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Rotating Tower Sections

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Subject: Rotating Tower Sections
From: (Robin E. Midgett)
Date: Sun, 6 Oct 1996 14:37:30 -0500 (CDT)
        Hello Steve,
        Thanks for your reply; what you suggest sounds very interesting. I
had not thought of doing it that way. Essentially, you are suggesting a
heavy duty mast to serve as the backbone of the climable mast. It seem to me
that would work out just fine provided that the mast is of sufficient stock,
& I know there are masts on the market adequate to handle the job. The 'Lazy
Susan' approach I have been considering relies on the strength of the steel
plates it is made from & the cam followers which would be used to keep the
plates one on top of the other & aligned. BTW, I had planned to have
whatever I fabricated hot dip galvanized to guard against the elements.
        I think a 12' mast is not necessary; probably a 8' mast will serve
nicely, & that lets me fit the 25G down over it w/ no problem. One could
probably hoist the 25G & mast up as an assembly, lowering them down into the
45G. An accessory shelf should serve nicely in conjunction with some
galvanized angle & SS or galvanized  u-bolts to center the 25G. What do you
think, a 3" mast w/ 1/4" walls? Perhaps 3/8" walls, or 1/2"?
        The only real snag I see at this point is having enough space inside
the 45G to get my rotator in & out. I plan to use a prop pitch motor inside
the tower; with 4' of mast down inside the tower, I may be too far down to
use the holes(wide crossmember spacing) provided for rotor
installation/removal. I may have to outboard the prop pitch.

At 10:37 AM 10/6/96 -0400, you wrote:
>In a message dated 96-10-06 00:38:58 EDT, you write:
>>    I am interested in rotating 1 or 2 sections of Rohn 25G (stacked
>>vertically, in the normal manner) on top of 130' of Rohn 45G, which will
>>remain stationary. My basic plan is to build an industrial size "Lazy
>>Susan". I would like to hear from anyone who has experience in this area so
>>as to gather more information & ideas. The 45 has the flat top section on
>>it, which will serve as the base for the 25.
>Hi, Rob --
>    Here's scheme that I like but confess have never tried myself.  The top
>of the 45G has a flat plate and TB-4 (3 inch) thrust bearing.  It also has an
>accessory shelf with another TB-4 on it below the top of the tower in
>addition to the accessory shelf below it with the rotator.  Install a
>suitable 3 inch mast so that half of it is installed in the tower and half is
>sticking out.  You'd probably need a mast at least 12 feet long (six feet
>below and six feet above).
>     Now you invert a flat 25G top section with another TB-4 on it and
>install it over the mast sticking out. This will sit the 25G flat top plate
>on the top of the TB-4 on the 45G.  (The thrust bearing on the 25G is just to
>hold it in place and centered.  If you can figure out a way to center the 25G
>and hold it securely, you could skip this TB-4; perhaps the angle iron +
>U-bolt approach.)  Now you need a method to fix the mast to the top 25G tower
>section.  You can probably use a 25G accessory shelf with a piece of angle
>iron attached to it with a 3 inch U-bolt through the angle iron and around
>the mast to secure it.  The trickiest part of this installation is lifting
>the 25G over the mast.  A regular Rohn ginpole doesn't have enough overhead
>to do this with its 12 foot mast.
>    I would recommend this approach rather than a 'fabricate it yourself'
>method because 1) you're using standard parts and 2) they are designed for
>outdoor use.  Anything that is fabricated should be hot dipped galvanized at
>a minimum.  The only fabricating you have to do with this scheme is
>installing the angle iron piece and the U-bolt.
>>        BTW, I have talked to Dick Weber of RTS & am aware of his fine
>>products; I am looking for a more economical solution. I plan to assemble an
>>array of VHF/UHF antennas on this climbable mast once it is in place. 
>     While I respect Dick and his products, everyone is looking for a more
>economical solution.  With your relatively small antenna system, the 25G
>should be okay.  Otherwise, I would go with 45G up  above as well.
>73 and good luck,  Steve   K7LXC
>    TOWER TECH - - professional tower supplies and services for amateurs
73, Robin KB4IDC

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