> Roger:
>
> 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.
I've thought of those as well as taper bearings (like a wheel bearing of the
proper size but with both races)
In that case you do have to cut inner and outer retaining rings though.
My big problem with any real bearing it getting it in place. It's nigh onto
30 feet up to the top of the mast which is quite a reach. I'd basically
have to lower the mast down into the tower, unclamp the antennas (one by
one?), remove the TB-3, and then install the new one in reverse order. I do
have to replace the pig-tails (28' each) which means letting the mast down
any way. We do have an industrial bearing and fastener supply locally so I
might be able to find one of those self centering ones.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
>
> 73 de
> Gene Smar AD3F
>
>
> -------------- Original message ----------------------
> From: "K8RI on Tower talk" <k8ri-tower@charter.net>
>> 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
>> www.rogerhalstead.com
>>
>> _______________________________________________
>>
>>
>>
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>
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