Working with dull trimmer blades places extra stress on gas hedge trimmers and reduces the lifetime of other important trimmer parts. Dull blades also slow down the work, requiring multiple attempts when one steady pass should do. Cuts made with dull blades often are incomplete, leaving behind ragged leaves and many clippings still partly attached to the bushes. Sharpening gas trimmer blades takes time but the results are well worth the effort.
Allow the trimmer to completely cool down before working on the blades. Find the studs holding the trimmer blades to the blade guard and remove the adjustment nuts. Remove the blades from the machine. In most trimmers one blade is fixed to the blade guard while a slot in the second blade attaches to a reciprocating cog beneath the motor. If both blades show beveled edges, both blades must be sharpened.
Clamp one of the blades in the bench vise with the cutting edges fully exposed and the bevel toward you. Place the end of the file flush against the bevel of a cutting tooth. Guide the file and apply light pressure with one hand, pressing on the part of the file that projects beyond the blade. Push forward carefully with the handle of the file firmly in the other hand.
Use the full length of the file face. Keep the same bevel angle as was established at the factory--usually 45 degrees. File until the edge shows new metal the full width of the bevel. Move the file to another tooth edge and repeat.
Finish the row of teeth secured in the vise and then release the vise jaws. Shift a new section into place, tighten the vise and repeat step three. Continue until you have filed the entire length of the blade.
Remove the burr on the back of the blade by rubbing the blade over a flat sharpening stone.
Reattach the blades to the hedge trimmer. Adjust the hedge trimmer blades with the locknuts on the blade studs so that the cutting blades move freely but without chatter. Oil the blades.