A linkage may consist of either one or a combination of the following basic parts:

    1. Rod, shaft, or plunger

    3. Rocker arm

    4. Bell crank

These parts combined will transmit limited rotary or linear motion. To change the direction of a motion, we use cams with the linkage.

Lever-type linkages (fig. 11-14) are used in equipment that you open and close; for instance, valves in electric-hydraulic systems, gates clutches, and clutch-solenoid interlocks. Rocker arms are merely a variation, or special use, of levers.

Figure 11-14.Linkages.

pivot, and the two links connect at two points in different directions from the pivot. By properly locating the connection points, the output links can move in any desired direction.

All linkages require occasional adjustments or repair, particularly when they become worn. To make the proper adjustments, a person must be familiar with the basic parts that constitute a linkage. Adjustments are normally made by lengthening or shortening the rods and shafts by a clevis or turnbuckle.

You may use the sleeve coupling (fig. 11-15) when shafts are closely aligned. It consists of a metal tube slit at each end. The slitted ends enable the clamps to fasten the sleeve securely to the shaft ends. With the clamps tightened, the shafts are held firmly together and turn as one shaft. The sleeve coupling also serves as a convenient device for making adjustments between units. The weight at the opposite end of the clamp from the screw merely offsets the weight of the screw and clamp arms. Distributing the weight evenly reduces the shaft vibration.

The Oldham coupling, named for its inventor, transmits rotary motion between shafts that are parallel but not always in perfect alignment.

An Oldham coupling (fig. 11-16) consists of a pair of disks, one flat and the other hollow. These disks are pinned to the ends of the shafts. A third (center) disk, with a pair of lugs projecting from each face of the disk, fits into the slots between the two end disks and enables one shaft to drive the other shaft. A coil spring, housed within the center of the hollow end disk, forces the center disk against the flat disk. When the coupling is assembled on the shaft ends, a flat lock spring is slipped into the space around the coil spring. The ends of the flat spring are formed so that when they are pushed into the proper place, the ends of the spring push out and lock around the lugs. A lock wire is passed between the holes drilled through the projecting lugs to guard the assembly. The coil spring compensates for any change in shaft length. (Changes in temperature may cause the shaft length to vary.) The disks, or rings, connecting the shafts allow a small amount of radial play. This play allows a small amount of misalignment of the shafts as they rotate. You can easily connect and disconnect the Oldham type couplings to realign the shafts.