## I forgot to add that the lower bearing comes into play when mast is raised
a bit..and rotor is out. At that point, I use the locking ring on the lower
bearing. I also use a spare OR-2800 mast clamp and clamp around the chromolly
mast. This ensures the weight is on the lower bearing. Of course b4 u raise
the mast a foot, the top bearings ecentric collar must be loosened..... then
retightened after mast goes up 1 foot.
I would not recommend not using the lower bearing at all....and only relying
on the gaping hole in the lower bearing plate. In most cases its too much
slop. Some have also used a sheet of .5 to 1.0 inch thick UHMW with a 2 or
3 inch hole in it. Hole is bige enough to not bind... but still allows to
restarin the mast in the lateral direction. Then u can still use a u clamp or
spare or-2800 mast clamp, dx eng super clamp etc.. on the hb uhmw bearing...to
take the weight.... while doing rotor repairs.
Jim VE7RF
Jim is right on the money. The second bearing in the middle is loose all the
time until you need it to hold the bottom of the mast after raising the mast
off the rotator for a rotator fix.
When I put in my Tri-Ex LM-470 I took the existing rotator plate and put it
inside my Duplicator™ machine. After inserting 50 cents and pressing the start
button I had an exact duplicate. Both rotator plates went into the tower, the
lower one for the rotator (about 3-4' down) and the second one between the top
and the rotator. I built a mast raising fixture/winch on the second rotator
plate to raise and lower the mast on the tower and for future rotator service.
It works great! Rather than using a bearing on that plate, I used four small
pieces of HDPE plastic with radiused ends to match the diameter of the mast,
used as sliders. After the install was complete the raising fixture/winch was
removed along with the plastic sliders...now it is just an empty plate with a
large hole in the middle of it.
The important thing here is this has to be considered at the beginning of the
project! You can't get the second rotor plate in there once everything is in
place. (Unless you have a crane come in and hold up the entire antenna array
while you put the second plate in there.)
Chris
KF7P
On Apr 10, 2014, at 17:40 , Jim Thomson wrote:
Date: Thu, 10 Apr 2014 13:46:43 -0700 (PDT)
From: Mike Fahmie <wa6zty@yahoo.com>
To: Tower Talk <towertalk@contesting.com>
Subject: [TowerTalk] Thrust Bearing adjustment
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-
WA6ZTY
## DON’T use the set screws in the 2nd ..lower TB2US. I use two of the
same bearings on my UST-HDX-689. Lower bearing is 4 foot down from the top.
PP rotor is 6 foot down from the very top. 2 foot between
lower bearing and rotor. The tb2us uses an eliptical locking ring. It will
either lock CW..or CCW. Just make sure u know which way it went on. A
small recessed partial hole on the locking collare is whacked with a drift
punch..to lock the ring.
## so leave the bottom bearing loose....so it only takes the lateral
load..that’s it. You can only ever line up 2 things...not 3. So with the 2
bearings + rotor.... it becomes the top bearing and rotor...never the middle
bearing. And I sure as hell would not rely on that top double plate and
cylinder on the UST towers to take all the load...esp when rotor removed..mast
elevated a bit...and only the top bearing used. Not with
a 20 ft mast.... with 14 ft above the tower..and 6 foot into the tower.
Which becomes 15 ft above and 5 ft below..when rotor is removed. The double
plate at the top of the tower and cylinder has a set screw..used to lock the
mast when rotor is removed. I would supplement that with some temp u bolts
on the mast + angle steel..so the mast doesn’t rotate in a high wind with
rotor removed.
Jim VE7RF
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