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7.1 General grinding fundamentals
To sharpen the cutting edge which has become blunt, the metal must be removed from the knife.
To do so, grind the knife up to the cutting edge until a small burr appears. Carefully remove the
burr with the finned brush by applying moderate pressure. To do so, the knife is guided approx.
6 – 10 times over the finned brush, alternating between left and right (left – right – left – right –
left).
As it is not only the sharp cutting edges, but also the long service lives that define a blade, the
cutting edge angle is another important indicator of a blade's performance.
The smaller the cutting edge angle, the higher its theoretical service life. In practice, however, it
seems that a cutting edge angle that is too small results in the cutting edge breaking off and thus
becoming blunt.
The cutting edge angle is therefore between 25° and 35°. For cutting edge angles below 15°,
the cutting edge is so unstable that it snaps with the smallest resistance.
For a cutting edge angle of more than 40°, the cutting edge is stable but it loses sharpness very
fast.
The cutting edge profile is an additional criterion for the characteristics of the cutting edge.
There are three different ground surfaces:
Convex ground surface
Tapered ground surface Concave ground surface
Convex ground surfaces are usually found on cutter knives and hand knives, tapered and concave
ground surfaces mainly on circular knives.
In essence: The profile and cutting edge angle stipulated by the manufacturer must be main-
tained.
7. Operation