[TowerTalk] Turnbuckle-Gate & Ginpole sheaves

[Kurt Andress]

Interesting threads about fetched up or out-of-control turnbuckles and
getting rope to happily go around a ginpole sheave..

The last comments by Patrick Dayshaw and WB0W made me stop long enough to
comment. 

Preface: I have spent the last 10 years designing, building, and servicing
composite spars for sailboats. Whenever, a simple mistake results in the
failure of any component of the spar system, someone has to get on an
airplane and go to some remote part of the world and fix it! Simple
mistakes tend to be cost prohibitive!

Turnbuckles - There are really two threads here.
1) What causes threaded connections to fetch up? 2) How do we stop threaded
connections from getting loose?

1A) Identical materials will always gaul or lock up in a highly loaded
threaded connection, if they are not isolated from each other by a solid
lubricating compound. 
The various compounds vary, but they share the same feature. A solid
particulate material, that is different from the base materials in the
threaded connection, and a paste or liquid vehicle that carries the solid
particles. Initially, these "anti-seize" products work because the liquid
in the compound readily distributes the solid particles to all surfaces of
the threaded interface. After time and the environment drives the paste or
liquid from the connection, the solid particles are left. Because they are
either softer, or harder, than the mating materials, they act as isolating
layer between the parent materials to prevent seizing or gauling of the
threads. 
The seizing of similar materials occurs when one surface is disturbed by an
imperfection in the other surface. This can be started by the simplest of
contaminants. A grain of dust, salt, sand, or a burr on one surface digs
into the mating surface and starts to raise a ball of material. The ball
continues to roll up until it jambs between the two surfaces and starts to
create a second ball on the other surface. Then the two act together to
pack material into the connection until it locks up.
The disimilar material in the anti-seize compound acts as a sacrificial
buffer by allowing itself to breakdown and prevent the formation of burr in
either of the mating surfaces.
This is exactly why so many have sworn not to use stainless nuts & bolts on
their antennas. They have proven, beyond a shadow of a doubt, that if one
puts them together without a lubricant, they will gaul and seize! This is
not an endorsement for non-stainless fasteners, it is an endorsement for
intelligent use of stainless, which requires the understanding of sound
practices.

Just in case somebody hasn't got it yet, you can't put identical alloys
together in a threaded connection without putting an anti-seizing compound
in the way of the threads! Well, I must admit, my statment is not absolute.
You can put identical alloys together in a threaded joint, you need to know
that you may get away with it only once or twice, before it locks up!
Just for the pundits, the reason why you get away with multiple cycles of
assembling zinc plated steel fasteners is the zinc plating! It acts as the
solid lubricant for the thread interfaces. Keep turning these fasteners,
until the zinc goes away, and you'll get fetched up in the end!


The other reason for having threads lockup is corrosion. This is way after
the initial installation, and is usually caused by the knucklehead before
you putting everything together without anti-seize paste!

1B) Stopping turnbuckles from unwinding is childs play. This has been done
by every sailboat rigger in the last 50 years. Since, every time a
turnbuckle undoes itself, a mast falls down, damaging an expensive boat, or
sinks the boat, or kills members of the crew, it is not left to chance. All
marine turnbuckles provide positive locking features. The threaded shafts
of the turnbuckle are drilled to accept split pins ( that's cotter pins to
the US gang). These split pins are inserted into the shafts of the
turnbuckle ends, inside the body of the turnbuckle cage, or housing. This
prevents the end shafts from turning when the cotter pins bind up on the
body of the center section of the assembly. If you want to do it this way,
just drill small holes in the ends of your turnbuckle shafts and put split
pins in them!
Another easy method is to provide a jam nut on the right hand threaded end
of the turnbuckle. We cannot buy turnbuckles with a jam nut, they are not
sold that way. We just need to take the thing apart and put our own jam nut
on it, then lock it when we are done adjusting the guys. Then, of course,
we add the safety loops through the turnbuckle and anchor.

Lines traveling over sheaves are a different subject.
Whether on a ginpole or any other device, the solution is the same. The
sheave needs to be designed for the size of line to be used.
In my field, every time it is improperly done, somebody gets on an airplane
and goes far away to fix it! Certainly more expensive than somebody
complaining about it on towertalk!
Any line will flatten out when highly loaded around a sheave. If the volume
of the groove in the sheave is too low, the line will splay out and get
packed into the gaps betwen the sheave and the side supports. This damages
the line jacket resulting in visible deterioratioin of the line. I would
suggest that the ginpole manufacturers design their sheaves for a
particular line size and make the line size a part of their specifications.

What line size is the most popular is not clear. I haven't seen a post from
a professional ground crew member yet. I have my own opinions, but then
they would only be anecdotal nonsense. We do know that bigger is better!
It sounds like the line size that is comfortable for the ground crew would
have a safety factor of 4 for the lifting load.

73, Kurt


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