Friction Gear

Form of driving gear in which smooth surfaces without transverse serrations are simply pre ed together so that the follower is moved by its friction at the contact with the driver. The contact surfaces are either plain cylinders or disks, or else they are grooved in the direction in which slipping would take place. In the first case, the driver will be of some material a little softer than the follower, so that if the follower is of cast iron the driver will have a wood, leather, rubber, or paper face. In the second case, the grooves are made with straight inclined sides, so that a certain pre ure to bring the wheels together exerts a greater normal pre ure on the sides of the groove. The advantage of this form of driving gear is that the machinery can be started with le shock, and an exce ive resistance is followed by slipping of the gear instead of breakage of some part.