If one wants to relieve the vertical weight, back-to-back galvanized U-bolt
saddles fastened with a couple of grade 5 bolts is a much easier (and maybe
much safer) solution, and doesn't weaken the mast. All you need to do is
grind off their tips to allow for pulling them tight without hitting each
other. I used this setup on the upper thrust bearing. The lower bearing is
left "loose" and will only be used for mast stabilizing for future rotator
pulls. It worked like a charm with a pair of Rohn bearings. I wanted the
weight off the rotator so I could easily pull it when needed without having
to mess with the mast first.
73, Jerry W5KP
----- Original Message -----
From: "Chuck Lewis" <clewis@knology.net>
To: <W8JI@contesting.com>; <towertalk@contesting.com>
Sent: Monday, December 17, 2001 1:19 PM
Subject: Re: [TowerTalk] Hink and Kinks
>
> I had the same reaction when I read it, and also the same question
regarding
> editorial review of QST articles.
> Furthermore, the previous hint, from the same submitter, has us drilling a
> hole in the mast just above the thrust bearing in order to transfer
vertical
> loads to the bearing so we don't have to rely on the jam-nutted bolts
> normally used through the bearing upper collar. I can't think of a worse
> place to weaken a mast: right at the point of maximum bending stress.
Sure,
> we've argued over drilling and pinning masts to rotator upper brackets,
but
> that's in a relatively safe spot. I can see it now...hundreds of ten-foot
> lengths of two inch water pipe being drilled for a 3/8" bolt right at the
> prime failure point.
>
> This brings up a pet peeve: Why are we so determined to remove the
vertical
> load from rotors unless it exceeds the makers specs? I'm an EE, not a
stress
> guy, so my credentials are questionable, but my intuition tells me that
> rotors DEPEND on some vertical preload to obtain lateral (radial?) load
> reaction from their bearing races, and to maximize bearing life. Sure,
each
> rotor design will treat this a little differently, but their specs will
> account for it, and they all seem to be clear on the allowable vertical
load
> for the size of the rotor. My Rohn "thrust" bearing is set up with the
> jam-nutted screws just clear of the O.D. of the mast, so the "thrust"
> bearing is reacting against RADIAL thrust loads and reducing the
overturning
> load applied to the rotor (NOT the weight of the mast plus antenna). My
> total "stack" weight is well within the allowable vertical load as
specified
> by the rotor manufacturer; and is constant, so there was no good reason to
> reduce it. On the other hand, wind-induced overturning moments could
> conceivably exceed the capability of the rotor, and the "thrust" bearing
is
> there to add additional protection against excessive bending loads at the
> rotor. The bending load becomes zero-ed out by the "thrust" bearing, and
the
> rotor races are subjected to lateral (radial) forces instead. Having a
> vertical pre-load ensures that these races have a chance to do their job.
> When I check things at the top, I make sure the bearing collar will rotate
> around the mast and that the jam-nutted screws are still just clear of the
> mast OD. AND...there are never any alignment problems.
> Now...had I placed a BIG stack up there, with a vertical load which
exceeded
> the allowable for the chosen rotor, a thrust bearing that shared some of
the
> vertical load would have been appropriate. In that case, however. the
> hint/kink we're bashing becomes even scarier!
>
> Chuck, N4NM
>
> ----- Original Message -----
> From: "Tom Rauch" <w8ji@akorn.net>
> To: <towertalk@contesting.com>
> Sent: Monday, December 17, 2001 12:28 PM`
> Subject: [TowerTalk] Hink and Kinks
>
>
> >
> > Re: Add Safety and Comfort Jan QST page 67
> >
> > This seems like a death wish!
> >
> > I can't imagine standing on a rubber hose that was slit and installed
> > over a tower rung....even if it is RTVed in place!! All it needs to do
> > is spin, and woops...there go your feet out from under you
> >
> > Does this concept bother anyone else, or am I paranoid about
> > having a solid foothold?
> > 73, Tom W8JI
>
>
>
>
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>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
>
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
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