I have a graveyard of 7-8 prop pitch rotators, all awaiting rebuilds one day.
In each case, failure resulted from water ingress, not mechanical stress. As
an experiment, a new method was tried: a silicone rubber sheet, folded into a
cone to form a shroud, was formed around the rotator. The top of the cone is
sealed around a 3-inch dia. Chromoly mast with stainless Aeroseal hose clamps.
At least now, the rotator is shielded against rain and heating from direct
sunlight exposure. The silicone sheet was ordered from Master-Carr. It's the
same torch-proof material that's used for tube exhaust chimneys in many desktop
RF amplifiers.
Regarding the weight distribution dilemma between a prop pitch rotator and
thrust bearing, I've never found a satisfactory answer based on facts. The
prop pitch supports a full-size 4 el 40m OWA at 140 ft and a 9 el 6m Yagi at
155 ft, both of which have 50 ft. booms.
A DXE TB400 thrust bearing recently replaced a similar Rohn type. The Rohn
bearing disintegrated into several pieces after just a few years. I've no idea
as to Rohn's thrust bearing composition, but it feels like "pot metal."
Paul, W9AC
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Paul F. Merrill
Sent: Sunday, June 22, 2025 3:35 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Thrust Bearing Concerns
Kurt told me that the PP is fine taking the weight and discouraged me from
having the thrust bearing take it all.
Paul / W7IV
On Sun, Jun 22, 2025 at 08:03 <towertalk-request@contesting.com> wrote:
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 22 Jun 2025 06:00:30 -0600
> From: Tom Hellem <tom.hellem@gmail.com>
> To: towertalk <towertalk@contesting.com>
> Subject: [TowerTalk] Thrust Bearing Concerns
> Message-ID:
> <
> CANyX0AqQ2w2hqpUzeLx_kTvfwPrZ5FVtbEYrtCiLj0dpwSk3uw@mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Looking for some input on the DX Engineering TB-400 thrust bearing.
>
> Here is the scenario:
> Rohn 55 tower supporting a large 6 meter EME array, in an "H"
> configuration.
> 4 yagis , each with 50' boom, and the main boom is also 50 '.
> The total weight is approx. 700 lbs.
> The rotor is one of Kurt's prop pitches, the small version (9,000:1).
> I believe the max thrust that can be handled by this rotor is 500 lbs.
> or so.
>
> We have purchased the DXE-TB400 thrust bearing to be installed on the
> BPL55G flat top. The hope is that this bearing can be used to support
> the entire weight of the array, thereby eliminating any thrust load on
> the rotor.
>
> Problem is, the documentation that comes with the bearing does not
> specify a max thrust load for it, nor does it give a torque
> specification for the three set screws that tighten against the mast.
> Furthermore, the upper half of the bearing is cast aluminum,
> so the threads for the 3 3/8" stainless set screws are aluminum. My gut
> feeling is that
> the aluminum threads are going to strip out before we can get enough
> torque on them to prevent the mast from slipping down and putting the
> entire weight of the array onto the prop pitch rotor.
>
> I am in no way suggesting that the bearing is not a good quality part.
> But I am concerned that we are asking too much of it.
> Another concern is that the bearing doesn't come with a grease fitting.
> This setup is located near the coast of Oregon, they get a lot of rain
> there.
>
> Anybody have suggestions how we can improve this setup?
>
> All input is appreciated.
>
> Tom Hellem
> K0SN
>
>
> ******************************************
>
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