Sandvik Coromant Silent tools - application guide - Manual (Page 48)

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3. Turning
Edge rounding
A small edge rounding (ER) gives lower cutting forces in all
directions. This means easier cutting action and less deflection of
the tool. Ground inserts have smaller edge rounding than direct
pressed inserts, which is true also for uncoated or thin-coated
inserts.
M = Direct pressed inserts G = Ground insert, normally with
smaller ER
E = Ground insert for closer
tolerances and sharp edge