I have had the same experience with my tower. The Rohn AS455G Rotor Plate
is quite strong and should be able to support much more weight than the
typical rotor, mast and antenna(s). In addition, the Rohn TB3 Thrust
Bearing is very robust and will likely handle far in excess of the vertical
and lateral forces one would see with Ham antenna installations.
73, Keith NM5G
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Roger K8RI on Tower
Sent: Wednesday, June 08, 2005 11:34 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] installing monster mastsintowers(and ?
twothrustbearings?)
> OK, I asked the original question, but as the thread has wandered a
> bit, let me throw in .02 here. The thrust bearing I have on my
> TX-472MDP is plenty HD enough to support just about any mast, but the
> "locking collar" that sits on top of the bearing only has one small
> set screw to clamp it to the mast.
All of the Thrust bearings I've had here had three, 3/8" bolts, or 5/16ths
bolts to center and hold the mast. They are designed to hold weight in both
the vertical and horizontal directions.
> It definitely is not designed to support ANY vertical load. I believe
> the THRUST in these radio tower thrust bearings means the lateral
> force applied by wind, etc, and not the downward force of gravity.
> That's not to say that some bearings don't support load, but the one
> that came with this TX-472 sure isn't designed to do it. I suspect
> most others we see on towers are the same way. Check your rotor
> specs... I suspect any rotor sized to turn a particular array will
> also support its weight. Mine supports 1800#.
> That's
> four or five times the load that will be on it.
Some rotors need the weight, or part of it.
It is very difficult to evenly distribute weight between supports such as a
rotator and thrust bearings. Thermal expansion and contraction can change
the distribution dramatically.
As was said earlier, we need to know the specifics for each piece of
equipment in our instalations.
Some thrust bearings are meant to absorge lateral thrust, but not linear.
Others are so designed.
In my array the top antennas are 30 feet above the top thrust bearing. In
high winds this would put tremendous lateral thrust at the rotator which is
why I have a thrust bearing above the rotator. The rotator is quite
capable of supporting the entire load and generally does. However during
work, or removing the rotator all I have to do is release the mast clamp
which lets the mast down. It's hardly enough to see the mast move, but all
of the weight transfers to the thrust bearings which allows for easy removal
of the rotator.
Roger Halstead (K8RI and ARRL 40 year Life Member) N833R - World's oldest
Debonair CD-2 www.rogerhalstead.com
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of Alan NV8A (ex.
> AB2OS)
> Sent: Wednesday, June 08, 2005 7:43 AM
> To: towertalk@contesting.com
> Cc: David Robbins K1TTT
> Subject: Re: [TowerTalk] installing monster masts in towers(and ?
> twothrustbearings?)
>
> On 06/08/05 10:04 am Alan NV8A (ex. AB2OS) tossed the following
> ingredients into the ever-growing pot of cybersoup:
>
>> On 06/08/05 07:37 am David Robbins K1TTT tossed the following
>> ingredients into the ever-growing pot of cybersoup:
>>
>>
>>>> *Don't rely on the bearing's set screw to support any of the
>>>>dead weight of the mast/antenna/coax.
>>
>>
>>>Ummmm, it wouldn't be much of a 'thrust' bearing if the set screws
> couldn't
>>>hold the weight of the mast.
>>
>>
>> The thrust bearings I have seen are almost capable of supporting a
>> heavy
>
> Oops! I meant " . . . almost *certainly* capable . . ."
>
> Alan
>
>
>> load, but they had no integral means of clamping the mast: there was
>> a separate "collar" secured to the mast by set screws, and this
>> collar then rested against the center part of the bearing.
>>
>> In normal operation, wouldn't the rotator itself support most of the
>> downward force?
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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