Short answer
Isolate the power (remove the battery, unplug, or disconnect the spark plug cap), clean the blades, use a flat or diamond file to follow the existing bevel on each cutting edge, deburr, and oil. If blades are bent, chipped or very worn, replace them or have a dealer service them.
Sharp blades cut cleanly, reduce strain on the motor and battery, and leave healthier hedges. Blunt blades chew and tear.
Is it time to sharpen?
- The trimmer pulls or jams on stems it used to cut.
- Leaves are torn rather than cut.
- You need more passes than before.
- Battery runtime has dropped for the same job.
What you need
- Heavy gloves and eye protection.
- A bench vice or clamp, or a stable bench.
- A flat file or diamond file suited to the blade tooth.
- Wire brush and cloth.
- Blade oil or lubricant.
Step by step
- Isolate the power: remove the battery, unplug the mains lead, or disconnect the spark plug cap. Do this before you touch the blade.
- Clean off resin and sap with a wire brush and solvent or blade cleaner.
- Secure the trimmer in a vice with the blade accessible.
- Follow the original bevel angle on each cutting edge and file away from the cutting edge in one direction with steady strokes; do the same number of strokes on each tooth.
- Remove burrs with a light pass of the file.
- Check the blade clearance and fastenings; do not alter the blade gap.
- Wipe, then oil the blades.
When not to sharpen yourself
- Blades are bent, cracked or missing teeth.
- The manufacturer recommends dealer sharpening.
- You are not confident working near sharp edges.
Some manufacturers advise replacement or dealer servicing instead of home sharpening, so check your manual.
Always follow your own manufacturer’s manual: procedures, fuel mixes and service intervals differ between models, and a manual overrides any general guide.