Winch drum and cable wrap question
Winch drum and cable wrap question
(OP)
I'm in the process of writing a report on a winch drum failure. Our winches are wrapped around the drum and then terminated with a u-bolt on the flange of the drum. The customer is stating that the cable slipped out from under the u-bolt. This may have happened but I want to know how I could estimate the force required to do this. The question really comes down to the number of wraps (not layers) on the drum itself. The more wraps the less force is actually exerted on the u-bolt. I'm estimating that there were 3 total wraps on a 5" diameter winch using 3/8" cable. I know this is a loaded question where many outside factors could come into play, however, I'm just trying to understand the basic math behind the idea. Any thoughts?
-Thanks
-Thanks





RE: Winch drum and cable wrap question
T2/T1 = e ^ (mu*B)
where mu = coefficient of friction
B = arc of contact in radians
RE: Winch drum and cable wrap question
I'm confused on what this equation is really giving me. I've attached a picture for more clarification of what I'm talking about. What I am gathering (which could be wrong) is that if I make a single wrap around a winch drum (cylinder) and input a force T2, then T1 is the force on the opposing side of the winch drum. I looked up a steel on steel coefficient of friction and found it to be 0.8. The arc radius if I assume 1 wrap is 2pi. I used the equation posted above to calculate the "output tension" of the cable and got 0.05 lbs? The strange part is that based on this equation the output tension would increase with wraps not decrease. I know I could be twisting this up and thinking about it all wrong so hopefully you can provide some insight.
Thanks
RE: Winch drum and cable wrap question
Your value of .8 for the coefficient of friction is not very conservative. If you want to know the worst case load on the clamp (attached to the end called T1 in your sketch and connected to the rotating drum) then you should assume a low value for the c.o.f. (.1 is fairly common)
RE: Winch drum and cable wrap question
RE: Winch drum and cable wrap question
RE: Winch drum and cable wrap question
Just out of curiosity do you know where you got that equation? Since I am writing a report I would like to back it up with some type of source just in case anyone questions the validity of my findings. Thanks again for the help.
RE: Winch drum and cable wrap question
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RE: Winch drum and cable wrap question