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Re: [TowerTalk] Thrust bearing shot

To: "K8RI on Tower talk" <>
Subject: Re: [TowerTalk] Thrust bearing shot
From: Dino Darling <>
Date: Fri, 12 May 2006 16:25:06 -0700
List-post: <>
Hey Roger!  I can't wait for the new set of 
pictures to be uploaded to your antenna web site!

Your old bearings are designed for radial loads 
only (I know, Dino is preaching to the choir 
again).  I know this has been beaten to death out here.

Some day I'll sit down and design a case that 
will accept a readily available and replaceable 
Timken bearing and seal.  If you go to 
McMaster-Carr's web site and punch this page 
number into the search field, you can read about 
the bearings I'm talking about....
Page: 1056
P/N  : 5709K32  (2" ID Bearing)
P/N  : 5709K68  (Race)
Dynamic Load:
     Radial = 8,270 LBS
     Thrust = 4,710 LBS

>Steel Tapered-Roller Bearings:
>Also known as Timken bearings, tapered-roller 
>bearings handle both radial and thrust loads, so 
>you can use them virtually anywhere wheels and 
>shafts turn. The two-piece design offers 
>excellent strength, high load capacity, and long 
>life. A complete bearing consists of an inner 
>ring and roller assembly plus an outer ring 
>(sold separately). All components are made of 
>steel. Made to Class 2 tolerances. Temperature range is -65° to +200°  F.

An old trailer hub w/ a single bearing and a 
little machining could be used too.  Bolt the hub 
to the tower face down with the right seal and 
you would never have to replace a bearing assembly ever again!


At 03:33 PM 05/12/2006, K8RI on Tower talk wrote:

>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

Dino - K6RIX 

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