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@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@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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|