[TowerTalk] Gluing rope

[donovanf at starpower.net]

Tod,

A sheave is the grooved wheel in a pulley or block.  

In antenna support applications, there is often a great deal of rope motion over a pulley during windy conditions.  Rope wearout is usually caused by this repeated motion.  

An incorrectly sized sheave will significantly reduce rope life if:
 - the diameter measured at the center of the groove is less than eight times the rope diameter, or 
 - the depth and width of the U-shaped groove is improperly sized so that it does not support at least 1/3 of the rope circumference.

A sheave should be sized so that the sheave diameter measured at the center of the U-shaped groove is at least eight times the rope diameter.  Rope life will be extended with increased sheave diameter.

The width of the U-shaped groove should be approximately 10 percent greater than rope diameter.  The depth of the U-shaped groove should be approximately 1/2 the rope diameter.  If you change rope diameter, the pulley should always be replaced with a new pulley with the correct groove width and depth.  

You can extend rope life by rigging the rope so that it wraps around as little of the sheave circumference as possible.  A rope that wraps around half of the sheave circumference will have a much longer life than a rope that wraps almost entirely around the sheave.

73
Frank
W3LPL

---- Original message ----
>Date: Sat, 19 Sep 2009 08:31:47 -0600
>From: "Tod - ID" <tod at k0to.us>  
>Subject: RE: [TowerTalk] Gluing rope  
>To: <donovanf at starpower.net>
>
>Frank:
>
>>To avoid premature rope 
>> failure, the sheave diameter should be at least eight times 
>> the diameter of the rope.
>
>I want to be sure that I understand correctly. Is the sheave diameter the
>diameter of the pulley or the diamter of the groove in the circumfrence of
>the pulley.
>
>For the example of using 1/8" rope that would suggest the diameter of the
>pulley used be 1" or more. Or you might mean that the the groove in the
>circumfrence of the pulley would have a groove diameter of 1" or more.
>
>I am inclined to guess that the diameter of the pulley should be > 1" and
>the groove diameter should be slightly greater than 1/8".to assure that the
>rope wear is not excessive.
>
>
>
>Tod, K0TO
>