How to Sharpen Your Lawn Mower Blade in 7 Easy Steps

When it comes to tools, it’s often said that a blunt blade is more dangerous than a sharp one.

Keeping your mower blade sharp not only helps improve performance, it also avoids putting unnecessary stress on the machine itself. A sharp blade will help prevent clogging (which is both bad for the mower and frustrating for the user) and will help look after the grass’ health.

Why Sharpen Lawn Mower Blades?

When a mower’s blade is blunt, it will tear the grass rather than cut it cleanly. This can lead to bacteria getting into the cut, which can cause diseases and yellowing of the grass. For healthy grass, keep blades sharp. You should sharpen the blade at least twice every mowing season, or after every 25 hours of use, whichever comes first.

Before doing any kind of maintenance on a lawn mower, you need to disable the engine to avoid it accidentally starting up. If the mower is electric, this means disconnecting it from any power supply and removing all batteries. For petrol lawn mowers, you must disconnect the spark plug. 

Of course, if a blade is beyond repair, even sharpening it won’t help. If the blade is bent, or there are dents and bits missing, you should replace the blade instead of attempting to sharpen it. It’s good practise to replace the blade every two years to make sure it stays in good condition. 

If you’ve got an old machine and you don’t think it’s worth either sharpening or replacing the blade, you could check out our ultimate guide to the best lawn mowers currently on the market. Otherwise, let’s get on with finding out how to sharpen existing blades!

7 Step Guide to Sharpening Your Lawn Mower Blade

how to sharpen your lawn mower blade

1) Before you remove the blade from the lawn mower, it can help to mark the bottom of the blade to avoid reinstalling it the wrong way round when finished.

2) Loosen the central nut and carefully detach the blade. If you want to sharpen the blade without removing it, we’ve got a separate article especially for that!

3) Clean the blade with some soapy water and dry it thoroughly. If there are traces of rust on the blade, clean gently with steel wool or scotch-brite.

4) Secure the blade in a vice or clamp and begin running a file along the edge of the blade. Alternatively, you can use a drill with a grinding attachment. Follow the angle of the bevel of the blade while filing.

5) If the blade edge has suffered extensive damage, it may be easier to sharpen with a grinder. Remove any gouges from the blade by running it perpendicular to the grinder, then proceed to sharpen the blade by holding it at an angle to the grinding wheel. This process generates heat, and you will need to immerse the blade in water frequently during sharpening to keep it cool.

6) Once the blade has been sharpened, check its equilibrium by balancing it from the centre point. If it is not balanced, file some material from the heavier side (not from the honed edge) until it is offset.

7) Replace the blade, tighten firmly and then reattach the spark plug wire.

remove lawn mower blade

Routinely servicing your lawn mower and regularly examining the blade for bluntness will make it easier to sharpen. Better to catch it before it gets very blunt.  If you have any problems or doubts when it comes to sharpening the lawn mower blade, any mechanic or tool hire shop will be happy to help.

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