Page 316 - Gear Technology Solutions

Figure 11: Blade angles and blade nomenclature, left 2-face-,
right 3-face-ground

An interesting and often neglected phenomenon is the Cutting Edge Hook
Angle. To understand this very important angle, the graphic of a two-face
ground blade, left in Figure 12 is employed. The graphic shows a permanent
front face which is oriented to a certain side rake angle, but the blade hook an-
gle is zero like in all blades with a permanent front face (see also Figure 10).
The blade hook angle is zero as long as no pressure angle is ground onto the
blade stick. Grinding the pressure angle forms the red surrounded surface in
the right graphic in Figure 12. A view perpendicular to the left side wall of the
blade shank will show an angle between the red dashed line (projection of the
cutting edge to the side wall) and the original corner of the blade stick. This is
the Cutting Edge Hook Reduction Angle. If this blade is mounted in its cutter
head slot, then the blade is inclined by the blade slot tilt angle. In this position,
a view perpendicular to the side wall of the blade, which is mounted in its cut-
ter head slot will show a cutting edge, which is inclined under a certain angle to
the direction of the cutting plane (Figure 1). In case the cutting plane is orient-
ed perpendicular to the face of the cutter, then the cutting-edge hook angle is
calculated:

Cutting Edge Hook Angle = Blade Slot Tilt Angle – Cutting Edge Hook
Reduction Angle

Slightly simplified, this means, looking at a blade sideways after it is mounted
in the cutter head shows the observer the cutting-edge hook angle. It is not
possible to get a similar concrete vision of the top rake angle.

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