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[TowerTalk] Thrust bearing shot

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Subject: [TowerTalk] Thrust bearing shot
From: "K8RI on Tower talk" <>
Date: Fri, 12 May 2006 18:33:41 -0400
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I thought I'd pass on some information.

It seems like even with care planning for problems when pushing the limits 
the problems turn up where we don't expect them.

I'm running a 97 foot ROHN 45G.  The tribander is supported just above the 
top of the tower on a 24' long, 2" structural steel tube with 1/4 wall over 
an 1 1/2 tube  with 1/4 inch wall made up of two sections totaling about 44 
feet. So the center section has essentially a 1/2 inch wall, supports the 
TH-5 at 100' while the 7L C3i 6 meter beam at 115' is mounted on the 1 1/2 
pipe right at the top of the 2".  The 144/440 array is 12 feet above the 
6-meter antenna at roughly 127'.

The mast is supported by a TB-3 at the top of the tower with a second TB-3 
about 12 feet below the top of the tower that just keeps the mast centered 
with the rotator (PST-61) mounted at 17' below the top of the tower.

I knew the leverage of the tall mast above the top of the tower would create 
some pretty strong forces at the top of the tower, but after about 4 years 
with lots of severe winds up here, the races in the TB-3 have worn to the 
point where the upper race is setting right down on the washers for the 
mounting bolts.  This is causing the bearing to bind to the point the PST-61 
is unable to turn the mast.

It appears as if I'm going to need to replace the upper bearing with a 
pillow block arrangement of some sort with a fairly close fit.  If it 
weren't for the massive side forces created by the leverage I'd use oil 
soaked hard wood, but I think I'm going to need to get a split block of 
steel or Aluminum machined to fit which will give a large surface area to 
support the side forces without undue wear. I sure could use that milling 
machine I was going to purchase before the market tanked back around the 
turn of the century.

And the day before I was going to order some LMR-600 and fittings for the 
pigtails the price went up. <sheesh>

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2 


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