Either A. Get a sharpening guide. There are several styles available, rangin from a few bucks to hundreds of dollars. It will teach you the correct angles.
Or B. pay attention to the angles of a new chain, and attempt to recreate them on your old chain.
C. Buy a handful of loops of chain, and have your dealer or a local sharpening service fix your "rocked" chains.
Learning to file your own is very rewarding and cost effective. Saws will perform better and last longer if you keep them sharp.
NEVER USE A DULL CHAIN! The extra load on the saw, especially the clutch and drive sprocket will cause excessive wear. The fine powdery dust will clog the oiler and make it pack cooling vents and air filters. Learn to sharpen and keep them very sharp.
Good rule of thumb, if its throwing chips... It's sharp. If its slinging powdery dust shut it off.
3-5 minutes with a file between tanks of fuel is all it takes. (Unless you stick it in the dirt, or hit a nail etc.)
A lot of great info at arboristsite, unfortunately the sites been under attack from hackers and may be down.
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