[TowerTalk] thrust Bearing
grants2 at pacbell.net
Sat Dec 26 14:50:38 EST 2020
HOORAY Wilson!++ "Thrust bearing", the most misused word in hamradio
after "balun". Radial, thrust, and angular are the correct bearing terms.
In a related post, a TB3 is noted as a radial bearing. I admit its been
a long while since I tossed a trashed TB3, but remember it as an angular
design. Maybe, maybe not.
Here is the DXeng "advanced thrust bearing" cross section. Click to last
cross section picture.
It clearly shows it is an angular design, thus capable of radial and
thrust loads, IF it has some loading pushing the races together. The
contact angle of the balls to race seems about 45 deg, a design choice
which makes the thrust and radial load capacities about equal. Also
note the snap ring to prevent it coming apart, maybe even preventing
overturning of an unconstrained mast. Then a good WX seal.
IMO, if you must have such a bearing for some reason the DXeng is the
best design of the lot. For my towers, even with a 500# thrust load, a
radial bearing is what I use, only at the tower top.
Most deep groove ball bearing specs state maximum thrust and radial
loads, the thrust a small fraction of the radial.
HNY & 73,
On 12/26/2020 10:34, Wilson Lamb wrote:
> Why can't we get the terminology right?
> THRUST BEARINGS take THRUST loads, along the axis of a shaft, like a ships propeller shaft.
> I don't know if there's a specific name for radial support bearings, but they are the one's we have all around us, like in your car engine or BBQ spit.
> Yes, a thrust bearing will take up some radial load, but it usually isn't meant to.
> There are combination bearings, like the tapered roller bearings in your car wheel.
> A radial support bearing, if not built as a combination, won't be happy with much thrust load on it.
> Think of a ball bearing on its side. Thrust is driving the balls between the races, like a wedge, which will eat the races out on one side and eventually drive the balls out the side, if the outer race doesn't snap first.
> The Rohn sleeve won't take any axial load at all.
> To have a thrust bearing at the top of your tower you must have robust setscrews driven into the side of the mast very firmly, ideally in dimples.
> The screws may be in the top of the bearing assembly or in a collar around the mast.
> The screws must transfer the whole thrust load to the bearing's top race, then the balls/rollers transfer the load to the bottom race which transfers it to the tower.
> Yes, many thrust bearings use balls, but the races are horizontal. Two plates with marbles between would be way to think of them.
> I KNOW this is all old hat and obvious, but I've been pained by the misnaming on here for at least 15 years.
> Now it's off my chest...HAPPY NEW YEAR,
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