[TowerTalk] Thrust Bearing adjustment

Roger (K8RI) on TT K8RI-on-TowerTalk at tm.net
Thu Apr 10 18:36:02 EDT 2014

On 4/10/2014 5:45 PM, john at kk9a.com wrote:
> The top bearing should hold the vertical load.  I use the rotator bearing to
> stabilize the mast vertically. Why do you need a second TB2US?

Depending on spacing and load arm, the top bearing can serve as a pivot 
applying considerable lateral load to the rotator.

It is almost impossible to divide the vertical load equally, or even 
nearly so.  Too many variables to keep it that way if you could achieve 
it initially.

As a rule of thumb, I use "the second, or lower bearing should be at 
least twice the distance from the top bearing as the top antennas are 
from the top bearing".

The bottom bearing should not be tight enough to hold vertical load. 
Just close fitting enough to limit side motion. I use the bottom bearing 
to hold the mast when removing the rotator.

Without the rotator and only the top bearing the lateral twisting moment 
on the bearing can be enough to easily destroy the one bearing.


Roger (K8RI)

> John KK9A
> [TowerTalk] Thrust Bearing adjustment
> from [Mike Fahmie]	[Permanent Link][Original]
> To:	 Tower Talk <towertalk at contesting.com>
> Subject:	 [TowerTalk] Thrust Bearing adjustment
> From:	 Mike Fahmie <wa6zty at yahoo.com>
> Reply-to:	 Mike Fahmie <wa6zty at yahoo.com>
> Date:	 Thu, 10 Apr 2014 13:46:43 -0700 (PDT)
> I'm about to raise a 72' US Tower equipped with a pair of TB2US thrust
> bearings
> spaced about 3'.  I'll be using a TailTwister2 Rotator.  Is there a
> procedure
> for centering these components to preclude binding?
> I doubt there is a way to make the two bearings share the vertical load, so
> which one should I choose.  I'm thinking that the top bearing should take
> the
> load and use the lower bearing to stabilize the mast laterally.
> -Mike-
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