[TowerTalk] Thrust Bearing adjustment

[Jeff AC0C]

Being a tower rookie, I learned this lesson the hard way, needing to replace 
a rotor and no lower bearing.

Necessity being the mother of invention, it turns out that for a 25G tower 
and a 2" mast, you can use 3 2x4 to serve as a centering method.  There is 
just enough space for each 2x4 to slip between the mast and the inside two 
tower leg verticals.  With all 3 in place, the play is a fraction of an 
inch.  In advance, I put a stop screw into the facing end of each one so 
they would not slip out.  It's not very sexy but it works great.  A pair of 
big-mouth Vice grip clamps were used to prevent mast rotation.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: Jim Thomson
Sent: Thursday, April 10, 2014 8:22 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Thrust Bearing adjustment


##  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 at yahoo.com>
To: Tower Talk <towertalk at 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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