or rotate appreciably after it has been released from the driving member. The heavier the clutch cone, the greater will be its inertia or tendency to revolve, due to the power stored in its rim.

Q. What materials are used to face the clutch cone with? A. The clutch cone is usually faced with a good grade of oak tanned sole leather though in some cases asbestos fabrics have been used with success. In some constructions the cone is of metal, studded with cork inserts, though as a rule the cone is faced with leather even if cork inserts are used. Materials are used for facings that are not likely to be affected by oil or heat and that have a high coefficient of friction with cast iron of which the female member is invariably composed.

Q. What does "coefficient of friction" mean?

A. The "coefficient of friction" is a term used to indicate the amount of frictional adhesion various materials have for each other under similar conditions of pressure.

Q. Name the "coefficient of friction" of various surfaces in

contact.

A. A table of triction coefficient of various materials compiled from tests made by the Cork Insert Co. follows:

The coefficient will vary with condition of the contacting surface. Smooth and hard surfaces offer less resistance than rough and yielding ones. In metal to metal clutches different materials are usually employed for the opposing surfaces such as bronze and steel

in multiple disc clutches or cast iron or bronze and steel in three plate types. A coefficient of friction of 0.10 means that the adhesion between the surfaces will be 10% of the total pressure producing frictional contact. Therefore, a combination leather and cork friction facing acting against dry cast iron, as in a cone clutch, and having a coefficient of 0.35 will adhere to the member against which it contacts with a force equal to about % of that keeping the surfaces in contact.

Q. How is clutch cone kept in contact with female member? A. The clutch cone in practically all cases is held in engagement with the female member by the pressure of one or more coil springs. In some constructions the clutch cone is brought into engagement by means of levers actuated by some member that can be locked in place to hold the parts in contact until released.

Q. What is the function of the ball thrust bearing?

A. As will be observed by referring to Figs. 143 to 145 in no case is the spring pressure applied directly to the clutch cone and a ball thrust bearing is always interposed to take the spring thrust against the cone. This is used in order to permit the parts to operate independently of each other when the clutch cone is moved so the spring is compressed. The ball thrust bearing has so little friction that the full spring pressure may be exerted against it without causing rotation of the cone when that member is out of engagement with the flywheel rim. If no ball thrust bearing was used when the clutch cone was pushed away from the female member, the spring in contact with the driving member would tend to impart its rotary motion to the clutch cone and keep it turning when it is desirable to have it stop when released.

Q. What are the advantages of the cone clutch?

A. The cone clutch is a very simple form that is easy to operate and understand. When properly designed it will transmit the entire power of the motor to which it is applied without slipping and it can be made to release promptly and to engage gradually if desired.

Q. What is the main disadvantage of a cone clutch?

A. Owing to the mass of the clutch cone and its leather facing

there is a tendency for the cone to continue to rotate when released from driving engagement with the flywheel. The rim of even the lightest cone and its leather facing have appreciable weight, and while this is not much it is carried at a sufficiently large radius from the center so the cone has considerable momentum and acts, to some extent, as a flywheel. This continued rotation is called "spinning" and is objectionable, because it makes gear shifting difficult.

Pope-Hartford Cars.

Q. How is "spinning" prevented?

A. Continued rotation of the clutch cone is easily prevented by applying some form of braking member which will come in contact with the revolving cone after it has been pulled clear of the flywheel. A simple clutch brake is shown at Fig. 146. The friction pad A is carried by the clutch shifter yoke B in such a way that it comes in contact with the clutch cone only when this has been withdrawn a certain distance by the yoke F and the rolls G, as previously described. Suitable adjustments are provided at C, D, and E, so

the friction pad may be brought into engagement with the cone at any time that is desirable and in order to compensate for wear or other depreciation of the friction pad A.

Q. Describe three plate clutch and explain its action.

A. Two forms of three plate clutches are in general use; that outlined at Fig. 147 uses a large number of small springs to produce the pressure required to keep the parts in contact, while the form

Fig. 147.-Principal Parts of Knox Three-Plate Clutch.

depicted at Fig. 148 utilizes one main spring. A three plate clutch is so called because the central driven member serving to drive the clutch shaft connected to the gearset is sandwiched in between driving plates carried by the flywheel. In the Knox clutch shown at Fig. 147 the clamping pressure to keep the driving plates in firm. contact with the driven plate is obtained from a series of clutch springs carried near the flywheel rim. As the total pressure exerted by these springs is somewhere in the neighborhood of a thousand

Fig. 148.-Showing Construction of Three-Plate Clutch in Which Spring Pressure is Augmented by Levers to Increase Adhesion Between Clutch Members.

pounds it is necessary to provide some form of leverage so the inner and outer driving plates may be separated without undue exertion on the part of the operator. As will be evident in the clutch shown at Fig. 147 any pressure exerted against the long arms of the levers