Controlling the Holding Force of a Clamping Fork via Screw Position

Controlling the Holding Force of a Clamping Fork via Screw Position

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Clamping Forks: Tip for Maximizing the Holding Force


Clamping force applied by the CL2 clamping fork
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Figure 2: More than half the total applied force (FTotal ) holds the object, since LL2. The height of the left leg of this CL2 clamp is variable to compensate for the object's height. This allows the clamp's top surface and the mounting surface to be made parallel.**

Clamping force applied by the CLA5 clamping fork
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Figure 1: Less than half the total applied force (FTotal ) holds the object, since LL2. The clamp illustrated above is the CL5A.

Clamped objects can be fairly easy to move when the torqued screw in the clamp's slot is positioned too far from the object. Correct positioning of the screw protects clamped objects from being knocked out of position.

To maximize the clamping force, position the screw as close as possible to the object.**

This works since clamps like CL5A and CL2 (Figures 1 and 2, respectively) divide the torqued screw's applied force (FTotal ) between two points.

Clamping force F2 is applied to the object. The value of F2 is a percentage of FTotal and depends on L1 and L2, as described below. The remainder (F1) of the total force is applied through the opposite end of the clamp.

The following equations can be used to calculate the two applied forces. 

Force Applied to Object :  Force Applied to the Other Contact Point: 

These equations show that the clamping force on the object increases as the distance between the object and screw decreases. The force supplied by the torqued screw is evenly divided between F1 and F2 when L1 and L2 are equal.

**Note that maximizing the clamping force also requires both the top surface of the clamp and the area it contacts on the object to be parallel with the mounting surface, as depicted in Figures 1 and 2.

If the tangent at the interface between the clamp and object is not parallel to the mounting surface, the force applied to the object will be divided between pressing it into and pushing it across the mounting surface. The force directed along the mounting surface may, or may not, be sufficient to translate the object.

To accommodate different object heights, clamps like the CL2 have one threaded, variable-length leg, which is shown on the left in Figure 2. The number of threads between the clamp and mounting surface should be adjusted to compensate for the height of the object and to keep the clamp's top surface level with the table.   

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Date of Last Edit: Dec. 4, 2019

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