Having your power tools in good working order isn't just a convenience thing -- it can also help keep you safe. When your gas or electric-powered hedge trimmer starts to cut less efficiently or the machine starts to snag on hedge branches, it's time to sharpen the blades. With a basic mill file, this job will take less than an hour.
Put on your leather gloves to protect your hands as you work with your blades. They might not be as sharp as you want them to be just yet, but they can still cut you.
Set your hedge trimmer on a flat surface, such as a table.
Pull out the spark plug wire to disconnect the spark plug. The spark plug is round and tubular with a thick wire attached to one end. Removing it will ensure the hedge trimmer doesn't start up while you're sharpening. If you have an electric model, skip this step -- but make sure your hedge trimmer is unplugged throughout this process.
Use your pointer finger and thumb to squeeze the upper and lower blades of your hedge trimmer together, so that the teeth of the upper blade rest over top of the teeth of the lower blade. If the teeth are not perfectly aligned after that task, place the head of a screwdriver between two of the teeth and press the head toward one set of teeth, suggests eReplacementParts.com. The screwdriver head acts as a pry bar that can help align the teeth perfectly.
Set your mill file against the tip of one of the teeth of the blade, lining the file up at the same angle as the angle on the blade. Each tooth has a cutting edge on its tip as well as on its two sides, and you'll need to sharpen all three edges. Start with one edge and slide your file downward toward the blade edge, going with the angle of the blade. Files will only sharpen when you're moving forward.
Lift the file off the blade after you've reached the edge, and then start again, sharpening in a downward direction until you reach the edge of the blade. As you do this, you'll probably notice that portion of blade starting to look shiny; that's how you know you're sharpening it.
Move your file to one of the side edges of the same tooth, once again lining your file up so that it rests with the angle of the blade. Move your file in a downward direction, toward the edge of the blade several times, or until you see that the blade is shiny.
Sharpen all three sides of each blade on the top of the trimmer, and then flip the trimmer over and sharpen all three sides of each blade on the bottom of the trimmer.
Wipe down the blades with a wet rag once you're done filing.
Squeeze a small amount of lubricating oil onto the teeth, or use a product recommended by the hedge trimmer's manufacturer to lubricate the teeth after sharpening.
Replace the spark plug wire.