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Re: [TowerTalk] installingmonstermasts intowers(and ?twothrustbearings?)

To: "'JC Smith'" <jc-smith@comcast.net>,"'Michael Keane K1MK'" <k1mk@alum.mit.edu>,<towertalk@contesting.com>
Subject: Re: [TowerTalk] installingmonstermasts intowers(and ?twothrustbearings?)
From: "Dick Green WC1M" <wc1m@msn.com>
Reply-to: wc1m@msn.com
Date: Sat, 11 Jun 2005 03:26:40 -0400
List-post: <mailto:towertalk@contesting.com>
My MA770-MDP has only a single set screw to hold the mast. For this reason,
I always rest the boom-to-mast clamp on the rim of the top section. That
way, the mast can't slip into the tube. In addition, I think it's a very
good idea to keep the antenna low on the mast to minimize the moment arm at
the top of the tower. I believe these tubular jobs are rated with the load
no more than a foot or so above the top section.

73, Dick WC1M 

> -----Original Message-----
> From: JC Smith [mailto:jc-smith@comcast.net] 
> Sent: Friday, June 10, 2005 1:54 PM
> 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
> 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.

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