A release cam controls when a follower is held, lifted and allowed to return. This example divides one revolution into a low dwell, a rise and a high dwell, ending at an abrupt release edge. Enter shaft RPM and the dwell and rise angles to compare how long each stage lasts.
Release Cam Interactive Calculator
Set a positive shaft speed, low-dwell angle and rise angle. The remaining part of the revolution becomes high dwell. The calculator gives interval times; the drawing illustrates their sequence without calculating follower forces or return motion.
Equation Used
- Shaft speed is constant throughout one revolution.
- Low dwell plus rise is less than 360 degrees; the remainder is high dwell.
- The drawing represents a translating follower with a return spring; it does not solve roller contact geometry or spring loading.
- At the release edge, the illustrated follower jumps back to its low position. A real follower cannot return instantaneously.
How the release-cam cycle works
During the low dwell, the follower stays at its low position while the shaft turns. The rise moves it outward, and the high dwell holds it at the raised position. The release edge ends that hold.
The illustration uses a cubic rise with zero slope at its ends, followed by an abrupt reset at the release edge. This makes the timing stages visible. It does not describe the acceleration, impact or loss of contact during an actual spring-driven return.
Comparing cam timing
Use the calculator to allocate a revolution between holding and lifting intervals. Increasing RPM shortens every interval in the same proportion. At a fixed RPM, increasing either the low dwell or rise leaves less angle and time for high dwell.
The results describe timing only. They do not determine follower load, spring size, release velocity or whether a cam can perform a particular machine operation.
Constant-speed angular timing
The revolution period is 60/n seconds. For any interval angle beta, interval time is (beta/360)(60/n). The high-dwell angle is 360 degrees minus the entered low-dwell and rise angles.
The three interval angles add to 360 degrees. The release edge has no allocated angle or time here. At zero RPM the cam is stopped: the displayed zeros indicate that no cycle timing is being calculated.
Worked example
At 15 rpm, one cycle takes 4 seconds. A 320-degree low dwell lasts about 3556 ms, a 20-degree rise lasts about 222 ms and the remaining 20-degree high dwell lasts about 222 ms before the ideal release edge.
From timing to a working cam
A timing schedule is only part of cam design. The roller radius, follower travel, pressure angle, profile curvature and return motion must work together. An abrupt jump in the illustration does not establish a feasible cam surface or follower path.
A physical mechanism also needs checks of spring force, moving mass, impact, contact stress, material, lubrication and operating speed. The calculator does not supply those loads or component ratings.
Playback follows the entered period up to 30 RPM. At higher speeds the displayed revolution takes two seconds for visibility, while the numerical times continue to use the entered RPM.
Release-cam timing questions
Why is high-dwell angle not a separate input?
One revolution contains 360 degrees. After allocating the low dwell and rise, the remaining angle becomes high dwell. The ideal release edge has no allocated duration in this calculation.
Does the release edge predict return speed?
No. The animation resets the follower immediately at the edge. A real return takes time and depends on spring force, moving mass, load, damping and whether the follower loses contact.
Why do the timing cards show zero at zero RPM?
At zero RPM the cam is stopped and no cycle is completed. The calculator uses zero as its stopped display; this does not mean a physical revolution or dwell takes zero time. Enter a positive RPM to calculate interval durations.
Does playback always match the entered RPM?
Playback matches the revolution period up to 30 RPM. Above that speed it is slowed to two seconds per displayed revolution so the motion is easier to see. The timing cards still use the entered RPM.
Can I machine this drawing as a cam profile?
No. It illustrates angular timing and an abrupt release. Roller contact geometry, pressure angle, curvature, forces and a physically achievable return motion need separate design.
Is the linked quick-release lever the mechanism in the calculator?
No. The video shows a hand-operated cam lever for fastening. The calculator illustrates a continuously rotating cam with dwell, rise and release intervals. They are different cam applications.
Technical references
- Carnegie Mellon University, Chapter 6: Cams — rise, dwell and return motion intervals.
- University of Florida, Properties of Cams — spring-return follower and cyclic cam geometry.
- Ohio University, Disk Cam Design Example — angular motion allocation and smooth motion laws.
- CN116897112B — distinct dwell and release portions and angles.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
