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Re: [TowerTalk] Replacement Thrust Bearing

To: K7LXC@aol.com, towertalk@contesting.com, k6uj@pacbell.net
Subject: Re: [TowerTalk] Replacement Thrust Bearing
From: TexasRF--- via TowerTalk <towertalk@contesting.com>
Reply-to: TexasRF@aol.com
Date: Fri, 17 Apr 2015 20:10:30 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hi Steve, one solution to the set screw limitations is use of a shaft  
collar. They are made in three flavors, solid with a single allen head set  
screw (often 3/8" or 1/2"), single slot with one or two allen head screws to  
pull the slot closed and tightly grip the shaft and with two slots and four  
allen head screws that allow installation without removing the shaft from the 
 bearing.
 
You can get them from Graingers, McMaster Carr or most any bearing  house.
 
They are available made from steel (they will rust), cad plated steel  
(takes longer to rust), nickel plated steel (takes much longer to rust and also 
 
aluminum.
 
For added security, two collars (or more) can be stacked. 
 
The weight will be transferred to the bearing bore sleeve and the bearing  
set screw or locking collar only keeps the mast centered. That is about all 
they  are good for anyway.
 
The issue of a rusting bearing set screw can be eliminated by using a  
stainless steel set screw which are available at the same firms as above as 
well 
 as Home Depot, Lowes and better hardware stores.
 
I have used this solution on some very large and heavy EME antennas  
weighing as much as 2000 pounds. I have substituted the allen head set screws  
with short stainless steel bolts on some to allow use of a box end wrench to 
get  the set screws really tight and more easily removed if need be.
 
Bearings are available with nickel plating but the cost is way more than I  
want to pay. As someone suggested earlier, some paint and a rain shield 
will  work quite well to preserve the bearing. I think the main precaution is 
keeping  rain from washing out the grease which could allow the bearing to 
rust.
 
73,
Gerald K5GW
 
 
 
 
 
 
 
 
In a message dated 4/17/2015 4:56:23 P.M. Central Daylight Time,  
towertalk@contesting.com writes:

>  I am overhauling my rotator and thought it would be  good  to replace my 
thrust bearing also.
I have the Rohn TB3  bearing now.  It  has been in use for 18 years and 
feels pretty  rough.

That's pretty SOP for a mature TB3. What are   you using the tb for? If 
you've got all of your mast and antenna on  it  taking the weight off of 
the 
rotator, that's one thing. If you're  just using it  as a bushing to help 
with horizontal forces, that's  another. 

With case 1, another bearing might  be the way to  go. The rough races 
will only get rougher (steel ball  bearings in an aluminum  race will only 
take so much  abuse).

With case 2, it's probably FB since you're  not  asking it to do much. 

>  Im thinking of going with a  different bearing this time with a steel  
body and greased. (grease  fitting)  
Looked thru the archives on tower  talk to find out  what others have used 
and can?t find much,
on this type of   replacement and I know the bearing supply houses have 
them, just  haven?t  
pursued searching with them yet.   I would like to  know what  others have 
used.

I haven't seen a  decent bearing like you're  describing that'll work 
outdoors. US  Tower uses a pillow bearing that's designed  for indoor use. 
There's  an Allen screw that holds everything and over time the  Allen 
screw  
rusts terminally and you have to drill it out to do anything with   the 
bearing 
or mast. Not recommended. 

>   Array  Solutions has their model TB2 which is this type of  bearing but 
it  only has a two hole flange for mounting.  

Again,  even if you have the bearing holding the  weight, you're still 
not  asking it to do much. I don't see any way to secure the  mast from the 
 
picture. If it's got the aforementioned Allen screw, you could be   screwed 
as 
well. 

IMO thrust bearings are only  marginally useful  since you want some/all 
of the mast/antenna weight  on the rotator or just have  it act as a 
bushing 
so you might rethink  the TB issue and whether you even  need one.  

Cheers,
Steve    K7LXC
TOWER  TECH
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