Torin T32052 - Cable Pulling Forces; Anchoring Force Considerations; Capstan Force Multiplication

9
CABLE PULLING FORCES
Cable Pulling Forces
This section provides detailed explanations and illustrations of the forces that are generated during the cable
pull. These explanations are based on the concepts presented in the last section, “Pulling Theory.”
At the Cable Puller Anchoring System
The cable puller will exert its maximum pulling force on cable puller’s anchoring system. It is extremely
important the anchoring system can withstand this amount of force. Refer to the instruction manual provided
with your anchoring system for proper setup or installation.
At the Capstan
The capstan acts as a force multiplier. The operator
exerts a small amount of tension, or tailing force, on the rope; the capstan multiplies this force to pull the
cable.
The resultant force depends upon the number of times the rope is wrapped around the capstan, as shown in
the formula below.
Pulling Force = Tailing Force x e0.0175μø
Where:
e = the natural logarithm, or 2.7183
μ = the coefcient of friction between the rope and the capstan*
ø = the number of degrees of wrap of rope around the capstan
* The average value for the coefcient of friction when double-braided composite rope is pulled over a clean
dry capstan is 0.125.
The following table is based on the formula above.
The input, or tailing force, is constant at 44.5 N (10 lb). Increasing the number of wraps increases the pulling
force.
This table shows how the capstan acts as a force multiplier. Because the coefcient of friction depends upon
the condition of the rope and capstan, this formula cannot determine an exact amount of pulling force.
Operator’s
Tailing Force
Number of
Wraps of Rope
Approximate
Pulling Force
44.5 N
(10 lb)
1 93.4 N (21 lb)
2 213.5 N (48 lb)
3 474.9 N (106 lb)
4 1043.8 N (233 lb)
5 2293.7 N (512 lb)
6 5048.9 N (1127 lb)
7 11.1 KN (2478 lb)