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[Towertalk] Rohn 25G Questions

To: <>
Subject: [Towertalk] Rohn 25G Questions
From: (Stan & Patricia Griffiths)
Date: Thu, 8 Aug 2002 15:57:20 -0700
Hi Guys,

I inserted a few comments in the message below:

----- Original Message -----
From: <>
To: <>; <>
Sent: Tuesday, August 06, 2002 7:12 PM
Subject: Re: [Towertalk] Rohn 25G Questions

> In a message dated 8/6/02 6:53:43 PM Pacific Daylight Time,
> writes:
> > Why are the holes on the section legs 2 different sizes? One is 3/16'
> the
> > other is 1/4". Can I drill out the 3/16" holes and make them 1/4" like
> > rest or should I leave well enough alone?
> >  I called an engineer at Rohn yesterday and he told me that he had no
> > why they did it that way. He said they were engineered in the 60's.
>     Well, that's your answer. If Rohn doesn't know - no one on TT has any
> better answer.

I asked this same question of Rohn some time ago and got a similar answer
from them.
Essentially they said 25G was designed so long ago that nobody around there
remembers why they use two sizes of bolts.  They do this on 45G, too, but
only one size on 55G.  I tried to apply some common sense to this (sometimes
gets me into real trouble . . . ) and I thought about exactly what those
bolts are doing.
Obviously, they are in shear as the weight of the tower and antennas plus
the downward
pull of the guys is on them.  They need to be at LEAST big enough in
diameter to resist
the total load in shear.  My guess is that two bolts of the larger size
would be over-kill
for shear in this application and two of the smaller size would not be
enough in shear.
The reason you would not go for two of the large size is that you don't want
to drill
out any more leg material than necessary since that would weaken the leg
when there is sideways force on the tower tending to buckle the sections.
If you have
seen a section that has folded over at a joint, you will have noticed that
the bolts tend
to "pull through" the end of the leg material.  This is exactly the failure
mode I observed
on a Rohn 25G Foldover that was too heavily loaded at the top and it
while being cranked up.  Maybe I am all wet on this, but it makes some sense
to me . . .

> >  Last but not least, where can I buy Rohn accessories for a 25G? Guy
> > brackets, etc.
>     Texas Towers and National Tower are long time Rohn dealers with
> competitive prices. Also W7NI at Antronics is a good source.

I appreciate the publicity, Steve, but I have sold my tower business to K7PN
I only have a small stock of some of the ubolts I had specially made left.


> Cheers,
> Steve    K7LXC

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