Agree. Rulon and TFE filled or plain polyamides (e.g. Vespel) are
indeed "crazy expensive" and not at all needed for radial or thrust.
UHMW is a small fraction of their costs and works just fine at the PV's
(pressure x velocity) that is found in tower/mast rotation systems.
UHMW will creep more but that makes little difference in a tower thrust
or radial bearing. My 3" x 22' mast thrust + radial bearing is a 5"
diameter 1/4" SS disk screwed with flat head screws to an aluminum
sleeve with 8 grub screws to secure it to the mast. The disk rests on a
6x6x4" UHMW block bored 3.040" for a 3" mast. I think the parts cost
was $50 for UHMW, plus $40 for the 6061 and SS and bolts (I did the
machining).
I designed a 10.5' tall swing arm assembly for mounting two large yagis
and it has a UHMW bearing as I described at the top but then decided to
use individual ring rotators.
Grant KZ1W
On 11/1/2015 12:06 PM, Charles Gallo wrote:
Actually, that will work, but you would probably be better off with a bronze
ring, or even better today, one of the many engineering grade plastics.
Unfortunately, some of the better are crazy expensive unless you either cast to
shape, OR use small diameter rod on end as inserts onto say your steel ring.
They use some of these plastics for things like the turntable bearings on
cranes, just in case your worried about low turning rate, high load, dirty
environments. Never have to lubricate them too
--
73 de KG2V
Charlie
On Nov 1, 2015, at 2:37 PM, Big Don <bigdon39@gmail.com> wrote:
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@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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|