Fig.3.7

**Pressure angle: **It is the angle between the direction of the follower motion and a normal tothe pitch curve. This angle is very important in designing a cam profile. If the angle is too large, a reciprocating follower will jam in its bearings.

**Base circle: **It is the smallest circle that can be drawn to the cam profile.

**Trace point: **It is the reference point on the follower and is used to generate the pitch curve.In the case of knife edge follower, the knife edge represents the trace point and the pitch curve corresponds to the cam profile. In the roller follower, the centre of the roller represents the trace point.

**Pitch point: **It is a point on the pitch curve having the maximum pressure angle.** Pitch circle: **It is a circle drawn from the centre of the cam through the pitch points.

**Pitch curve: **It is the curve generated by the trace point as the follower moves relative to thecam.For a knife edge follower, the pitch curve and the cam profile are same where as for a roller follower; they are separated by the radius of the follower.

**Prime circle: **It is the smallest circle that can be drawn from the centre of the cam andtangent to the point.For a knife edge and a flat face follower, the prime circle and the base circle and the base circle are identical.For a roller follower, the prime circle is larger than the base circle by the radius of the roller.

**Lift (or) stroke: **It is the maximum travel of the follower from its lowest position to thetopmost position.

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