The 3 large bolts with locking nuts used on tb-3's and tb-4's are more than
adequate to handle the weight of amateur installations and have never
slipped on me.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of JC Smith
> Sent: Friday, June 10, 2005 23:06
> To: 'Jim Lux'; 'Michael Keane K1MK'; towertalk@contesting.com
> Subject: Re: [TowerTalk] installingmonstermasts intowers(and
> ?twothrustbearings?)
>
> I'm sure you're right, Jim. There must be devices designed for this.
> They
> just don't seem to be supplied with any of the bearings typically supplied
> to us hams for this purpose. For me, I don't really need it anyway. The
> tower I'm installing will have an OR2800 rotor and I'm with Steve, I'm
> just
> going to let the rotor support the weight.
>
> 73 - JC, k0hps@amsat.org
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of Jim Lux
> Sent: Friday, June 10, 2005 12:00 PM
> To: JC Smith; 'Michael Keane K1MK'; towertalk@contesting.com
> Subject: Re: [TowerTalk] installing monstermasts intowers(and
> ?twothrustbearings?)
>
> At 10:53 AM 6/10/2005, JC Smith wrote:
> >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.
>
> There's a variety of wedgelock type clamps for shafts that can take a
> substantial axial load for a long time. The key is that they have the
> force
> distributed around the entire shaft, and they're designed so that the load
> tends to tighten the clamp.
>
> One can also put a ring around the shaft with an interference fit (i.e.
> heat the ring, cool the shaft).
>
> This is an application where there's a fair amount of flexing and
> vibration
> going on, which tends to make the shaft (which is a hollow pipe, after
> all)
> change it's shape and size. You're going to want something that prevents
> "creeping", which, to me, implies using some sort of fairly rugged
> permanent attachment (epoxy? welding?)
>
> _______________________________________________
>
> 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.
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