# 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 small 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

A small cam:

 • reduces the flywheel effect. This helps to rotate the cam-shaft at constant angular velocity. However, this effect is usually quite small.
 • increases the accuracy required to manufacture.
 • increases pressure angle and reduces the radius of curvature , which increases Hertzian Contact-Stress.

### Cam Size and the Measurement-Dimension FB

To measure the Cam with a Measurement FB, we will click different Points.

If necessary, to select Points only, use Filter menu > Filter Points.

Basic Circle

The radius of the Base-Circle is the minimum radius from the centre of the cam to the contact between the cam and the cam-follower.

 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 (and the FB) are now in the graphic-area . The Measurement will increase and decrease when you rotate the cam.

When the Measurement is a minimum - you have found the radius of the Base-Circle

Cam Lift

The difference between the minimum and maximum values given by the Measurement FB 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)

The radius of the Prime-Circle is the minimum radius from the centre of the cam to the centre of the cam-follower.