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Figure 12: 3-face ground blade with cutting edge hook angle definition
22.5 Influence of some Angles on the Cutting Process
Observation of cutting edges with said side view in Figure 13 shows the three
principle possibilities of a positive Cutting Edge Hook Angle (left), a neutral,
zero degree Cutting Edge Hook Angle (center) and a Negative Cutting
Edge Hook Angle (right). Positive cutting-edge hook angle of 2° to 4° are de-
sirable. Often this is not possible to achieve, however, zero degree is still an
acceptable value. Negative cutting-edge hook angles have to be avoided be-
cause the sheared off chips will flow towards the blade tip. This will negatively
influence the surface finish and increase chip force and temperature at the
blade tip region. The result might be a top fracture of the blade, called “Banana
Peel” as shown in the photograph in Figure 14.
Figure 13: The three principally different cutting-edge hook angles
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