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Re: [TowerTalk] Thrust bearing / rotor load

To: David Gilbert <>
Subject: Re: [TowerTalk] Thrust bearing / rotor load
From: "Roger (K8RI)" <>
Date: Sun, 14 Jun 2009 00:24:29 -0400
List-post: <">>

David Gilbert wrote:
> WA3GIN wrote:
>> "I wonder how the ball bearings know the difference between vertical and 
>> horizontal loads and all the points between?"
> By the configuration and location of the races ...
As well as the bearing design, orientation, and materials.  Look at the 
orientation of the races and the split in the Ham series rotator.    Top 
and bottom races are horizontal with the split being perpendicular to 
the axis of the shaft. IOW they are for support only and not side 
thrust.  For one that does both, look at a wheel bearing. It uses 
tapered rollers aligned on an angle. Although the TB-3 has upper and 
lower races the split is about 45 degrees low on the outside so side 
thrust does not force the rollers into the split. Side force pushes the 
ball up and away from the split.  They will  support a load on the 
vertical axis but the materials (steel balls on an aluminum race) are 
not designed to support much of a load or a good combination to do so.   
Put a heavy load on them and the balls will "roll" flakes of Aluminum 
off the races.  There's a name for the phenomena but I don't remember 
it.    The best I've been able to get is about 2 to 3 years out of a 
TB-3 before the top race is riding right down on the base casting.  I 
hasten to add, changing out a TB-3 at a 100 feet with over 800# of 
antennas and mast is quite an experience (Read lots of work).  That is 
why I'm replacing the TB3s with DOM sleeves.  I think I may try double 
oil quenching those sleeves to get a hard surface that will wear 
better.  What I should do is fit them with Delrin sleeves for bearings.

Oil quenching does two things.  The rapid cooling of the surface makes 
it hard, while some of the carbon in the oil goes into the steel making 
"the surface" high carbon steel.  Water quenching makes the entire piece 
hard and thus brittle.

How well does this work?  A few years back I was shooting at some 
silhouette targets with a 9mm.  I should have inspected the targets 
before starting but didn't.  Some one had used a high powered rifle on 
the one target and left quite a crater.  One 9mm shot went in the crater 
on one edge and right back out the other which resulted in it coming 
right straight back and got me in the right leg with a lot of force just 
scraping the outside of the shin bone. One inch to the left and it would 
have busted my leg.  Fortunately I was standing at a slight angle and 
only lost some hide although it felt like I'd been hit with a baseball 
bat.  Also fortunate was we were shooting at what would be a fairly long 
range for pistols rather than at the typical 25 feet.

I took the targets home and used them as patterns to make new ones out 
of 1" thick steel plate which I oil quenched after fabrication.  Those 
high power rifle bullets only left skid marks on them after that. They 
would shatter water quenched targets. BTW these were animated targets 
that would move when hit, *sorta* like the ones you see at shooting 
galleries, but designed to handle a lot more power. (and a lot heavier)


Roger (K8RI)
>> "Always fun to read the various post on this reflector."
> That's for sure ...
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