sharpening. This doesn't work for big nicks and dings, but does a decent job just cleaning up the edge.

Then make sure you're mowing your lawn the right way.

-- Answered by mohlsen

Answer: Close might be Close Enough

There is certainly an optimal angle to sharpen your lawnmower blade, but close might be good enough. Use a dremel (or better yet, a dremel lawn mower sharpener attachment) or even a file.

If you keep an edge on your blade, the mower will run considerably smoother. And the quicker the cut, the less stress on your lawn.

Do you know the secret to DIY sharpening a lawn mower? Submit your answer at Stack Exchange or leave it in the comments. Stack Exchange is a place to trade expert knowledge on diverse topics from software programming to cycling to scientific scepticism... and plenty in between.


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