Well said. I agree.
<bogart mode>
You race? What car, motor, type of racing?
</bogart mode>
Keith
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Tom Rauch
Sent: Thursday, July 15, 2004 5:03 AM
To: Jim Lux; Michael Tope; K8fu@aol.com; towertalk@contesting.com
Subject: Re: [TowerTalk] Erections (TWR)
> 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
_______________________________________________
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_______________________________________________
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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