[TowerTalk] installing monster masts intowers(and ? twothrustbearings?)

Michael Keane K1MK k1mk at alum.mit.edu
Fri Jun 10 12:16:20 EDT 2005


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 at alum.mit.edu



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