At 12:33 PM 6/8/05, Roger K8RI on Tower wrote:
>All of the Thrust bearings I've had here had three, 3/8" bolts, or 5/16ths
>bolts to center and hold the mast. They are designed to hold weight in both
>the vertical and horizontal directions.
Well, some of the generalizations about about what's typical have left me
confused. I do recognize the above description as something more familiar,
the Thrust Bearings that Rohn sells, the TB3 & TB4. For me, those are the
sorts of bearings that first come to mind when we start talking about
thrust bearings.
All that's been said has left me confused enough to ask: does anyone know
definitively whether a Rohn TB3 is designed as a radial bearing for taking
lateral loads or a thrust bearing for taking axial loads?
What I recall from having disassembled several TB3's for refurbishing many
moons ago, is that the balls are contacted between races in the top and
bottom faces of the bearing and not between the inner and outer walls.
To me, that makes a TB3 a thrust ball bearing by design and implies that a
TB3's intended primary function is to carry axial loads. It's comes as
something a bonus that a TB3 also transfers radial (wind) loads to a
degree; a TB3's ability to perform that task would be limited by the
bearing's radial load limit.
If one's primary concern was transferring wind loads rather than carrying
weight, then a radial bearing is what should be used and not a thrust
bearing. In that case the bearing functions as a very well-lubricated bushing.
It would seem that all my tower experiences have been with bearings that
were designed to function as thrust bearings. I can't remember ever
encountering a radial bearing being used at the top of the towers I've
worked on.
73,
Mike K1MK
Michael Keane K1MK
k1mk@alum.mit.edu
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