# Geometric Analysis: Cam Size

## Cam Size

Terminology that relates to 'Cam-Size'.

 • Base Circle: the diameter of the smallest circle that is tangent to the cam surface.
 • Prime Circle: the diameter of the smallest circle that is tangent to the Pitch-Curve.
 • Cam Lift (also called Follower Stroke): the difference between the 'Prime-Circle' and the maximum radius of the Pitch-Curve.

A smaller cam:

 • requires less space.
 • reduces material costs (but a 'very' small and 'very' large cam increase manufacturing costs).
 • reduces its inertia for rapid starting and emergency stopping.
 • reduces out-of-balance forces.
 • reduces the number-of-rotations that cam-follower roller makes for each rotation of the cam
 • reduces the angular velocity and angular acceleration of the cam-follower roller
 • reduces the sliding distance the flat-faced follower makes for each rotation of the cam, thus reducing wear
 • reduces the sliding velocity with flat-faced follower, thus reducing wear

A smaller cam:

 • reduces the flywheel effect. This helps to rotate the cam-shaft at constant angular velocity.
 • increases the accuracy required of a CNC machine tool to manufacture
 • increases pressure angle and reduces the radius of curvature [increases Hertzian Contact-Stress]

### Cam Size and the Measurement-Dimension FB

Measurement of the Base Circle, Prime Circle, Cam Lift

To measure the Cam, use a Measurement FB.

Basic Circle  [See image: Base-Circle = 80mm]

You may need to 'Filter Points' so that you only can click Points.

 2 Click the small Point at the contact between the Cam-Follower and the Cam
 3 Click the Point at the centre of the rotating Cam
 4 Click the graphic-area.

The Measurement-Dimension in the graphic-area continually updates as you cycle the model.

Look at the Measurement-Dimension in the graphic-area to find the minimum measurement - the Base-Circle Radius - in the image it is 80mm - or use a Graph FB to plot the radius.

Cam Lift

The difference between the minimum and maximum values of the Measurement-Dimension is the Cam-Lift.

You can also use a Stats FB to find the maximum and minimum values.

Prime-Circle (also called the Reference Circle) [See image: Prime-Circle = 100mm]

The Prime-Circle Radius is the minimum diameter from the centre of the cam to the centre of the Cam-Follower.