The factor that decides the size of the cam is

Concept:

• Base Circle: It is the smallest circle, drawn tangential to the cam profile. The base circle decides the overall size of the cam and thus is a fundamental feature.
• Pitch Curve: If we hold the cam fixed and rotate the follower in a direction opposite to that of the cam, then the curve generated by the locus of the trace point is called a pitch curve. For a knife-edge follower, the pitch curve and the cam profile are the same whereas, for a roller follower, they are separated by the radius of the roller.
• Pitch Point: Pitch point corresponds to the point of maximum pressure angle, and a circle drawn with its center at the cam center, to pass through the pitch point, is known as the pitch circle.
• Prime Circle: It is the smallest circle that can be drawn from the center of the cam and tangent to the pitch curve.