[TowerTalk] One thrust bearing vs. two

[john at kk9a.com]

I have never heard of a rotator mounted inside a tower with only one bearing 
breaking due to lateral force.  Has anyone ever seen this?

John KK9A


----- Original Message ----- 
From: "Tod -ID" <tod at k0to.us>
To: <john at kk9a.com>
Cc: "'Tower Forum'" <towertalk at contesting.com>
Sent: Wednesday, August 12, 2009 1:27 PM
Subject: RE: [TowerTalk] One thrust bearing vs. two


Hi John:

Yes, proper alignment can be a challenge. The rotator plate is welded into 
my
tower at 4 feet down from the top. The objective of the second bearing 
seemed to
me to be to prevent lateral motion of the mast when the wind is really 
pushing
on it and the antennas.

I thought about calculating the moment at the top bearing when the wind is
blowing and then calculating what the lateral force on the rotator would be. 
I
am not sure if they are specified for lateral forces -- they do have a spec 
for
vertical forces.

It could be that inserting a plate with no bearing that had a hole slightly
larger than the mast o.d. would sufficient to protect the rotator.

Tod, K0TO


> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of john at kk9a.com
> Sent: Wednesday, August 12, 2009 8:44 AM
> To: towertalk at contesting.com
> Cc: tod at k0to.us
> Subject: Re: [TowerTalk] One thrust bearing vs. two
>
> Tower top plates and rotator plates are not manufactured very
> precisely and trying to line up two bearings plus your
> rotator bearing could be difficult. If it's not lined up
> exactly it will cause some binding and add more stress to
> your rotator and I don't see any benefit to having a lower
> bearing if you are using an adequate rotator.   I think just
> using a top bearing and a heavy duty rotator about 5' or more
> below would be a better choice.
>
> John KK9A
>
>
> To:  "'Tower Forum'" <towertalk at contesting.com>
> Subject:  [TowerTalk] One thrust bearing vs. two
> From:  "Tod -ID"
> Date:  Tue, 11 Aug 2009 22:20:15 -0600
>
>
> I would be interested in 'opinions' on the need or utility
> for only one thrust bearing at the top of a tower vs. two
> thrust bearings one at the top and the other several feet
> below the first.
>
> Tod, K0TO
>
>
>
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