Page 81 - Gear Technology Solutions

cause the pinion topland corner will not mesh below the green line. In both cases
of lost area, either the edge radius of the blades is too large, or kinematic undercut
or physical undercut exists.

Figure 12: Lost working areas drawn in gear tooth projection

A distinction between physical undercut, kinematic undercut or interference due to
a too large blade edge radius is difficult in the design stage. The graphics in Fig-
ure 13 propose a procedure which reveals the reason for a lost dedendum (root)
area. If the edge radius is too large, then it limits the working depth (case 1). When
the edge radius in the calculation is changed to a small value, for example 0.1mm
and the lost area in Figure 12 stays the same, then kinematic undercut exists
(case 2). If the end of the working depth drops down and matches the end of the
gear root fillet in Figure 12, then the blade edge radius was too large, or the clear-
ance is too small (case 3). An increase of the lost area after reducing the edge
radius reveals a physical undercut (case 4) [2]

Figure 13: Lost working area

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