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[TowerTalk] mast weight = a non issue!

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Subject: [TowerTalk] mast weight = a non issue!
From: (Stan Griffiths)
Date: Thu, 17 Apr 1997 12:13:58 -0700 (PDT)
>On 11 Apr 97, <> wrote:
>> Did you know that the very popular ham series of rotors is set up for a 2" OD
>> mast? Think about it - you are moving one side of that clamp only....and this
>> means that if you are committing the towertalkian sin of using 1 1/2" water
>> pipe which has an OD less than 2" you are turning that mast in an oblong
>> orbit! After 25 years of doing this that hit me recently.  Oooooooooops -
>> QFU!
>Close, but no cigar.
>The Hygain rotors (T2X, HAM-X) are designed for a 2 1/16 inch O.D. 
>mast. Anything smaller should be shimmed for on-center rotation. 
>P.S. No, I'm not using shims on my 2 inch O.D. mast
>Barry Kutner, W2UP              Internet:

So with all of this in mind, I could swear that I read somehwhere that at
least SOME HyGain/CDE rotator was designed for exactly 2" masts.  I dug out
my whole library of old and newer rotator manuals (probably 20 manuals for
Ham-M, II, IV, Tailtwister and other smaller rotators) and scoured them for
this info.

What I found was that, with one exception, all of the HyGain/CDE rotators
are specified to take 2 1/16 inch masts and shimming to center the mast in
the center of rotation is strongly recommended.  The exception is rather
interesting in that it occured in a late CDE Tailtwister manual and then
again in an early HyGain Tailtwister manual.  Those manuals CLEARLY state
that the Tailtwister is made for 2" masts (not 2 1/16" masts).  I suspect
this was actually an error in the CDE Tailtwister manual and the error was
merely copied into the HyGain Tailtwister manual when HyGain took over the
product line.  I would bet, though I am not absolutely sure, that the
hardware has not changed and early Tailtwisters use the same castings as
later ones.  The later Tailtwister manuals show the correct mast size for a
Tailtwister to be 2 1/16".  This would certainly explain some of the
confusion, though, wouldn't it?

Here is a tip for an easy way to do the shimming.  I always found that
trying to wrap the mast in a curved piece of sheet metal of the right
thickness was always a pain in the rear.  Instead, it occurred to me that if
I placed two strips of 1/32 inch thick metal right in the two places where
the mast contacts the rotator casting, that this would assure that the mast
was exactly where it was supposed to be.  There is no need to shim under the
U clamps since it does not matter where they are relative to the center of
rotation.  So what I do is cut two 6 inch long by 1 inch wide flat stips of
1/32" aluminum, bend about a half inch over at the top so this bent part
will rest on the top of the rotator casting, slip the "strip shims" in the
right place between the mast and rotator casting, and tighen everything up.

I may have mentioned this tip before, but the order in which you tighten the
hardware makes a BIG difference in whether things want to bind during
rotation or not.  What I do is loosely install both of the rotator U bolts,
all rotator to plate mounting bolts, and plate to tower leg U bolts.  With
the shims in place, the rotator U bolts should be tightened first, this
assuring the rotator is perfectly aligned with the mast.  Next, the rotator
to plate mounting bolts should be tightened thus assuring that plane of the
rotator plate is perfectly flat against the bottom of the rotator.  Last,
the plate to tower leg U bolts should be tightened in the position that the
plate wants to rest in with the other bolts already tight.  It's pretty much
impossible to do this right if the weight of the mast (and antennas) is
resting on the rotator.  Since my installations all use thrust bearings
above the rotators, I don't have the "weight on the rotator" problem.

I know this feels backwards at first with a strong tendency to want to
install the plate first, tighten it up, install the rotator second, tighten
it up, and install the mast last, and tighten it up.  Actually, there is
nothing wrong with assembly in that order if you remember to loosen
everything back up and retighten it all in the order that I have suggested
above, ie:  rotator mast clamps first, rotator mounting bolts second, and
plate mounting U bolts last.

I have heard dozens of stories about the bolts that hold the two halves of
the rotator together falling out and spilling bearing all over the ground.
I think if you install the hardware as I have suggested, you will never have
this problem.  I have never had one come apart on the tower in 26 years of
using several Ham-M, IV, and Tailtwisters.

I also scoured those manuals for any mention of "preloading" the rotator
with weight from above and found no reference to it at all.  At least for
the HyGain series of rotators, this appears to be a non-issue.  I can't say
for any other brand.


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