Power lawn mowers come in two types--walk behind or ride on. Walk behind mowers can be the typical push lawn mower that is so ubiquitous in the suburbs or can be the larger commercial kinds with a wide deck and multiple cutting blades. Riding mowers often have more than one blade to better cut larger areas in one pass. Sharpening the blades on the these power mowers is a simple maintenance need that can be performed in usually less than an hour and leads to better looking lawns and reduced stress on the mower engine.
Place the front wheels on jack stands to support them roughly 8 inches above the ground. Light-duty jack stands are available at most automotive stores and are lightweight and compact.
Lie on the ground to reach the middle of the lawn mower blade where it is attached to the mower shaft.
Secure the mower blade from rotating with one hand and use a wrench or socket with the other hand and unscrew the bolt holding the blade in place.
Place the blade in a bench vise. The top of the vise should be an inch or so below the cutting edge of the blade to provide maximum support.
Stand to the inside of the cutting edge and begin sharpening.
Sharpen the blade by running the file from the inside edge of blade toward the outside edge of the blade. At the same time, push the blade upward and away from the blade. You don't have to cover the length of the blade with just one stroke.
Sharpen the back side of the blade using the same process. You aren't trying to sharpen the blade to the point of being able to shave with it, but both faces of the cutting surface should form a point where they intersect and not be rounded. Once you have achieved this, stop sharpening and repeat the process on the other cutting edge on the blade.
Replace the blade on the mower, being careful not to cut yourself. Even though the blade may not be razor sharp, it is still easy to cut yourself it you run your hand along the cutting edge.