Understanding Cam Throw and Follower Movement

In cam-follower mechanisms, the cam's profile dictates the movement of the follower. The "throw" of a cam is a fundamental parameter that describes the total displacement or lift imparted to the follower during one revolution of the cam.

What is the Base Circle?

The base circle of a cam is the smallest circle that can be drawn tangent to the cam profile. When the follower is at its lowest position, it is in contact with the cam profile at a point on or near the base circle. This position is often considered the zero-lift point for the follower.

Defining Cam Throw

The throw of a cam is defined as the maximum distance the follower moves radially outwards from its lowest position. Since the lowest position corresponds to the follower being on the base circle, the throw is the maximum lift or displacement measured from the base circle.

• Throw = Maximum follower distance from base circle - Minimum follower distance from base circle
• In most standard designs, the minimum follower distance from the base circle is zero (when the follower tip is tangent to the base circle).
• Therefore, the throw simplifies to the maximum distance of the follower from the base circle.

Other circles mentioned, like the pitch circle or prime circle, are also important in cam design, but the throw specifically relates to the total movement from the absolute lowest point, which is defined by the base circle.

Thus, the throw of a cam is the maximum distance of the follower from the Base circle.