Why should I leave at least two turns of wire rope on the crane reel?

In order to facilitate inspection and assembly and disassembly, wire rope in the reel connection fixed commonly used wedge-shaped block pressure plate and cover plate and other methods. But no matter which method connection fixed, wire rope in the reel must leave two circles as a safety circle. This is why? First of all, we have to start from the force relationship.   

In a cylinder winding a rope, if the a end force F 1 to pull, to make the rope not in the cylinder on the relative slide, then the b end will have to act a force F 2. Because the rope and the cylinder between the existence of friction, so F2 less than F1. and the difference between them with the rope in the cylinder winding the number of turns to increase and increase. If the coefficient of friction between the rope and the cylinder f = 0.16, when winding two turns, in the role of F1, the rope and the cylinder does not produce relative sliding condition is F2>= 0.134F1. The above situation and the steel wire winding on the reel situation is similar, a end of F1 is equivalent to the weight of the lifting object, b end is the fixed end of the wire rope and reel connection. In the design, the fixed end is according to the wire rope winding two circles of the situation to consider, that is, in accordance with the fixed end of the steel rope only by the maximum pull 0.134 times the design. So in order to be safe, the wire rope in the reel to stay at least two turns. At the same time, also because stay on the reel wire rope reduces the fixed end of the steel wire force, can prevent the wire rope is pulled off or pressure plate, bolt by the destruction, to ensure the connection fixed safe and reliable, so called safety circle or reduce the load circle.