How a Friction Clutch is Made.—A friction clutch consists of two chief parts and these are (1) the shell half and (2) the mechanical half. The shell and its hub is of iron and forms a perfectly smooth friction surface.
The mechanical half is made up of a driving plate on which an expansion ring is mounted, and this consists of two or more segments according to the size of the clutch. These segments can be forced apart or expanded, so that the wood friction shoes, which are bolted to them, are brought into contact with the inside of the shell by means of a right and left thread screw lever which run in nuts and which set in the opposed ends of the expansion ring and are held in position by a screw and shoe.
The right and left screw lever is worked by a powerful toggle which in turn is operated by a slid ing sleeve. The combination of the right and left threaded screw makes a positive acting device of great power. At the outside end of the mechanical half is a yoke for securing the hand shifting lever to the sliding sleeve.
Finally, there is a balance weight to counterbal ance the lever and toggle and this prevents the cen trifugal force from throwing the clutch in gear when it is running at a high speed. A longitudinal cross
section of the clutch is shown at A in Fig. 74, a transverse cross-section of it is shown at B, and the clutch complete at C.
For small engines the clutch, which is also used for a pulley, is worked by a hand wheel as shown at A in Fig. 75, but for larger engines it is operated by a lever, as shown at B.
Split Friction Clutches.—A split friction clutch is made in halves so that it can be put on the ad jacent ends of the lengths of a line of shafting al ready in place, and can be readily installed with out taking down the shaft or disturbing any of the equipment upon it. Then again, it affords the greatest ease in taking off old parts and putting in new parts should any repairs or renewals be neces sary.' Magnetic Clutches.—This type of clutch is con structed on the same general principle as the one described for mobile engines. It is chiefly used for stationary power installations where electric gen erators or converters are to be started up and which must not too greatly disturb the load.'