Dino,
Sorry, but I totally disagree. Perhaps we have a misunderstanding of
terminology here? Let's take it from the top and go through the entire
scenario.
The U-bolts are on the top casting of the rotor. They hold together the
two pieces of the rotor's mast clamp. The U-bolts themselves do not
slip. But if they aren't tight enough (or strong enough to withstand
being tightened enough), the mast can slip in the rotor.
The Slipp-Nott is mounted on the mast above the rotor. It is designed to
do a much better job of gripping the mast than does the rotor's mast
clamp. It does this by having much more surface area in contact with the
mast than does the rotor's mast clamp. It also is coated with a material
intended to increase the coefficient of friction between the mast and
the Slipp-Nott.
Up to this point, this is a great concept. But consider what happens
next. The Slipp-Nott has a great grip on the mast. The rotor has a
not-so-great grip on the mast. To be effective, the Slipp-Nott needs to
be solidly connected to the rotor, so that there is no rotation of the
Slipp-Nott relative to the rotor.
How do they do this? They have a pair of thick brackets connecting the
Slipp-Nott to the rotor. The brackets are attached to the Slipp-Nott by
a pair of 3/8-16 bolts. The brackets are attached to the rotor by the
Rotor's U-bolts. In the case of the HAM series rotors, these U-bolts are
1/4-20.
Assume the clamping portion of the Slip-Nott is working as intended,
that is there is no slippage between the mast and the Slipp-Nott clamp.
Now you get a high wind condition, sufficient to cause the mast to try
to rotate. If it slips at all in the rotor clamp, which we know it has
done in the past or we wouldn't be adding the Slipp-Nott, the only thing
limiting this slippage is the strength of the brackets connecting the
Slipp-Nott clamp to the rotor top casting. And what is now the weak link
in this chain? The strength of the 1/4-20 rotor U-bolts which are
holding these brackets to the rotor top casting! And as I said, if this
U-bolt fails, which is what happened to me, you have gone from the
annoyance of an antenna which is misaligned with the rotor to the big
problem of an antenna which is now free-wheeling in the wind.
I have a couple of other comments, so please read on.
After the experiment I reported on here a couple of months back, where I
determined that the 1/4-20 U-bolts just aren't strong enough to prevent
mast slippage, I came up with a different solution which I hope will
prove to be effective over time. I bought a 3 1/2" galvanized saddle
clamp from Cycle 24 Antennas, their part #CL3500.
http://www.cycle-24.com/u-bolt-saddle-clamps/u-bolt-saddle-clamps-for-3-5-inch-tubing/
This clamp is large enough to go around the entire mast clamp assembly
on the upper casting of a HAM series rotor. It provides much additional
clamping force on the mast without modifying the basic design of the clamp.
Time will tell whether this is the solution I was looking for.
Alternatively, I could have drilled and pinned the assembly, but I
didn't want to need to take it down and I didn't think it was advisable
to try to do it at the top of the tower.
I know there are those who maintain that a HAM series rotor is too small
for a KT-34XA. All I can say is that I've been using this combination
for over 32 years and have never experiences a rotor failure. The only
problem I have had is this occasional mast slippage. And until about 10
years ago, the mast had NEVER slipped, I and have belatedly figured out
why that is.
When I first put up my tower in 1970, I was only two years out of
college, I had just bought a house and I had just gotten married. In
other words, I had limited funds to invest in an antenna system. I put
up a TH6-DXX with the HAM series rotor, and used a somewhat rusty
section of 1 1/2" (~2" OD) water pipe for a mast. The antenna was only 2
feet above the thrust bearing, so I didn't think I needed anything
better for a mast. In 1981, I replaced the TH6-DXX with the KT-34XA, but
continued to use the rusty mast. I never had a slippage problem until I
replaced the rusty mast with a shiny new one about 10 years ago, so the
KT-34XA had been up on the rusty mast for 22 years without slippage. I
have come to the conclusion that the rusty mast was providing much more
friction to the mast clamp than I got with the smooth and shiny replacement.
Merry Christmas and Season's Greetings to all TowerTalkers!
73,
John, K9MM
Dino Darling wrote:
Its just the opposite. Its intended to transfer the force FROM the
slipping u-bolts TO the Slipp-Nott.
Dino - KX6D
-------- Original Message --------
Subject: Re: [TowerTalk] Slipp-Nott
From: John Becker <johnb3030@comcast.net>
Date: Sat, December 21, 2013 10:06 am
To: towertalk@contesting.com
I see nothing wrong with the slipp-nott design if used with enough
rotator. Unfortunately many rotators depend on the mast slipping to
protect the rotator.
73,
Roger (K8RI)
The problem I see with the design is that it transfers the force to the
U-bolts, which are not intended to withstand that. They may hold if they
are large enough, but I feel it still is a misapplication, a case of
using something in a manner for which it was not intended by the
original designer. Also to be considered is the fact that if a U-bolt
fails you have gone from an annoyance to a big problem.
73,
John, K9MM
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