[TowerTalk] Turnbuckles with Rod Sides

[Grant Saviers]

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