[TowerTalk] Thrust bearing question.

[Jon Pearl - W4ABC]

Hello group.



I've got a question about a future configuration and thought to ask your 
opinion.

I've got a US Towers TX-455 that I'm about to purchase a new M2 OR2800 
for.  I called US Towers and asked what they offer in the way of a 
bearing plate to be situated just above the rotator. Apparently, they 
/don't/ offer a bearing plate.  Their plate that is designed for 
rotators isn't meant to mount a bearing due to the way it's 
manufactured.  Their concern with using their rotator plate as a bearing 
plate centers around the fact that the plate doesn't permanently attach 
to the tower, but merely sits down inside of it, held in place by the 
three horizontal members (rungs) that it rests against - thus making for 
a situation where side loads placed on the plate could be transferred to 
one of the three (or all three) of the rungs - possibly bending them.

Okay... I guess I can see that.

Next, I called M2 and asked what I should do to promote a long life and 
prevent damage to their rotator with it mounted inside of TX-455 top 
section.  Their answer, "Just use a thrust bearing."

The TX-455 top section is flat.  That's where the thrust bearing 
goes.... on the very top of the tower.  Several inches below it is 
another flat plate that's also welded into the tower.  Between the top 
plate and the plate down below it is a center tube that's welded between 
them that the 2" mast will ride in.

With a 21' long,  2" O.D. 1026 DOM tube projecting 16' out of the top of 
this tower - what possible protection could a thrust bearing at the very 
top of the tower offer the rotator more than five feet down, inside the 
tower?  I'm concerned about with the side loads on the rotator head 
created by wind forces on the mast and antennas above the fulcrum.

Is my thinking wrong on this?  Shouldn't I try to mitigate the side 
thrust on the rotator head, just above it?


What say you?



73,


Jon Pearl - W4ABC
www.w4abc.com