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[TowerTalk] Long Masts -- Intermediate Bearing?

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Subject: [TowerTalk] Long Masts -- Intermediate Bearing?
From: (Stan Griffiths)
Date: Mon, 6 Apr 1998 00:53:12 -0700 (PDT)
>When using a long mast (say 20 ft) in a flat top section of 45G where a
>thrust bearing is installed on the flat top and the rotor is mounted about 5
>feet down inside the tower....  what is the preferred method of
>supporting/guiding the mast between the rotor and the top of the tower:
>(1) Do nothing?
>(2) Fab up a tube/sleeve slightly larger I.D. than the mast O.D. and pass
>the mast through it? If this is your preference how do you design the sleeve
>support... weld it on the bottom of a Rohn accessory shlef? What do you use
>for sleeve?
>(3) Install an intermediate thrust bearing? How do you mount... on a Rohn
>accessory shelf? I see in the Texas Tower's catalog that rotor plates are
>not designed to substitute for a flat top (rotor plates flex).... but is
>this a problem on an intermediate bearing?
>I would think some sort of support is needed inside the tower at least on a
>temporary basis if one plans to use a tram to raise an antenna and the tram
>is attached to the mast. Without such a support all the pull is on the top
>bearing and it would seem the bottom of the mast would go all over the place
>(and bearing would seem to be under undue stress). Other ideas for tramming
>if (1), (2) or (3) not used? 
>Larry WI5A
>Friendswood, TX

Hi Larry,

I think the use of a pipe top (45AG3) rather than a flat top should solve
all those problems.  If you really need a thrust bearing, it can be mounted
on a rotator shelf.  True, they aren't very thick but I have not seen one
fail in that application.


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