Page 193 - Gear Technology Solutions

erating gear is adjusted such that the center point of the concave flank is contact-
ing the horizontal axis of the coordinate system. The direction and length of vector
RWOB defines the length and direction of the vector EXOB which represents all
basic settings required for positioning of the cutter head. In the position of the
generating gear, the concave flank is cut and the convex side is not contacted by
the inside blades represented by RWIB.

The two sets of basic settings are calculated by considering the different radii of
RWIB and RWOB and by the direction of the radius vectors RWIB and RWOB. The
radius vector direction is defined by the spiral angle of the coupling (commonly 0°)
and by the spiral angle correction which becomes necessary if the dedendum an-
gle is unequal to zero. The set-over rotation of the generating gear only depends
on the blade spacing difference between the left and right graphics in Figure 6.
The set-over rotation does not depend on the blade distance difference because
the basic settings are reference point based.

The set-over between convex and concave flank cutting is required because of the
different basic settings required for convex and concave cutting. When changing
the basic settings, a certain stock allowance for a sufficient cleanup of the second
cut concave flanks is additionally required. If the blade spacing value WAME was
zero, then the generating gear axis set-over rotation would be equal to the slot
space angle. This scenario is academic because WAME = 0 would lead to flank
mutilation if the cutting edges cross at the blade reference point. The correct gen-
erating gear set-over rotation angle DW12Z is calculated with equation (8) by em-
ploying the blade spacing angle WAME.

The equally spaced face hobbing cutter would create tooth thicknesses and slot
widths which are equal. However, due to the spiral angle error caused by the de-
dendum angle, the flank surfaces would be incorrect. A set-over to different basic
settings would not be possible because it would increase the slot width and deliver
incorrect parts.

13.6 The Solution for Creating Length Crowning

In order to form flank lead lines with a desired length crowning between the two
coupling members, the outside blade point radius has to be increased and/or the
inside blade point radius has to be reduced. This is not possible with an equally
spaced face hobbing cutter head (negative blade distance difference) because
this will additionally increase the slot width.

In order to change the cutter blade radii to achieve length crowning and to allow
for the complex interpolating five-axes set-over between the convex and concave
flank cutting, sufficient “room” between the two finished flanks has to be available.

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