[TowerTalk] Re: Thrust Bearing Usage

[David Robbins K1TTT]

> 
> I've been monitoring this interesting thread. I haven't had the need
to
> replace a rotor (yet) and I only have one thrust bearing on the top
(flat)
> plate. The rotor is 4 feet down the tower with the rest of the 20 foot
C-M
> mast and two beams above. It seems to me that if you lift the mast out
of
> the rotor and clamp it above the bearing, it will very much want to
sway
> and
> tilt with the better part of the weight above the tower. It seems you
> would
> have to do some sort of stabilization just above the rotor to have a
> fighting chance - a sort of faux bearing. Am I reading this correctly
or
> is
> my physics off ?
>

Your physics is fine, 16' above the bearing and 4' below with all the
weight above will definitely want to tip over.  To keep it from tipping
a real bearing does the job also.  You can rig it temporarily by tying a
very tight wire or rope loop as low in the mast as you can around each
tower leg.  3 separate tight loops do a decent job of holding it upright
while the rotor is replaced.  Note, don't take a shortcut and just loop
around a leg then loop around the next leg without tying it off on each
one or vibration will cause it to work its way off to one side or
another making it very hard to get back straight.

On my flat tops I always put a second bearing just for that purpose
above the rotor.  To keep it from binding I leave it loose until needed
to remove the rotor.  And I do let the top bearing carry the weight of
the mast and antenna(s) and leave that 1/4" or so gap below the mast so
its easy to remove the rotor when needed without jacking up the mast.


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
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