Wow, than you for this great summary on the subject and research Grant!
It sure makes all the sense that clips too far apart will be less effective due
to the possible slack. Though not saddling the dead horse and having the first
clip close to thimble seem more important also in the Crosby material.
73
Tonno
ES5TV
-----Original Message-----
From: Grant Saviers [mailto:grants2@pacbell.net]
Sent: Tuesday, September 12, 2017 8:24 PM
To: Tonno Vahk <tonno.vahk@gmail.com>; towertalk@contesting.com
Subject: Re: [TowerTalk] Turnbuckles with Rod Sides
Tonno,
Glad to hear your beautiful tower is ok!
I did a little reading investigation about the mechanics of wire rope clip
spacing and found it is pretty complicated. The basic idea is to
have the clips more or less share the load forces. With the clips far
apart there is slack between them that makes the up the guy ones less or even
not effective.
The close spacing to the thimble is desired so the thimble can not be upset
from side or reversing forces that would cause the wire to jump out of the
groove. Additionally, for guys a heavier gauge steel is used in the thimble so
it does not deform on the pin. Having the right diameter pin inside the thimble
also reduces the stress on the thimble.
It is also possible to get thimbles with a cage near the jaw end that prevents
the wire from twisting out. Wire rope is specified for a minimum bend radius
since the outer fibers in a bend have more stress.
This is very important when repeatedly going over sheaves, less so for once in
a thimble, but correct size strong thimbles are important to reduce that stress
differential.
Each size clip and wire rope type has a recommended tightening torque so a
torque wrench is strongly advised for tightening and not over tightening. I've
also found it is best to re-torque after a day or two as the stresses in the
wire and clip redistribute. It is hard to hold the saddle when tightening so
as to not over bend the wire. Even with everything done to "spec" most clip
terminations won't hold to the wire rope breaking strength. Hence, other
terminating systems are much more common for cables made to size. Most common
are swaged fittings such as used on sailboat rigging and some tapered sockets
when the termination must be done in the field.
A lot of data is in the Crosby catalog for all sorts of terminations and
rigging. In the US they are pretty much recognized as the gold standard of
rigging quality. Their prices are equal to their reputation, but considering
the small extra cost versus what a tower system like yours costs, their stuff
is very cheap insurance monetarily and for life safety. No affiliation, I'm
just a happy customer.
The Crosby catalog https://www.thecrosbygroup.com/catalog/
The Crosby Wire Rope Terminations User's Manual
https://www.thecrosbygroup.com/wp-content/uploads/2014/01/9992320_Termination_Manual_With_Cover_LoRes.pdf
(The clip info is near the end.)
I hope this is helpful,
Grant KZ1W
On 9/12/2017 4:55 AM, Tonno Vahk wrote:
Oh, hold on guys!:) The 15m array is still up and running! Good way to get
those rumors going:) I did lose another 45m rotating tower 2-3 years ago though
due to the turnbuckle failure. The tower went back up last autumn with new
antennas. It was a painful lesson and certainly I am using safety wires on all
my turnbuckles now!
I did learn about the saddling of the dead horse thing and have fixed the wire
rope clips. The only thing that I am probably not doing right is the distance
between wire rope clips on the wire. Given I had quite long ends of the wire
left over I left also half a meter or more between
4 wire rope clips (the first one right after the thimble).
Is it and why is it crucial to keep the wire rope clip close to each other on
the wire (2" or so)?
73
Tonno
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