[TowerTalk] [Bulk] Thrust Bearings

[Big Don]

The W8JGU Sidemount is reviewed by Randy K5ZD in a late 1980's issue of
NCJ. Very simple. It uses *No* precision ball or roller bearings. The
radial loads are taken by a rotating pipe inside a slightly larger pipe (2
places). Axial (downward) loads consisting of the antenna weight plus the
swing-arm & pipe "mast' weight are taken by a CIRCULAR FLAT STEEL PLATE
SUPPORTED BY A STEEL FLAT PLATE RING on the bracket to the tower. The two
flat plates rub together forming the axial bearing. We have used one
successfully with a 402CD beam up for 25 years. Ours has grease fittings at
key locations. The "bearings" work fine. We did make some rotor-mount mods
to make it "full floating" for better alignment. The difference in rotating
friction compared to precision bearings is negligible. There is no wear at
the low rotor speeds.

When precision ball bearings or tapered roller bearings fail, there can be
damaged pieces that severely jam the rotation. Can't easily happen just
rubbing two flat plates together. This kind of support would likely work
even better in a conventional straight up rotor/mast/antenna setup,
compared to a sidemount installation, since there would not be the large
off-center loading.

Could not find an online link to the NCJ review but can email copy of the
undated page upon request.
This page has a good drawing of the unit and additional explanation.

Don  N7EF .


On Sun, Nov 1, 2015 at 10:05 AM, Grant Saviers <grants2 at pacbell.net> wrote:

> 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