[TowerTalk] Thrust Bearing

[Roger (K8RI) on TT]

I ran the TB-3 and 4 dry and used the rotator a lot.  The bearings did 
not dimple much, but the races just wore out from repeated, cyclic 
lateral loads. The inside edge of the bottom race was like a razor.  
When the wind was over 15 mph those top antennas really moved.  At 20 to 
30 and above, I was amazed that the VHF and UHF antennas held together.  
At 30' above the bearing, I'm sure the load exceeded the bearing's load 
limits.  None of the antennas, by themselves presented much of a load, 
but 2 12L 2-meter C3i and 2 11L 440 C3i antennas on a 14' cross boom, 
about 30' above the bearing, a single 7L 6-meter C3i about 15' above the 
bearing, and a TH5 2' above the bearing added up to a major, lateral load,

I don't remember the figures, but the 144 and 440 antennas multiplied by 
30 and the 7L 6-meter antenna * 15 is a big number.

73

Roger (K8RI)


On 6/9/2015 10:50 PM, Gary - AB9M wrote:
> The reality is that a "thrust bearing" like the ones sold by Rohn 
> really don't need lubrication for one RPM and typical downward antenna 
> loads.  As long as there is a downward load on a "dry" TB3 or TB4 and 
> it is rotated periodically, the balls will stay round enough and the 
> upper and lower races will stay clean enough to provide years of 
> service. Its when you add grease, dirt, and water, then park the rotor 
> / beam at one heading for months that you shorten the life or destroy 
> a Rohn type thrust bearing.
>
> You can use more expensive greased trust bearings designed for other 
> applications, but they typically need additional protection from the 
> elements in order to prevent premature failures. If you are providing 
> radial force bearing protection, that can be accomplished with a hard 
> wood split board.
>
> 73 & DX,
>
> Gary - AB9M
>
> -----Original Message----- From: Wilson
> Sent: Monday, June 08, 2015 1:43 PM
> To: towertalk
> Subject: [TowerTalk] Thrust Bearing
>
> There are lots of kinds of thrust bearings, including the ones on the 
> front wheels of cars, which are for a combination thrust/radial loads.
> The pillow blocks with ball bearings are for minimal thrust loads and 
> will wear rapidly.
>
> http://www.bearingson.com/Category/4-bolt_flanges/cast_iron_4-bolt_flanges/ucf_series/default.asp?page=2&SortType=0 
>
>
>
> Here are some true thrust bearings:
> http://www.timken.com/en-Us/products/bearings/productlist/roller/thrust/Cylindrical/Pages/TP.aspx# 
>
>
> You can quickly recognize a ball thrust bearing, at least many of 
> them, because their outer circumference is split, so you see the balls 
> when you look in radially.
> Think of two big washers, with balls between, like the ball race in 
> your rotator.
>
> http://en.wikipedia.org/wiki/Thrust_bearing
>
> I think the term “thrust bearing” is widely misused.  Thrust is 
> parallel to the axis of the mast.  A thrust bearing carries the weight 
> of the mast and antenna.
> Many top bearings are just for radial force, the side loads caused by 
> wind, unbalance.
>
> WL
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-- 

73

Roger (K8RI)


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