What is "Exerting/Clamping Force" & "Holding Capacity"?
In the case of clamping products, a clear distinction must be made between exerting forces and holding capacities. Here are the essential features.
Exerting or Clamping Force
Manually operated clamps present a series of variables to determine actual exerting force. These variables are:
- the force exerted on the handle by the operator;
- the point on the handle where this force is applied;
- the mechanical advantage in the linkage; and
- the point on the work holding bar where the force will be measured. As a general rule, the mechanical advantage available throughout the line ranges from 2:1 to 10:1
The “holding capacity” of Destaco toggle clamps has been determined by actual tests. It is defined as the maximum amount of force which may be applied to the work holding bar, in the closed position, without creating permanent deformation of the clamp components. This maximum force is measured at a point closest to the base and diminishes as the spindle approaches the end of the bar. The ratings for holding capacity are maximum and should not be exceeded. These values include a safety factor.
Diagram: Exerting Force, Clamping Force & Holding Capacity
How to Calculate Exerting or Clamping Force?
The table below depicts holding capacity (HC) and clamping force (EF) data for a typical manual clamp. The clamping force (EF) is expressed as a ratio of the force that is applied to the clamp handle (AF). In this example, either 10:1 or 5.3:1 depending upon position of the clamping point on the clamp arm. That is, at position X1, the maximum clamping force (EF) that can be generated is 10 times the force that is applied to the clamp handle.
- Example #1 - Find the force (AF) the operator would have to apply to the clamp to generate a clamping force of 90N [400lbf.] at the end of the clamp arm (X1).
AF = 90 ÷ 10 = 9N [40lbf.]
- Example #2 - What is the maximum clamp force that can be generated at X2 if the operator is only able to apply 5N [23lbf.] to the clamp handle?
EF = 5 · 5,3 = 26,5N [120lbf.]
How to Calculate Holding Capacity?
The holding capacity (HC) ratings shown in the table are in relation to the pivot point of the clamping arm. This is useful in estimating the holding capacity at an intermediate clamping point along the arm, or at a point beyond the length of the standard clamping arm.
- Example #1 - Find the maximum holding capacity if the clamping point is 40mm [1.5in.] from the front of the base of the clamp.
- Step 1 – find the clamping distance from the clamping point to the pivot point
Xc = 40mm + X = 40mm + 40,5mm = 80.5mm
- Step 2 – express the holding capacity as a moment
M = X1 HC1 = 49,5mm x 4450N = 220275 N mm
- Step 3 – calculate the holding capacity at XC
HC = M ÷ Xc = 220275 ÷ 80,5 = 2736N [615lbf.]
- Example #2 - Find the maximum holding capacity if the clamp arm is extended by 25mm [1in.] (follow steps 1-3 above)
Xc = 25+X2 = 25 + 99,5 = 124,5mm
M = X2 HC2 = 99,5mm 2090mm = 207955 N mm
HC = M ÷ Xc = 207955 ÷ 124,5 = 1670N [375lbf.]