Figure 11-21.-Universal joint (Hooke type).Figure 11-22.-Ring-and-trunnion universal joint.forms. They are used in nearly all types and classes ofmachinery. An elementary universal joint, sometimescalled a Hooke joint (fig. 11-21), consists of twoU-shaped yokes fastened to the ends of the shafts to beconnected. Within these yokes is a cross-shaped part thatholds the yokes together and allows each yoke to bend,or pivot, in relation to the other. With this arrangement,one shaft can drive the other even though the anglebetween the two is as great as 25° from alignment.Figure 11-22 shows a ring-and-trunnion universaljoint. It is merely a slight modification of the old Hookejoint. Automobile drive shaft systems use two, andsometimes three, of these joints. You will read moreabout these in chapter 13 of this book.The Bendix-Weiss universal joint (fig. 11-23)provides smoother torque transmission but lessstructural strength. In this type of joint, four large ballstransmit the rotary force, with a smaller ball as a spacer.With the Hooke type universal joint, a whipping motionoccurs as the shafts rotate. The amount of whip dependson the degree of shaft misalignment. The Bendix-Weissjoint does not have this disadvantage; it transmits rotarymotion with a constant angular velocity. However, thistype of joint is both more expensive to manufacture andof less strength than the Hooke type.CAMSA cam is a rotating or sliding piece of machinery (asa wheel or a projection on a wheel). A cam transfersmotion to a roller moving against its edge or to a pin freeto move in a groove on its face. A cam may also receivemotion from such a roller or pin. Some cams do notmove at all, but cause a change of motion in thecontacting part. Cams are not ordinarily used to transmitpower in the sense that gear trains are used. They areused to modify mechanical movement, the power forwhich is furnished through other means. They maycontrol other mechanical units, or they may synchronizeor lock together two or more engaging units.Cams are of many shapes and sizes and are widelyused in machines and machine tools (fig. 11-24). Weclassify cams as1. radial or plate cams,2. cylindrical or barrel cams, and3. pivoted beams.A similar type of cam includes drum or barrel cams,edge cams, and face cams.The drum or barrel cam has a path cut around itsoutside edge in which the roller or follower fits. Itimparts a to-and-from motion to a slide or lever in aplane parallel to the axis of the cam. Sometimes we buildthese cams upon a plain drum with cam plates attached.Plate cams are used in 5"/38 and 3"/50 guns to openthe breechblock during counter-recoil.Edge or peripheral cams, also called disc cams,operate a mechanism in one direction only. They rely ongravity or a spring to hold the roller in contact with theedge of the cam. The shape of the cam suits the actionrequired.11-12
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