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[TowerTalk] Orion rotator application note

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Subject: [TowerTalk] Orion rotator application note
From: (
Date: Fri, 26 Mar 1999 12:56:56 -0500

On Mon, 22 Mar 1999 18:18:19 -0800 dan hearn <>
>During a conversation w Mike a week ago he said that M2 abandoned the 
>donut shock absorber because the bolts loosened and gave trouble.

He told me the same thing when my donut ( BMW vibration dampener) failed
causing $1200 worth of repairs to the tower.

However nothing loosened up in my case, the bolts all sheared off (
probably from torque twisting) causing the mast to kick out and
fracturing 2 legs of 45G with a KLM 40M4 and a CC 204CD hanging over at a
30 degree angle. A scary sight at 160' up.
The rotator was mounted at the bottom of the top section and 2 thrust
bearings were used. 

I dont know if I should try the donut again with aircraft grade bolts,
etc or just hard mount. Bolt expense is a non issue but future damage is!
 The tower has been extended to 180' and I have no particular desire to
climb on a weekly basis to check everything.

Any ideas out there?  How about castle nuts and cotter pins in lieu of
safety wires?

>also said
>that rotator mounting bolt loosening is a frequent problem. They have 
>some commercial rotator systems w drilled head aircraft grade bolts 
>safety wired.
>These are very expensive. He also said they are looking at some sort 
>of sheet
>metal plate with bend up tabs as used on some automobile assemblies. 
>He suggested
>using RTV on the bolt heads rather than Loctite. This can be cut away 
>with a
>knife if removal is necessary. He feels that it is necessary to 
>periodically do
>maintenance tightening of bolts.

I wonder if the grade of the stainless bolts is causing stretching?  I'm
no mechanical engineer but wouldnt a galvanized and hardened steel bolt
be better?? Ive been on many commercial towers and cant ever remember
seeing stainless hardware. Several friends in the 2 way radio and tower
biz refuse to use stainless.

>  I wonder if the different thermal coefficients of aluminum and steel 
>cause some
>of these problems. I like the use of lock washers to accomodate small 
>changes w temperature. Double nutting, as suggested by Steve , is 
>certainly a
>good practice. 

Rohn supplies a lock nut for many of their accessories; does everyone use
them? (-:

73  Carl  KM1H

 73, Dan, N5AR
> wrote:
>> Greetings, TowerTalkians --
>>       Other than a prop pitch, the Orion 2800 is about the best 
>> rotator available but I've run across three Orions in the last 
>couple of
>> months with the same problem. And that is, in spite of having the 
>best and
>> beefiest mast clamp in the world, all three of them had loosened up 
>and the
>> antennas were being turned by the wind. One was a TH11, one was a 
>C-4XL and
>> the other was an M2 2L 75M yagi.
>>        In all cases, the nuts on the long bolts through the mast 
>clamp had
>> loosened up. And all of these nuts were the nylock ones supplied by 
>> factory and also had spring lockwashers. These were both versions - 
>the fine
>> threaded and the coarse threaded ones so they are both subject to 
>the same
>> problem.
>>      While re-tightening them is great, I think it is inevitable 
>that they'll
>> loosen up again. In the case of the 2L 75M, it went through almost 2 
>> before coming loose.
>>      Anyone using this rotator should plan on taking added 
>precautions to
>> prevent this. In my cases, I'm going to double-nut everything. 
>Another option
>> would be to use some Locktite (sorry - I can't remember if it's the 
>blue or
>> red to use). Or do both. In any case, you won't be sorry.
>> Cheers,  Steve   K7LXC
>> --
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