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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