[TowerTalk] [Bulk] Thrust Bearings

[Grant Saviers]

YES!

Angular contact bearing is a common name for a bearing that can handle 
thrust and radial loads.  The races for angular contact ball bearings 
are tilted 25 to 45 degrees depending on the desired radial vs thrust 
load capacities.

They are prolifically used in machine tool spindles where both radial 
and thrust loads are inflicted on a cutting tool or lathe spindle.  In a 
milling machine ABEC 7 super precision radial ball bearings are common.  
A matched pair set (of not Chinese) bearings for a Bridgeport runs about 
$500.  Usually they are setup in matched pairs (id/od concentricity in 
micro-inches) back to back so thrust loads in both directions along the 
axis are resisted.  Tool grinders might use several pairs in tandem for 
super low runout.

Angled roller bearings are another approach as in your car wheel bearings.

Oversized ball bearings such as in pillow block assemblies can work as a 
combo thrust/radial bearing on a tower top plate.  Some are angular 
contact but not the usual case.  They work because a plain "deep groove 
ball bearing" can handle about 15% of its radial static load rating as a 
thrust load.  So a 2" id deep groove medium size ball bearing with a 
5,000# static radial load rating is good for 750# of thrust.

What is important for any metal on metal bearing is to keep the water 
out and to use a grease made for static loading.  When the grease film 
breaks down from a static load, fretting corrosion eats up the balls and 
race.  Keeping water out is hard and the appropriate greases are 
expensive and need periodic replenishment. Another life extending action 
is to periodically rotate any metal on metal bearing enough to cause the 
balls to rotate more than 360 deg, to replenish the oil film between the 
ball and race.  Leaving a rotator sitting for weeks at one setting 
invites degradation of the balls and races, "thrust" bearing and rotator 
bearings.

Polymer bearings are much better choices at the zilch rpm speeds of 
rotators and usual tower to mast tolerances.  Especially when I look at 
what is commonly sold as a tower "thrust bearing".  Been there, done 
that, never again.

Grant KZ1W

On 11/1/2015 8:39 AM, Wilson wrote:
> Can we get this terminology right?
> Thrust bearings take AXIAL loads off members, like the prop shaft on a ship.
> They don’t take lateral loads as a main function.
> Yes, there are some ball and roller bearings with tilted races that can take some lateral load.
> I don’t know if they have a special name?
> https://en.wikipedia.org/wiki/Thrust_bearing
> Even your auto’s crankshaft has a thrust bearing!
> WL
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