How to sharpen hedge trimmers
Things You'll Need
Align the bottom and top sets of cutting teeth. Use your gloved hands to push the two sets of teeth as close to even as you can get them. Use the butt end of your hand file to align the teeth the rest of the way by wedging the file's butt end in-between the two sets of teeth and pushing them together. Use your other hand to stop the teeth from separating on the opposite side.
Set the engine of your Stihl hedge trimmer on a flat workbench with the cutting teeth hanging off of the end of the table.
Place the tip of the file into the front-most tooth and file downward, with the cutting edge. Keep the file aligned with the
cutting edge of the tooth and use smooth, consistent strokes.
Pick the file up and pull it back; do not scrape it against the tooth. Repeat the process until the cutting edge is smooth and sharp. File the front, back and flat edge of every tooth, working your way back toward the engine. File the opposite side in the same manner, using even down strokes for every cutting surface.
Turn the hedge trimmer's engine upside down and repeat the process for the underside of every tooth.
Wipe off the metal dust with the rag once you've finished sharpening the top and bottom of every tooth.
Lubricate the teeth by hand with hedge trimmer gear lubrication. Spread the lubrication carefully over the individual teeth, going slowly to prevent cutting yourself.Source: ehow.com