Page 36 - Gear Technology Solutions

If there is a severe wear step between flanks and root fillet transitions on the
member which is not replaced, then the likelihood of an interference problem
still exists. A severe wear step as shown in Figure 2 can be detected visually
or with a drawing pin.

Figure 2: Wear step in the root of a used gear member

To account for a severe wear step in the root of the undamaged member, the
replacement gear has to be topland chamfered in order to prevent interfer-
ences between the topland corner of the replacement part and the wear step
between flank and root on the teeth of the new member. Topland chamfering is
not a widely used standard practice for the case of single member replace-
ments. The consequence of not applying the service backlash and the topland
chamfering is in many cases a repeated failure of the unit in question and a
costly repeated repair. Topland chamfers as shown on a pinion (left) and a
gear (right) in Figure 3 should only have a width of 10% of the whole depth of
the teeth and an angle which is about 30° to the flank profile at the tip of the
teeth. Curved tip roundings are even better than straight chamfers and are
recommended if the provision of machining these is available. Rounded top-
land corners have advantages over straight chamfers in case of replacing
damaged and worn gears.

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