as we know, cam is a transmission mechinary just like as gear , worm and so on . it can change the motion into different direction and speed . many machinary designers adopt cam motion as their first choice of conception . especial in designing engine, cam motion is one of five crital components of engine . it supply a lift motion to tappet , and then tippit press or release the inner air's volumn of cylinder, and finally aim to fire oil to come out work of engine.