[TowerTalk] US Tower bearings ?

[K7LXC at aol.com]

In a message dated 4/27/2010 10:15:42 A.M. Pacific Daylight Time,  
towertalk-request at contesting.com writes:

>  I just took possession of a used US Tower Corp HDX-689  yesterday.  
What's the deal on the
2 x thrust bearings?    Mine are both for a 2" mast.   What I DON'T see 
is.. any set screws,  etc
for either of the bearings.  [these are US-tower corp  bearings].    I slid 
a piece of 2" OD AL 
tubing I had handy..  and it slides right through the bearings.. then into 
the K7NV prop  pitch
clamp... also made for a 2" mast. 

>  The ID  of  BOTH  bearings appears to be 2  1/16".     So there  is a 
1/32"  [.03125"]  gap between 
mast ..and ID of  bearings.    So there is a little ..'play'  in it.    Why 
no  set screws ?? 
I was thinking of stuffing a   .030"   or a .027"  thick shim in there.. to 
take out the  play.  


    No, the top part of the bearing is a little  eccentric. You turn the 
top collar until it's snug and then tighten the little  Allen screw. 
 
    It's one of my least favorite thrust bearings.  The Allen screw WILL 
rust and then you'll need to drill it out in order to  remove the mast or do 
anything else with the mast. 

>   OK,  with NO set screws on either thrust bearing... the ENTIRE weight 
of  mast + yagi's, etc..as is, will  be sitting on the prop pitch. 
 
    Which is fine with the prop pitch. All rotators  should have some 
preload on them to seat the bearings. The Orion 2800 wants  ALL the weight on the 
rotator. It doesn't hurt with any other others either.  

Which means the purpose of the thrust bearing is  to really hold the 
HORIZONTAL wind forces which you can do with a bushing or  even a piece of wood. 
IMO thrust bearings are highly over-rated.
 
Cheers,
Steve     K7LXC
TOWER TECH -
Professional tower services for hams
Cell: 206-890-4188