Push lawn mowers cut yards in a fraction of the time of the old manual rotary mowers ever did but due to the high speed at which the blade turns, keeping the blade sharp is a necessity. Dull blades can tear, rather than slice, grass and the torn edges both detract from the look of your lawn as well as expose it to disease. Most blades can be sharpened in less than an hour and it is something you only need to do a couple of times a year.
Remove the Blade
Tilt the mower slightly to one side--away from the gas cap. Don't tilt it too far or gasoline may spill out of the engine.
Secure the blade with one hand and loosen the bolt that holds the blade in place with the other hand using a wrench or socket.
Remove the blade from the mower shaft and replace the mower on all four wheels.
Sharpen the Blade
Clamp the blade to a bench, table or stair tread. Rather than clamping it in the middle, position the clamp behind one of the cutting surfaces. The cutting surface should protrude past the edge of the clamping surface.
Start at the end of the cutting surface closest to the center of the blade by placing the tip of the file on the end of the cutting surface and push the file away from the center while also pushing the file up. Repeat the process until you reach the end of the blade.
Flip the blade over and sharpen the back side of the same cutting surface.
Spin the blade and sharpen the other cutting surface in the same manner.
Replace the blade on the push lawn mower.