[TowerTalk] Crank-UP Tower Cables.

[John Cramond]

In message <F2713MgPPf3L9BGTuAy00000ed2@hotmail.com>, Ted Leaf
<tleaf@hotmail.com> writes
>Hi guys,
>
>If the most common reason for crank-up tower failure is due to rusted 
>cables, why is it that the most popular manufacturer (U.S. Towers) doesn't 
>offer the option of stainless steel cables?
>
>I understand that SS cable has about 10% less breaking strength than 
>galvanized, but using a slightly larger cable would compensate.
>
>I would think that many hams would be glad to pay the additional cost.
>
>Please post your replies directly to TowerTalk and not to me--I will see 
>them there.
>
>Thanks.
>
>73, Aloha
>Ted Leaf, K6HI
>Kona, Hawaii
><tleaf@hotmail.com>
Hello Ted,

There are three main causes of wire failure on crank up towers. Lack of
maintenance, overload, and incorrect spooling.

Stainless cables are mainly manufactured for supporting static loads.
They will not provide reliable service when used for live loads due to
the continual flexing of the wires. This would be even more severe on
crank up towers, as due to the rigging arrangement, the flexing over the
pulleys normally takes place in two directions, thus bending the wire
back and forward through 180 degrees.

It is not often appreciated that the pulley has to fit the wire exactly.
If the wire is too big the wire suffers abrasion from the side of the
pulley. If the wire is too small, it tends to flatten out in the trough
of the pulley.

If the galvanised wire is correctly sized for the spools, properly
installed, maintained and not subjected to overload. Then the
manufacturer of the tower is using the correct material, which should
give many years service.

I only change my crank up tower wire every ten years, but I do have a
rigid maintenance policy. I lubricate the wire twice a year with
motorcycle chain lubricant. It is available in pressurised cans and is
designed to penetrate and exclude water. I ensure that for the first few
weeks after installing a new wire, the spooling on the winch drum is
carefully watched and if need be assisted to lie correctly on the drum.
I always retain a load on the wire to exclude water and I also check for
any broken wires. Any more than three broken wires and the wire rope
would be condemned.

Stick with the wire rope recommended by the tower manufacturer. Carry
out regular maintenance and you should never experience a failure.

73 John
-- 
John Cramond - GM4NHI
<john@gm4nhi.demon.co.uk>
Home Page - X7/MA5B/SSTV Reviews: www.gm4nhi.demon.co.uk

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