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[TowerTalk] TB-3 Thrust Bearings, side and vertical loads

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Subject: [TowerTalk] TB-3 Thrust Bearings, side and vertical loads
From: "K8RI on TowerTalk" <>
Date: Tue, 5 Dec 2006 02:32:43 -0500
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For those who use the TB-3 and 4 to support much weight, I'll try to get 
some photos up in a day or two.  I had to use BP-Blaster to get the bolts 
out of a TB-3 that hadn't been doing much of anything except sitting there. 
Of course that put oil on the bearings and race way which is supposed to be 
dry.  As everything else was rusty except the aluminum I decided to 
dismantle it.

I removed 31 1/4" ball bearings.  That in itself is an interesting exercise 
as it won't come apart until the last ball comes out of the race. Those 
bearings run in races that are cut on the *sides* of the casting. (inside of 
the base and outside of the top/center piece that holds the mast) A race 
like that is designed to support weight in one direction only  which is in a 
line through the bearings perpendicular to the races.

When you look at the bearings from side to side nearly half of each ball is 
supported by each race. In the vertical direction only about an 1/8th of the 
ball is supported and the force is such as to push the ball into the space 
between the two races while a side to side force pushes the bearings into 
the races.  Given the area and angles any weight is supported by a very 
small area on each ball. Any side force will cause the weight be shifted 
from all of the bearings down to only a few which could be as few as one to 

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


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