Page 497 - Cam Design Handbook

THB14 9/19/03 7:58 PM Page 485

SPECIAL CAM MECHANISMS 485

FIGURE 14.34. Cylindrical cam for intermittent motion (eight-station
indexing).

Returning to the cam-follower action, experience has shown that rapid wear due to
a large amount of sliding (spalling) is evident as the rollers withdraw from large cams.
Furthermore, the rollers tend to skew, owing to the end thrust. Short rollers are suggested
to minimize this detrimental action. Some improvement may be made by employing
conical rollers with the apex at the axis of the drum, but they are often troublesome to
install.
Another hindrance of this cam mechanism is that it is often difficult to maintain locking
under dwell conditions. A positive lock such as a wedge-shaped block that engages a pair
of rollers during the idle period, relieving the shock load from the cam, is sometimes
employed. Shock and vibration may be caused by the backlash or clearance between the
rollers and their groove.