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Re: [TowerTalk] TB-3 Thrust bearing

To: "Richards" <>
Subject: Re: [TowerTalk] TB-3 Thrust bearing
From: "Dubovsky, George" <>
Date: Mon, 3 Nov 2008 14:33:04 -0500
List-post: <">>
That particular thrust bearing implementation has been around for at
least 40 years; its performance and flaws are well documented. It's
highly unlikely that anyone still associated with its manufacture or
sale knows any of the original design decisions that might allow them to
offer more than the collected "common knowledge".

The bearing is steel balls in aluminum races. It is nominally
weather-sealed when mounted in its intended orientation. It is a good
performer when used regularly. If the antenna mast is left in one
position for an undefined "long time", and the wind causes the antenna
system to rotate the mast back and forth through whatever small angle
the free play in the rotator system allows, the steel balls *can* fret
the softer aluminum races, digging small pockets in the aluminum,
resulting in a characteristic gritty or lumpy feel on rotation. Because
of the open design of the bearing, it would seem prudent to not add
anything to the bearing system that would encourage airborne
contaminants (like dirt, grit, bird droppings) to stay inside the
bearing housing. The bearing is unsealed on the bottom also, so if dirt
enters the bearing, it will eventually fall back out - unless you have
added grease.

Once the bearing has been trashed, there is not a lot you can do to
repair it. As reported elsewhere, you can smooth out the worst of the
damage with something like a Dremel tool, and return the bearing to
service, but it will never be like a new one. You can lathe-turn the
races up to the next size standard ball, but it's difficult to re-work
the port where the balls must be introduced and you are left with
thinner aluminum behind the races. I have even modified one to use a
Nylatron (molybdenum-disulfide-loaded Nylon) slug as a replacement for
the entire ball-bearing system - that one should last "forever".

The Rohn design is a good solution for an extremely low-tech problem: 1
rpm, modest axial and thrust loading, mostly benign operating
environment, and (originally) ham-cheap.


geo - n4ua

-----Original Message-----
[] On Behalf Of Richards
Sent: Monday, November 03, 2008 1:50 PM
Subject: Re: [TowerTalk] Thrust bearing re-grease

I am repeatedly intrigued how many hams will disregard the
manufacturer's design and specifications, in favor or some
some well-intentioned, and often commonsensical, alternative
solution.  Or how they might ask their well intentioned buddies,
before they inquire of the manufacturer, what is the correct part or
method to employ.  In this way, they often re-engineer the product
and substitute different components and methods.

An example is where the operator wants to add guy wires to his
self-supporting tower.  At first blush, it would seem sensible enough,
like wearing a belt with your suspenders... but on further analysis,
it is dangerous because it adds unwanted, and apparently unexpected,
downward forces that can overs-stress the support cable and cause it
or other components to fail.

In the instant case, the operator plans to grease a grease-free
component.  While it seems a commons sense plan to grease
the gnashing metal gears,  it proves counterproductive and
possibly harmful to do so.

But my instant curiosity is why the operator did not ask the
manufacturer about the plan, first.  After all, the manufacturer
is, presumably, the best informed party concerning its product.
And, if not, then maybe you want to get goods made by some other

Just MY take, anyway....  of course your mileage may vary.

==================  K8JHR  ================== wrote:
>     In all things, follow the LXC Prime Directive to  "DO what the 
> manufacturer says" and you'll typically have better and safer


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