Echo HCAS-235ES-LW Operator's Manual page 29

Care for cutting blades
Wear gloves to protect hands from sharp blades.
If you experience any problems with sharpening the blade, we recommend that you take it to your dealer.
Failure to observe these precautions could lead to injury.
1. Bolt slots
Maintenance and care
CAUTION
Lubricating blades (Every 4 hours of operation)
Apply a few drops of oil the each bolt slots at the bottom of
blades.
Sharpening blades (As needed)
NOTE
Use a disk grinder or smooth flat file.
1. Remove all nuts and bolts securing cutters to frame bar.
2. Remove cutters.
3. Hold a cutter in a vice.
4. File and reshape the cutter edges as shown.
5. If frame bar is deformed or damaged, replace with new one.
(A):10 mm radius
(B):100° (Approx.)
(C):35°
(D):45°
(E):Blunt extension
Do not sharpen the blunt extension at the tip of the cutter.
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CAUTION