[TowerTalk] thrust bearings

[Grant Saviers]

What IS required is a radial bearing for flat plate top towers. A thrust 
bearing is only needed if the dead load exceeds the rotator capacity, 
which takes quite an antenna stack.  The bearings in rotators are 
generally of an angular contact design. Angular contact bearings are 
used when a combination of positive or negative thrust and radial loads 
are applied such as in milling machine tool spindles.  In those 
applications they are made to super tight tolerances and provided in 
back to back matched pairs so that clamping them tightly together 
provides the needed preload so the spindle doesn't move radially or 
axially.  So to enable rotators with single angular contact bearings to 
handle the thrust and moment/radial loads they need preload.  The HD 
rotators with two opposing races are better able to handle the loads 
both ways, although I think the tolerances are pretty large and preloads 
are low/none.  They are much better at resisting an applied moment such 
as a rotator with an unsupported mast above.

UST crankups (like my HDX589s) have a 5" long pipe sleeve, hot dip 
galvanized, which a 2" mast slips into, so there is no thrust capacity.  
Zn on Zn galvanizing is the "bearing" but lasts.  My Orion 2800 is rated 
1800# thrust load and the Yaesu 2800 in the other is rated 661#, so not 
a problem for my mast plus antenna loads.  btw the Orion has separate 
radial and thrust ball bearings to get the capacity.

For towers with a flat top plate, my choice is to use a UV resistant 
UHMW block bored to just oversize the mast diameter and 2 to 4" thick 
depending on the antennas above. Bolt pattern per the tower top plate.  
No maintenance, no ball/race fretting (the pits you saw), no water 
ingress worries, and lasts a long time. Other plastics work and some 
have posted that they use a rot resistant hardwood block such as white 
oak or teak.

I haven't held a DXE bearing but the design is better than Rohn or Yaesu 
and given my experience with other DXE fabricated parts I suspect the 
materials are superior as well.  Their Summit Racing heritage shows.  My 
prior experience with Yaesu and Rohn "thrust" bearings matches yours or 
worse.

Grant KZ1W

On 10/6/2018 8:57 AM, knowkode at verizon.net wrote:

> Greetings All,
> I have used Rohn TB3 thrust bearings in the past without issue but I have seen my fair share of worn out  bearings due mainly to an antenna being parked in one direction for a long time- pitted races were the result. I've no experience with anything else and that brings me to my question. Is there something better out there? DXE claims an improvement over the Rohn bearing but it looks as all they did was add a lower seal. I'm leery of Yaesu if the bearings are made from the same pot metal as their rotor mast clamps. Bearing recommendations for an installation with a 2" mast  with about 8' above the bearing and 2' below and an antenna along the lines of JK's C3S antenna are sought.
> Tnx es 73,JimW5QM
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