[TowerTalk] Top Bearing Plate for 55G vs Rotor

[Jim Thomson]

Date: Tue, 12 Aug 2014 11:59:54 -0600
From: "Doug Renwick" <ve5ra at sasktel.net>
To: "'Grant Saviers'" <grants2 at pacbell.net>,
<towertalk at contesting.com>, <rthorne at rthorne.net>, "'Don '"
<w7wll at arrl.net>, "'Charlie Gallo'" <Charlie at TheGallos.com>, "'Gary
Jones'" <garyejones at cmaaccess.com>
Subject: Re: [TowerTalk] [Bulk] Re: Top Bearing Plate for 55G vs Rotor
Plate

Here is my take.  A blanket statement  does not fit all situations.  A
middle bearing does have merit.  I cases where a long mast fits inside the
tower or there are stacked antennas on the same mast, a middle bearing will
stop the bending moment in a strong wind.  And a bending moment will be
larger with an aluminum mast.
I put a middle bearing in my towers.  Alignment has not been a problem.  The
middle bearing is loosely fitted so there is some room for motion.  It is
easier to have it there than try and install it later.
Doug

##  agreed.  I always use a middle bearing, like a peer brand or similar.
The trick is to not tighten any set screws, locking collars etc, on the
middle bearing.   However, a clamp, like the m2  OR-2800 mast clamp, can be
installed on the mast, on top of the middle bearing, so the weight is on the middle bearing,
yet the mast  can still deflect a bit on the middle bearing.   With a 20 ft mast, and 6 ft into the
tower , and 14 ft above the tower, u gotta be nuts  not to use a middle bearing. 

##  IF u gotta lift the mast up a bit to get the rotor out, the OR-2800 clamp on the middle bearing
can simply be loosened up.... and slid back down the mast til it touches the middle bearing again. 
The mast can then be locked up so it cant rotate, with 1-2  pieces of angle steel /al..and some u bolts to
both mast and tower leg etc.  

##  UHMW, the white stuff, will rot in the sun from UV, then turn brittle, been there, done that.   My middle
bearing is identical to the top bearing.   Id use a middle bearing, even with very little mast out the top of the tower.
Makes for rotor  servicing a lot easier, and a lot safer overall. 

Jim  VE7RF