[TowerTalk] Thrust Bearing Installation

[Grant Saviers]

If yours are commercial ham "thrust bearings" they aren't.  Rather an 
angular contact bearing which can handle some combination of thrust and 
radial loads depending on the design.

It takes a mighty large antenna array to exceed the thrust (dead weight 
of mast + antennas) load rating of ham rotators.  Most have specs. Most 
are angular contact ball bearing designs which need a thrust load to 
stay centered and handle radial loads.

What is needed at a tower top is a means to manage the side and torque 
loads created when wind creates those loads on the mast and antennas.  A 
tube sleeve is used on UST crank ups.  For a flat top tower, my 
preference is a UHMW plate (UV resistant) bored to the mast diameter. 
Never rusts and lubrication isn't needed. Cheap.  Radial only.  Some use 
stacked cutting boards, even impregnated hard woods.

Three bearings (including angular contact) on a shaft are a bad idea, ie 
"two thrust" + rotator.  Never done in machinery, pumps, etc since one 
of the bearings will be overloaded (except for super precision "duplex 
pairs" mounted back to back in machine spindles = $$$).  Might not 
matter given the slop in ham "thrust bearings."

Rotators and "thrust bearings" are often steel balls in aluminum races 
which have a great collection of things to go bad.  Cost is right though.

Grant KZ1W


On 12/21/2020 13:51, krgoodwin at comcast.net wrote:
> Installing a thrust bearing in a tower - Dead weight (along the gravity
> vector) all on the rotator or all on the thrust bearing?  Seeing such things
> as sleeves for towers, I would surmise that all of the dead weight is on the
> rotator and only off-axis loads (perpendicular to the gravity vector)  are
> handled by the thrust bearing.  I use two thrust bearings in my tower which
> I don't believe effects the answer to the above question.  Ken K5RG
> 
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