Does anyone know a source for 9mm (.125 pitch) bolts? Everyplace I check
seems to jump from 8mm to 10mm. I only need one, and the length isn't
critical (longer is better).
Thanks & 73 - JC, k0hps@amsat.org
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of JC Smith
Sent: Friday, June 10, 2005 10:54 AM
To: 'Michael Keane K1MK'; towertalk@contesting.com
Subject: Re: [TowerTalk] installing monstermasts intowers(and
?twothrustbearings?)
Mike,
There are obviously different bearing sold to amateurs for the top of their
towers. Although I have not disassembled it to look at the location of the
races, my TX-472MDP's TB-2US is obviously not designed to support any axial
weight. It's obvious because the only means of clamping the mast to the
bearing is a single, allen/socket-head set screw. No way is anyone ever
going to tighten that enough to support the axial load of even a moderately
sized mast and antenna. I also have a MA-550MDP with rotor base. Now
there's a thrust bearing that's designed to support some weight.
Incidentally, even though the top of this tubular tower does have fairly
heavy-duty mast clamping arrangement, my mast still slipped down inside the
tower until the antenna (a little 3L tribander) rested on the top of the
tower. Fortunately, no coax got pinched and since the whole tower rotates,
no real harm was done. The mast does weigh about 70# but still a relatively
light load considering the small antenna. The antenna was only 10' above
the tower top. What that taught me is that when you get that mast whipping
around a little (and we don't have much wind here) you really can't rely on
any of these collar clamps to support an axial load over a long period of
time. You'd have to run a hardened pin through the collar and mast to be
guaranteed no slippage over time, and I don't think that's recommended
either.
73 - JC, k0hps@amsat.org
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Michael Keane K1MK
Sent: Friday, June 10, 2005 9:16 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] installing monster masts intowers(and
?twothrustbearings?)
At 12:33 PM 6/8/05, Roger K8RI on Tower wrote:
>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.
Well, some of the generalizations about about what's typical have left me
confused. I do recognize the above description as something more familiar,
the Thrust Bearings that Rohn sells, the TB3 & TB4. For me, those are the
sorts of bearings that first come to mind when we start talking about
thrust bearings.
All that's been said has left me confused enough to ask: does anyone know
definitively whether a Rohn TB3 is designed as a radial bearing for taking
lateral loads or a thrust bearing for taking axial loads?
What I recall from having disassembled several TB3's for refurbishing many
moons ago, is that the balls are contacted between races in the top and
bottom faces of the bearing and not between the inner and outer walls.
To me, that makes a TB3 a thrust ball bearing by design and implies that a
TB3's intended primary function is to carry axial loads. It's comes as
something a bonus that a TB3 also transfers radial (wind) loads to a
degree; a TB3's ability to perform that task would be limited by the
bearing's radial load limit.
If one's primary concern was transferring wind loads rather than carrying
weight, then a radial bearing is what should be used and not a thrust
bearing. In that case the bearing functions as a very well-lubricated
bushing.
It would seem that all my tower experiences have been with bearings that
were designed to function as thrust bearings. I can't remember ever
encountering a radial bearing being used at the top of the towers I've
worked on.
73,
Mike K1MK
Michael Keane K1MK
k1mk@alum.mit.edu
_______________________________________________
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
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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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