Power hedge trimmers make trimming shrubs, hedges and bushes almost a breeze. When performing the same task with hand trimmers, however, it's much easier to tell when the blades need sharpening--it just gets harder and harder to cut. For that reason, it is best to closely adhere to the manufacturer's blade-sharpening recommendations or at least to sharpen the blades after every 40 hours of operation. Sharp blades make cleaner cuts and give a more professional appearance to the vegetation. Sharpening the blades on a power trimmer is easy and will save you more than the sharpening time spent in decreased trimming time.
Disable the engine of the power trimmer by unplugging it from the power cord (electric models) or by unplugging the spark plug wire (gasoline models). Place the trimmer on a flat work surface, such as a workbench, so that both blades can be easily removed. Following the manufacturer's instructions, carefully remove the blades from the trimmer. This usually involves removing the plastic housing and then loosening a couple of bolts to get full blade access.
Put on eye protection. Insert the first trimmer blade into the vice. To prevent scratches, always place a small block of soft wood (or a rag) on either side of the vice jaws before clamping down too hard on the trimmer blade.
Hold one end of the trimmer blade with a gloved hand, with the other end of the blade firmly held in the vice. Inspect the blade closely, and try to identify the factory edge or "cut" of the blade. This will be the angle that you will try to imitate. Start filing this same factory-ground angle with the medium hand file. Press firmly on the blade with the file in the same direction as the factory edge. Use full strokes, and inspect the blade again after several strokes have got easier (less resistance is felt). Once a new edge can be clearly seen (clean, fresh metal is visible), switch to the fine file, and take a few more strokes to smooth up the blade.
Don't file too long in any one spot with either hand file (medium or fine) because this will cause grooves to appear. Use the full length of the file when moving it across the blade edge, remembering to keep the file at the correct angle (factory angle). File only until you get a new clean edge on the trimmer blade for the entire length of the blade.
Repeat the filing procedure for both sides of both blades. To test the sharpness, drag a piece of paper across the fresh blade edge; it should cut the paper with very little pressure applied. When finished sharpening all four blade edges, apply a light coat of machine oil to them with a rag.
Reattach the blades to the trimmer in the same manner in which they were removed. Pay attention to the manufacturer bolt-tightening specifications available in the owner's manual because this may greatly affect blade friction and performance.
Too much pressure on the trimmer blade by the vice will bend it, so use caution.
Do not overtighten the trimmer blades or leave out any washers or spacers during reassembly. This may cause intense blade friction and shorten the life of the trimmer motor.