How to Sharpen a Lawn Mower Blade

Most of our posts revolve around industrial applications and for good reason; it's what we know.  This week though I thought I would provide a little information that would apply to just about everyone - everyone that owns a lawn mower that is.  The topic of our blog this time is the many ways to sharpen a lawn mower blade.  Sure, there are probably 1,000 websites that tell you how to do this and nearly as many videos.  Most though, seem to offer only one option.  There are many ways to sharpen a lawn mower blade, or any blade for that matter.  One things we can all agree on is a sharp blade makes for a healthier lawn.

Safety first:  Always remove the spark plug wire when working on or under your lawn mower.  Moving the blade by hand could cause the mower to start.  Also, be careful when tipping or propping your mower up; the weight of the mower can cause serious damage and injury.  Safety glasses are a must when using any of the methods below.  Oh, and wear gloves.

Also, when tipping a mower on its side use caution as to not spill the gas from the filler neck or flood the carburetor.  Also if you keep the carburetor on the higher side you can avoid getting oil into it (which will cause hard starting or engine smoking).

Regardless of the method you choose make sure to clean the blade thoroughly.  A blade all gunked up with grass will act like a dull blade and require more power to do the same work.  While you have the blade off you should clean the underside of the mower.  Remove caked on grass and crud.  I like to spray the underside of the deck with Fluid Film (a rust preventative and lubricant).  Just a light coat as you don't want to make an oily mess for grass to stick to.

Examine the blade.  A worn out or bent blade rarely benefits from a good sharpening.  The blade at left is pretty bad but can probably be saved.  A really bad blade might be difficult to sharpen with a file but a grinder would do the trick.






The oldest, and probably most popular method to sharpen a lawn mower blade is with a file.  I prefer a "mill bastard" file, one that is 10-12" long.  A mill bastard is a type of file and there are many types to choose from.  Nearly all (metal files) will work, some just cut faster and leave a better finish than others.  Remember also that files do get dull; a new file will cut much faster than a worn out file.  If your father, or grandfather, passed down a file you may want to look at replacing it.  The handle may be reusable though.

Sharpening with a file does require removing the blade; or at least it is a lot easier this way.  Mark the blade so you know which side is "down" when you remove it.  An upside down blade is worse than a dull one.  Clamp the blade in a sturdy vise; the proper use of a file requires some force to be applied.  Follow the original angle on the blade removing dull, rounded, and banged up areas. A lawn mower blade does not have to be razor sharp; in fact it will dull faster if the edge is too thin.  Shop for files and file handles.

The second method I like to use requires a 4-1/2" electric grinder and an abrasive flap wheel.  The advent of cordless grinders makes this task all that much easier.  I have even been known to put a quick sharpen on a blade without removing it.  Use a finer grit like 120 as it is less likely to gouge the blade than say 60, or 36.  (Course discs will remove material very fast).  Use light pressure and let the disc do the work.  Again, a razor sharp edge is unnecessary.


The last method requires a pedestal grinder.  If you own a pedestal grinder you probably already know how to sharpen a lawn mower blade.  The principal is the same as above.  Remember not to use heavy pressure and overheat the blade.

I know people use multi-tools and Dremels too.  The theory is the same for any method, put a new sharper edge on the blade - your lawn will thank you for it.

If you have a favorite let us know in the comment section.

Sources / images:
http://www.familyhandyman.com/automotive/lawn-mower-repair/lawn-mower-blade-sharpening/view-all
https://www.icreatables.com/yard-and-garden/lawn-mower-blade-sharpen.html
http://www.oneprojectcloser.com/sharpen-lawn-mower-blade-grinder-craftsman-murray/