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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