Echo SRM-280 - Manual (Page 26)

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sharpenIng metal blades
Three styles of metal blades are approved for use on the ECHO Brush
Cutter. The 8-tooth blade can be sharpened during normal mainte-
nance. The clearing blade and 80 tooth blade require professional
service.
Before sharpening, CLOSELY inspect blade for cracks (look at the
bottom of each tooth and the center mounting hole closely), missing
teeth and bending. If ANY of these problems are discovered, replace
the blade.
When sharpening a blade, always remove the same amount of materials
from each tooth to maintain balance. A blade that is not balanced will
cause unsafe handling due to vibration and can result in blade failure.
Tool required: Flat file (preferred). Electric grinder if special care is
used. Round (rat tail) file for gullet (radius).
1. File each tooth at a 30 degree angle a specific number of times,
eg. 4 strokes per tooth. Work your way around the blade until
all teeth are sharp.
2. DO NOT file the 'gullet' (radius) of the tooth with the flat file.
The radius must remain. A sharp corner will lead to a crack and
blade failure.
IMPORTANT
If an electric grinder is used, use care not to overheat teeth, do not
allow tips/tooth to glow red or turn blue. DO NOT place blade in
cooling water. This will change the temper of the blade and could
result in blade failure.
3. After sharpening teeth, check each tooth radius for evidence of a
square (sharp) corner. Use the round (rat tail) file to renew the
radius.