Proper sharpening technique with the angle grinder
1 of 4Photo 1: Safety precautions before starting
Pull the wire
from the spark
plug. Remove the
gas cap, put a piece
of plastic over the
opening and replace
the cap. This will
help prevent gas
spills when you flip
the mower to
access the blade.
2 of 4Photo 2: Remove the blade
Clamp a block to the lawn mower
skirt to stop the blade from spinning
while you unscrew the nut. Use the longest
wrench you can find to loosen the nut. It’s
likely to be very tight.
3 of 4Photo 3: Make light passes
Grind the blade carefully with an angle grinder to remove nicks and dents and
restore the edge. Make several light passes to avoid overheating the blade.
4 of 4Photo 4: Balance the blade
Balance the blade on a nail after you’ve sharpened both edges. If one side is heavy,
it’ll drop. Mark the heavy side so you’ll know which end to grind. Grind a little off the
heavy side and hang the blade on the nail again to recheck it. Repeat this process until
the blade hangs level.
You wouldn’t take care of grass that’s
too long by tearing off the end of
each blade, would you? But that’s
exactly what a dull lawn mower does,
leaving the torn grass vulnerable to sun
damage and disease. You could sharpen
your mower blade with a file (it
takes forever!), a rotary tool or a bench
grinder, but we’ll show you how to do
the job with an angle grinder. It’s fast
and easy. If you don’t own a grinder, they don’t cost much to buy and can be used for all kinds of other tasks too.
To sharpen your lawn mower blade,
you’ll need a socket or wrench to fit the blade nut. Tough nuts may call for a
breaker bar and/or a penetrating lubricant.
You’ll also need two clamps, a
block of wood and, of course, an angle
grinder with a metal grinding blade.
Start by disconnecting the spark plug
wire (Photo 1). Next, place a piece of
plastic (a sandwich bag works well)
under the gas cap to prevent gas from
leaking out of the vent hole when you
tip the mower. Tip the mower so the
side with the carburetor faces up.
Clamp a 2x4 block to the side of the
mower to keep the blade from turning
while you loosen it. Mark the “grass
side” of the blade so you don’t reinstall
it upside down. Use a socket wrench or
a breaker bar to turn the nut counter-clockwise
to loosen it (Photo 2). If it’s
stubborn, soak it with penetrating oil
for a half hour and try again.
Clamp the blade securely in a vise or
to the edge of your workbench. Prepare
for grinding by putting on your gloves,
face shield, hearing protection and a
long-sleeve shirt. Before you start
grinding, hold the grinder against the
blade and tip it up or down until the
grinding disc is aligned with the angle
on the blade. Try to maintain this angle
as you grind. Keep the grinder moving
and apply only light pressure so you
don’t overheat the blade or grind away
too much (Photo 3). If you overheat the
metal, it’ll turn dark blue or black and
become brittle. Then it won’t hold an
edge. Your goal is to remove the nicks
and dents and create an edge that’s
about as sharp as a butter knife. A
razor-sharp edge will dull quickly and
chip more easily.
Make several passes across the blade
with the grinder, checking your
progress frequently. You don’t want to
grind off more than necessary. If your
blade has a lot of nicks and gouges, try
this. Start by holding the grinder at a
right angle to the blade and grinding
the edge of the blade flat to remove the
nicks. Be careful to use light pressure
and move quickly. It’s easy to burn the
thin edge. After you’ve removed the
nicks, go back to grinding at the correct
blade angle.
If your blade has deep nicks or is
cracked, bent or worn thin, don’t
sharpen it; buy a new one. You’ll find
the best selection at stores that sell and
service lawn equipment. Take the old
blade with you to get an exact match.
If you don’t grind away the same
amount of metal from both sides, the
blade can become unbalanced. You can
buy a special blade-balancing cone or
simply hang the blade on a nail (Photo
4). Correct an unbalanced blade by
grinding a little metal from the blunt
end of the heavy side of the blade until
it balances on the nail. Make sure the
marked side is toward you when you
reinstall it and that you tighten the nut
securely.
