From: Jon Pearl - W4ABC <jonpearl@tampabay.rr.com>
Subject: Re: [TowerTalk] Thrust bearing question
To: john@kk9a.com
Cc: towertalk@contesting.com
Date: Thursday, February 7, 2013, 8:07 AM
Hi John.
There's nothing wrong with the combination you cite.
At present, my rotator *is* inside the tower where it's been
for more
than twenty years but with no thrust bearing at the top of
the tower.
If I wasn't clear, I'm going to continue with the rotator
placed inside
the top section of tower. My question is simply this;
since the rotator
can take all the weight of the mast and antennas with the
mast not being
collared by the thrust bearing in an attempt to relieve the
rotator of
any of that downward force, what purpose does a thrust
bearing serve at
the very *top* of the tower? And when I say
'collared', a Yaesu type
bearing**(http://tinyurl.com/aa2g59n) has the ability to collar,
utilizing four set screws (bolts) to limit downward movement
by the
mast. US Towers calls for a TB-2 type bearing
(http://tinyurl.com/bj9vykg) to be used which provides
centering and
limits side movement.
And "yes" I understand your argument against the use of a
thrust bearing
placed on a plate just above the rotator. While it
does mitigate side
thrust applied to the rotator head, it also adds some
complexity to the
geometry.
Thanks for your reply.
73,
Jon Pearl - W4ABC
On 2/7/2013 8:00 AM, john@kk9a.com
wrote:
What is wrong with using a bearing at the top of the
tower and mounting
the rotator inside the tower? The rotator has an
internal bearing so the
mast is supported by two points. I have built all of my
towers this way.
Some people add an additional bearing just above the
rotator but in my
opinion it is just a place to bind and serves no
purpose other than it
allows you to remove the rotator for repair.
John KK9A
To: towertalk@contesting.com
Subject: [ TowerTalk] Thrust bearing question.
From: Jon Pearl - W4ABC
<jonpearl@tampabay.rr.com>
Date: Wed, 06 Feb 2013
22:25:47 -0500
Hello group.
I've got a question about a future configuration and
thought to ask your
opinion.
I've got a US Towers TX-455 that I'm about to purchase
a new M2 OR2800
for. I called US Towers and asked what they offer in
the way of a
bearing plate to be situated just above the rotator.
Apparently, they
/don't/ offer a bearing plate. Their plate that is
designed for rotators
isn't meant to mount a bearing due to the way it's
manufactured. Their
concern with using their rotator plate as a bearing
plate centers around
the fact that the plate doesn't permanently attach to
the tower, but
merely sits down inside of it, held in place by the
three horizontal
members (rungs) that it rests against - thus making for
a situation
where side loads placed on the plate could be
transferred to one of the
three (or all three) of the rungs - possibly bending
them.
Okay... I guess I can see that.
Next, I called M2 and asked what I should do to promote
a long life and
prevent damage to their rotator with it mounted inside
of TX-455 top
section. Their answer, "Just use a thrust bearing."
The TX-455 top section is flat. That's where the thrust
bearing goes....
on the very top of the tower. Several inches below it
is another flat
plate that's also welded into the tower. Between the
top plate and the
plate down below it is a center tube that's welded
between them that the
2" mast will ride in.
With a 21' long, 2" O.D. 1026 DOM tube projecting 16'
out of the top of
this tower - what possible protection could a thrust
bearing at the very
top of the tower offer the rotator more than five feet
down, inside the
tower? I'm concerned about with the side loads on the
rotator head
created by wind forces on the mast and antennas above
the fulcrum.
Is my thinking wrong on this? Shouldn't I try to
mitigate the side
thrust on the rotator head, just above it?
What say you?
73,
Jon Pearl - W4ABC
www.w4abc.com
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