[TowerTalk] Erections (TWR)

[GALE STEWARD]

I've had R25 installed at two different QTHs for
something like 34 years. I usually do a twice a year
inspection, top to bottom. I've never found a loose
bolt in all those years. These are Rohn bolts & nut
without any lockwashers or any kind of loctite. FYI...

73, Stew K3ND



--- Tom Rauch <w8ji at contesting.com> wrote:
> >  I don't know what the torque specs are for Rohn
> 25, but
> the
> > > steel tubing they use for the legs is soft
> enough that
> it will yied
> > > slightly when you tighten up the bolts. In that
> sense,
> the tower leg
> > > sort of becomes like a bellevue washer.
> >
> > And the bolt stretch, too...
> 
> Bolt stretch and thread distortion is what keeps the
> headbolts tight in your car engine (unless you own a
> Caddy
> with the very long bolts) and the lugnuts tight. As
> a matter
> of fact the critical bolts in my racing engine are
> tightened
> to a specific amount of stretch, rather than torque.
> 
> The bolts won't stretch or distort in a Rohn 25
> enough to
> lock threads, however. The metal in the legs is far
> too
> soft. You still don't need a lock washer. Nor do you
> need to
> excessively tighten the bolts, which mostly serve as
> pins.
> There really isn't anything making the nuts back
> off. They
> won't come loose unless the metal wears away from
> the joint
> rocking.
> 
> > Fine threads require huge torques to get high
> axial loads.
> 
> Coarse threads require huge torques to get high
> axial loads.
> Fine threads require less torque.
> 
> In almost any case, the cause of a bolt loosening is
> loss of
> material under the fastener heads, excessive torque,
> or
> under torque. A lock won't fix that. Once you
> overload the
> bolt or material under the bolt, you often have a
> bigger
> problem than having it a bit on the loose side.
> 
> A soft thin round material normally requires some
> type of
> load spreading washer like a thick hard flat washer
> commonly
> used on aluminum like cylinder heads. The washer
> would have
> to be a tensioning type, like a "split ring" lock,
> if you
> could not reach the point of thread distortion or
> bolt
> stretch.
> 
> All of that, however, is totally unnecessary in Rohn
> 25. The
> legs are weak and they are round, so the bolt and
> nut have
> huge pressures in a small area with only modest
> torque. Even
> fairly low torque flattens the leg in a small area
> and locks
> the joint. If you tighten so much you distort the
> leg
> outside of the bolt head and nut, you are grossly
> overdoing
> it.
> 
> If you needed locking hardware or chemicals, I'm
> sure Rohn
> would have supplied it with the bolt kits.
> 
> 73 Tom
> 
> 
> _______________________________________________
> 
> 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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