I wonder if a workable clamp could be found that mechanically starts out
OK and only goes bad over time as the cheap thin coating corrodes so
that maybe we could find some sort of coating that would preserve the
fitting in an outdoor environment or maybe if really lucky in a marine
or near marine environment. What passes for galvanizing these days is
often a thin zinc plating that gets dinged up when worked with tools
but will corrode quickly even when in like new condition.
Unfortunately, like new, means so little.
Patrick NJ5G
On 6/7/2015 2:56 PM, Donald Chester wrote:
It's tower and antenna season once again.
For tower guying I prefer Big Grips, but for some applications I still use old
fashioned cable clamps, for example, to attach guy wires to ground anchors,
allowing for easy re-adjustment as necessary, months or even years after the
initial installation. Another is for strain insulators and other hardware
whose contour won't allow it to fit snugly against the U-shaped bend of the Big
Grip. An engineer at PLP verified that this has caused failure, particularly
with offshore manufactured strain insulators. He strongly recommended against
using Big Grips for such applications, knowingly discouraging potential sales.
For a recent project I ordered a bag of 3/16" clamps from Rohn through one of their distributors,
under the same part number as listed in the Rohn catalogue. Originally, these were part # 3/16 CCM, but
the Rohn catalogue now lists them as 3/16 CCF. The old style were "malleable", while the new
style are said to be "forged". I have found the newer style to be all but worthless. One
would be better off buying cheap wire rope clips from Ace Hardware.
The older CCM clamps had a deep channel in the body of the saddle, which
positioned the dead end to overlay the live cable under pressure from the
U-bolt, so that all compression was exerted between the two sections of cable.
Instead of a real channel, the newer CCF clamps have four bumps on the body of
the saddle, laid out in a rectangular configuration. The channel formed between
the bumps is too shallow to hold both segments of cable in place so that one
rides on top of the other; the dead end tends to ride over to one side at about
a 45 degree angle, wedging partly against the body of the saddle instead of
pressing 100% against the live cable. In addition, the older clamps had a
series of diagonal grooves at the bottom of the channel, designed to grip the
cable over the full length of the channel. The newer ones have a single
diagonal ridge, which pinches the live cable in exactly the same manner as the
U-bolt does when clamps are installed the wrong way and the U-bolt
b
ears down on the live cable. I did a test run with some newer clamps, a piece
of scrap cable and a come-along. I was able to pull the cable tightly enough to
cause it to slip through three clamps with the nuts firmly tightened. I suspect
this would have been impossible with the older clamps; some piece of hardware
would fail or the cable would break before it would slip through the clamps.
Furthermore, the U-bolts that come with these clamps are no better than the
saddles. The older ones were heavily galvanised, like marine hardware. The
newer ones are merely zinc-plated, just like the aforementioned Ace Hardware
product. About six months ago I used some of the newer clamps for a less
critical application, to attach some pieces of guy cable anchoring the end
insulators of a wire antenna. Now, in little more than half a year, the U-bolt
nuts are completely rusted with no remaining sign of zinc plating at all; in
fact the nuts on these clamps are already rustier than the older ones on a
nearby tower that has been up for more than 30 years.
I called this to the attention of a Rohn engineer, and his only comment was that Rohn
"no longer supports" the use of cable clamps with guy wires; they now solely
recommend Big Grips. He said they only list clamps in the catalogue because they still
occasionally get orders for them. The illustration in the catalogue clearly shows a
picture of the older style clamps, not the junk they sell now.
Does anyone know of a vendor who stocks original style heavily galvanised
clamps similar or identical to the older 3/16CCM? Based on what I paid in 1980
and on-line inflation calculators, these should now run a little over $1.00
apiece.
Don k4kyv
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|