Geometric Analysis: Cam Size

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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.

Advantages of a 'smaller' Cam.

A small cam:

requires less space

reduces material costs (however, 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

Disadvantages of a 'smaller' Cam.

A small cam:

reduces the flywheel effect. A Flywheel helps to rotate the cam-shaft with a constant angular velocity

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.

Top-tip: To select Points only, use Filter menu > Filter Points.

Top-tip: Remember to turn Filter-Points OFF after you ave selected the Points !

Basic Circle

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

1.Click Add menu (or Kinematic FB toolbar) > Measurement FB

2.Click the small Point Red-14-1bat the contact between the Cam-Follower and the Cam

3.Click the Point at the center of the rotating CamRed-14-2

4.Click the graphic-area.

The Measurement (and the FB)Red-14-4 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 measurement values.

Prime-Circle (also called the Reference Circle)

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

1.Click Add Measurement FB

2.Click the Point at the center of the Cam and then the center of the Cam-Follower.Red-14-3