[TowerTalk] [Bulk] Re: Thrust Bearing

[Grant Saviers]

I've not had good service from the TB series and now use a UHMW block 
bored to the mast diameter plus about 0.040" as a radial bearing or the 
block plus a collar with a stainless disk on the bottom as a combo 
radial and thrust bearing.  Black UHMW is reasonably UV resistant and is 
an excellent low speed bearing material.  Never rusts, never needs 
grease, or other maintenance and lasts a long time.  A 6x6x1.5" black 
UHMW block costs $21 from McMaster.

The pillow block/flange bearings that use radial ball bearings are 
another choice which do work, but should be protected from water and 
greased periodically.  They are primarily designed for radial loads but 
have a thrust capacity of about 15% of the maximum static radial load.  
For a 6211 ball bearing which is a size close to 2" bore the maximum 
static radial load is 6550#, so a 1000# thrust load won't overload the 
bearing.

However, the small oscillating loads from an antenna sitting unused and 
moving slightly in the wind will squeeze oil out of the ball/race 
contact area.  Then fretting corrosion will likely cause premature 
bearing failure even in a weather protected and regularly greased 
bearing.  The Ham-V and TT rotators I've taken apart all show ball 
dimples in the races from this.  Add some water and the process is 
greatly accelerated.

Grant KZ1W

On 6/9/2015 19:50 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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