To change the direction of a motion, we use cams with the linkage. Rocker arms are merely a variation, or special use, of levers. Bell cranks primarily transmit motion from a link traveling in one direction to another link moving in a different direction. The bell crank mounts on a fixed Figure 11-14. 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. The term coupling applies to any device that holds two parts together. Line shafts that make up several shafts of different lengths may be held together by any of several types of shaft couplings. It consists of a metal tube slit at each end.