A cam-lever grip brings an eccentric cam against a rod or rope. Rotating the cam changes the distance from its fixed pivot to the contact surface. This illustration uses a circular eccentric, a vertical rod and a compliant backing to make clearance and contact visible.
Cam-lever Grip Interactive Calculator
Set eccentricity, closing angle, combined clamp stiffness and free gap. The cam takes up the gap before generating force. Watch live contact through the sweep, while the result cards show the selected endpoint.
Equation Used
- Rigid circular cam with offset e from its fixed pivot and a flat rod contact surface.
- Linear combined stiffness k after clearance g is exhausted; deflection is enlarged in the illustration.
- Endpoint result cards and live animation values are distinguished. The cycle sweeps to the entered angle and returns.
- Past-peak rotation can reduce force. Locking requires a suitable stop and complete force-path analysis, not just a positive angle.
- No frictional holding force, rope damage, component strength, lifting capacity or safety-device rating is calculated.
Original four inputs and equations retained. The animation now makes eccentric closure, clearance take-up and compliant contact agree. Over-centre is an angular description, not a guaranteed lock or holding rating.
From free gap to clamping contact
Hiscox figure 1065 shows a cam lever gripping a vertical rope or rod against a backing surface. In this simplified circular-eccentric version, the shaft stays fixed while the cam centre travels around it. The left edge of the cam moves toward the rod.
Initially that movement takes up the entered gap. After contact, further closure deflects the combined clamp compliance and creates force. The enlarged backing spring is a visual representation of that compliance, not a specified component. The cam and rod remain in contact without overlapping.
Understanding the gripping principle
The mechanism converts a short lever rotation into closure at a gripping surface. The calculator isolates eccentric geometry and a linear elastic response. It does not rate a grip for a suspended load or reproduce an elevator safety device.
Closure and elastic force
For eccentricity e and rotation θ measured from minimum closure, h=e(1−cosθ). The gap g produces no force until h exceeds g. Thereafter the combined stiffness k gives F=k(h−g).
Maximum geometric closure is 2e at 180°. Past that point, closure and force decrease. A positive angle past 180° does not establish that a lever will stay there: a stop, load path and friction conditions matter.
Try clearance and stiffness
With e=3 mm, θ=190°, k=1,000 N/mm and zero free gap, closure is approximately 5.95 mm and the linear model gives approximately 5,954 N. A 2 mm gap reduces compression and force to approximately 3.95 mm and 3,954 N.
If the gap exceeds 2e, the cam cannot close it at any angle. The diagram then keeps showing the open clearance and zero force. These calculated forces are not component ratings.
Geometry is not a lock rating
This model makes the consequences of eccentricity, angle, gap and stiffness visible. It does not include frictional holding capacity, material limits or a lever stop. The displayed force is only the chosen linear-compliance result.
Questions about the grip
Why is force zero while the lever moves?
The cam may still be taking up the free gap.
Why does force fall past 180°?
The circular eccentric has passed maximum closure.
Does a positive angle past peak mean the grip is locked?
No. The model does not include the stop and full force path needed to establish that condition.
Is the illustrated spring a required part?
No. It makes combined elastic compliance visible.
Construction reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, page 265, figure 1065: cam-lever grip against a vertical rod or rope. The enlarged compliance illustration and numerical circular-eccentric model are explanatory additions.
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