Cam Nomenclature:

Given fig shows a disc cam with a roller follower. Having reference to this figure we will define several terms that are used very frequently.

Base Circle:

This is the circle drawn having centre at the centre of rotation of the cam & radius equivalent to the smallest radius. This is tangent to the cam contour.

Trace Point:

This is a theoretical point on the follower. This is motion explain the movement of the follower. For the knife edge follower, trace point is at the knife edge and for a roller follower; trace point is at the roller centre.

Pitch Curve:

This is the curve drawn by trace point supposing that the cam is fixed, & the follower is taken around the cam in a direction just opposed to the cam rotation. For knife edge follower, the pitch curve & cam contour are the same.

Pressure Angle (φ):

This is the angle among the normal to the pitch curve & the direction of the follower motion at a point. It differs like the point of contact changes. At the guides higher value of pressure angle results in higher value of side thrust.

Pitch Point:

This is the point on the pitch curve at which the pressure angle is utmost.

Pitch Circle:

This is the circle passing through the pitch point & this is concentric having base circle.

Prime Circle:

This is the circle of smallest radius that can be drawn along centre at the centre of cam rotation so that this is tangential to pitch curve. On behalf of a roller follower, the radius of prime circle shall be equivalent to minimum cam radius as well as radius of the follower. For knife edge follower prime circle & base circle are similar.