[TowerTalk] Slipp-Nott

[John Becker]

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 at comcast.net>
> Date: Sat, December 21, 2013 10:06 am
> To: towertalk at 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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