[TowerTalk] Middle Bearing Plate; was Rohn 45 Question

[john at kk9a.com]

Is the aluminum on the rotator side of the mast or the top?   Hopefully the 
Chromemolly is on the bottom.  If the 6' piece in the tower is bowing, the 
24' sticking out of the tower must really be bowing.   You could minimize 
this by using a 3" mast.

John KK9A


To: <towertalk at contesting.com>
Subject: [TowerTalk] Middle Bearing Plate; was Rohn 45 Question
From: "Doug Rehman" <rehman at surveil.com>
Date: Sun, 26 Aug 2007 12:53:59 -0400
List-post: <mailto:towertalk at contesting.com>

An extreme real world example that might support the idea of using a second
thrust bearing/bearing plate:

My tower is a Tri-Ex (Tashjian) LM-354HDSP crank-up/tilt-over. My mast is
30' (18' CM + 12' aluminum) with 6' in the tower. (Before anyone asks, yes I
did analysis and the load I have on the tower is acceptable.) The Tri-Ex
rotator plate sits on top of the braces. It is not held by anything other
than gravity when the tower is vertical; I have stabilized it somewhat when
the tower is horizontal by placing compression clamps on the tower legs
immediately above the rotator shelf.

When the tower is horizontal, there is a quite noticeable bow in the CM mast
between the rotator (Yaesu 1000) and the thrust bearing at the top of the
tower. I can imagine that this same bowing happens when the tower is
vertical and the stack is being pressed by the wind. A second bearing
between the rotator and the top bearing should eliminate (or at least
minimize) this lateral force on the rotator.

I've already got the second shelf and second thrust bearing; I'll probably
install it in the not too distant future.

BTW, the Tri-Ex thrust bearing at the tower top has a grease zerk.

Doug
K4AC