Chris,
I think you will find that Rohn was only referring to "their" thrust
bearing, the TB-3 family. There are other bearings and bushings used,
and often required, in antenna installations that cheerfully accept
axial as well as radial thrust. Some antenna installations deviate from
the simple tribander-on-a-stick, and an analysis of the forces presented
to the tower/mast/rotator combination might well dictate the use of one
(or two) bearings that are capable of handling the forces. Rohn, Create,
CDR, etc have no way of knowing exactly what your installation entails,
and while it would be foolish to disregard whatever recommendations they
offer in the use of their products, they should not be looked to as the
ultimate authority on YOUR installation.
73,
geo - n4ua
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Chris Pedder
Sent: Wednesday, August 12, 2009 11:20 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] One thrust bearing vs. two
Given that we have established, per Rohn, Create and others, that the
function of thrust bearings is to bear lateral as opposed to vertical
loads, can someone please explain to me what benefit, in normal use,
is conferred by having two, as opposed to one, such bearings?
Chris
At 15:06 12/08/2009, you wrote:
>A second thrust bearing normally allows a safe means to remove the
>rotator (lift the mast and secure using the two thrust
>bearings). That alone is more than enough justification for two
>thrust bearings. I cut up an extra cross beam, drilled holes in this
>"angle iron" for this second/lower thrust bearing and attached the
>angle irons to the legs of the tower with u-clamps. Since the mast
>and upper thrust bearing were already in place, the issue of
>alignment was not a concern. I had pre-placed the second thrust
>bearing on the mast as it was lowered into the rotator (making sure
>the mast wasn't loading the rotator). One of my big gun friends,
>K4TD was very concerned over my plans to only use one thrust bearing
>since a 3-element 40 meter beam is not a small load. I don't normally
>argue with the experts. Ken K5RG
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