I used a self-centering industrial bearing at the top of my tower, similar
to: http://www.applied.com/catalog/ma/catalog.do?e=10&s=2000776&r=0 . I lube
it once each year with marine grease. It cost about what a TB-3 would cost
($70 in 2001.) Because it's self-centering, it will accommodate up to a +/- 2
degree misalignment of the mast and bearing centerlines. FWIW.
Gene Smar AD3F
-------------- Original message ----------------------
From: "K8RI on Tower talk" <email@example.com>
> 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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