6000-Series Super Tugger
®
Cable Pullers
Greenlee Tools, Inc.
4455 Boeing Dr. • Rockford, IL 61109-2988 USA • 815-397-7070
12
Cable Pulling Principles
(cont’d)
Cable Pulling Forces
(cont’d)
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 e
0.0175µø
Where:
e = the natural logarithm, or 2.7183
µ = the coefficient 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 coefficient 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.
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)
This table shows how the capstan acts as a force
multiplier. Because the coefficient of friction depends
upon the condition of the rope and capstan, this formula
cannot determine an exact amount of pulling force.
The Capstan as a Force Multiplier
Pulling Force: 28.9 kN (6500 lb)
Tailing
Force
