A radial cam can turn a rotating shaft into a programmed straight-line motion. This calculator lets you divide one revolution into rise, upper dwell, return and lower dwell, then inspect how the actual profile moves a guided follower.
Cam Mechanism Interactive Calculator
Choose lift and the rise, dwell and return angles. The angular sliders share a 360° budget. Move the shaft-angle control to inspect a position; the follower and live results use the same angle.
Equation Used
- In-line ideal knife-edge follower with maintained return contact.
- One revolution contains the complete motion program. Each angular slider reserves space for the other entered events.
- Motion rate is mm per degree, not mm per second. No shaft speed or force is entered.
- Linear ramps create abrupt velocity changes at their boundaries; this is an educational program, not a high-speed design recommendation.
- The spring, guide and bearing identify the construction. Their forces, dimensions, stress and dynamic behavior are not calculated.
The follower position and displacement rate follow the shaft angle. Rise, upper dwell and return share one revolution; the remaining angle is lower dwell. A program exceeding 360° appears as an invalid geometry preview and cannot define a repeating cam.
A shaped disk and a guided follower
The cam turns around its fixed shaft. Its changing radius pushes an ideal pointed follower along a horizontal guide. The spring indicates how contact is maintained on return; it is not a calculated spring design.
The profile is generated by placing each requested follower position around the cam in the opposite direction of shaft rotation. At the current angle, the tip therefore lies on the same curve that supplies the displacement result. A finite roller would require a different profile, not simply a circle added to this tip.
Explore a motion program
Cams can coordinate repeatable displacement with shaft position. This demonstrator is useful for seeing how lift and angular timing change a basic profile. It does not select a cam material, bearing, motor or return spring.
Linear rise and return
Rise angle R moves the follower from 0 to lift L at slope L/R mm per degree. Upper dwell D holds it at L. Return angle F brings it back at slope −L/F. The remaining 360−R−D−F degrees are lower dwell.
These straight-line displacement ramps have abrupt changes in slope at their boundaries. They are not a cycloidal law. Shaft speed is not an input, so the result is displacement per degree rather than velocity per second.
The drawing uses an illustrative fixed base radius of 50 mm. Radius at contact is that base radius plus the calculated lift. Point-follower inversion defines the radial outline.
A 12 mm lift program
With a 90° rise, 60° upper dwell and 90° return, the lower dwell is 120°. At 45°, lift is 6 mm and motion rate is 0.133 mm/degree. At 120°, the follower is at its 12 mm upper dwell. At 195°, it is halfway down the return and the rate is −0.133 mm/degree.
Increasing one event reduces the available angular budget for the others. The sliders stop at the remaining available angle, preventing a motion program that cannot fit into one revolution.
What the simple program leaves out
Linear displacement segments make timing easy to understand, but their sudden slope changes imply abrupt velocity changes at constant shaft speed. Practical motion-law selection also considers acceleration, contact forces and structural behavior.
The drawing shows an ideal point follower. Finite tip geometry, friction, stiffness, cam loading and spring contact need separate analysis.
Questions about the cam
Why does an angle slider stop before 180°?
The other events already use part of the revolution. Its maximum reserves their entered angles so the total stays within 360°.
Does motion rate mean mm per second?
No. It is mm per degree of shaft rotation. Converting to time requires an angular speed.
Why are 0° and 360° the same position?
They are the same point in a repeating one-turn program.
Is the pointed follower a roller?
No. The drawing uses an ideal knife edge, whose trace is the profile. A roller needs an envelope offset for its radius.
Construction reference
Carnegie Mellon University, Introduction to Mechanisms, chapter 6: Cams. See the translating knife-edge construction, inversion method and discussion of constant-velocity motion and its abrupt velocity changes.
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