Page 88 - Gear Technology Solutions

6.5 Why the created Undercut is Required for a correct Meshing?

During the meshing process with the mating member, the top corner, as shown
in Figure 5, requires the room the undercut provides in order to roll without
any interference through the entire mesh. Although the opposite flank of the
red tooth in Figure 5 (left flank) is already in contact with the flank of the
preceding tooth of the undercut pinion, the room the undercut provides in the
circled area is required to avoid a collision.

Figure 5: Interaction of undercut tooth with the mating tooth

The reason why the kinematic interaction between the two members is always
as shown in Figure 5 is the fact that both members are generated with the
same virtual generating rack. The generating rack is “only” virtual, but the hob
cutter in Figure 3 represents the generating rack from the back in order to
generate the pinion teeth, and another hob cutter (not shown in Figure 3) is
positioned at the front of the generating rack to generate the mating gear. In
other words, the virtual generating rack becomes a physical reality which
provides the kinematic coupling which is necessary for an undisturbed
meshing and the correct motion transmission between pinion and gear.

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