[TowerTalk] My first tower, Rohn 25G

Fri, 16 Jul 1999 13:48:45 GMT

Hello Roy,

You'll be pleased to know that there is a Rohn Dealer in Greensboro, NC. You 
can pick up your tower yourself and save some freight. I live in Southeast 
Virginia and a friend and I made a tower run to West Antenna last winter. 
Contact Harwood West (800) 632-0389 His email escapes me right now...
He also carries 2" OD, .25" wall 6061-T6 aluminum mast.

<<I've studied the Rohn catelog intently for the past 2 months.>>

That's a great place to start. Also check out the Towertalk FAQ pages:
http://www.contesting.com/towertalkfaq.html

<<The mast will be 4 ft. of 1.9" O.D. schedule 40 aluminum with a wall 
thickness of .145" >>

Roy, watch out here. "Schedule" is usually used to refer to water pipe with 
inferior grades of metal. Structural tubing, the good stuff, will have an OD 
on or near a size such as a multiple of 1/8 or 1/4". See if there are any 
mill markings on it to identify the grade of aluminum. if you see "6061", 
you should be ok.

If you don't know what the properties of this metal are, you will be taking 
a chance. (many old threads here) I'd buy some mast new, with known 
properties. You could even go taller. Try the MARC calculation software 
available from Champion Radio ( http://www.championradio.com/ ) to give 
yourself some real numbers and a feel for what is safe at the windspeed you 
want to be protected for.

<<  I'm going to use my new IIX ginpole kit with an 11 ft. section of the 
same stuff i'll use for the mast.>>

Hey Roy, I have the same ginpole kit. Again, the same warning here: If it's 
not 6061 or stronger aluminum, watch out! I selected 12' of 2"/.125" wall 
6061-T6 for my ginpole kit.
Also, the kit had a number of rough edges. Pay particular attention to the 
edges where the rope passes up through the head and round these generously 
with a file. The same applies to the outside flanges where the rope tends to 
rub when you twist the tower section around up top. Be sure to apply cold 
galvanize afterward! Also, don't forget the bottom of your ginpole mast 
where the rope enters.
I had trouble with excess friction due to the flat sheave design of the IIX 
kit, which allowed the rope to rub excessively on the pulley frame (rubbed 
right to shiny steel).  I replaced the flat sheave with
a deep, round-groove sheave from another pulley and was amazed at the 
friction reduction. This will give you and your crew much greater control 
over your sections. Amazingly, I found a pulley at an Ace hardware store, 
having a 650 lb rating, that has an ideally sized sheave (slighly larger 
rope diameter) retained by a locking pin. I had to buy a slightly larger 
bolt and drill out the ginpole head a little to retain the new sheave.

<< Not going to use preforms as i have no experience there and trust the 
regular method with 3 clamps and wrapping the dead end afterwards, even if 
it is more work.>>

This will work but please definitely reconsider this and use the far 
superior grips. I had a friend who felt the same way and went with clamps. 
Then, when he was helping out with my tower he discovered just how easy they 
are to work with and realized how much better they are. Now, his clamp bolts 
are showing some rust. Clamps will also creep over time and must be 
periodically retensioned to maintain their grip. If you have a friend who 
works for a local utility, you may be able to get cable and grips for cost.
Another neat thing about grips becomes evident whan you are raising the 
guys: you can pre-wrap one side of the grip on the ground, leaving the other 
side free like a hook. Then, you can pull the guy up to you with a rope and 
slip the free end right through your waiting thimble, taking the weight of 
the guy off of you right away. No fumbling with cable bending or hardware up 
the tower.

<< my measurements between the base and each guypoint was within 6 inches 
and same for guypoint to guypoint. Is this within an acceptable range?>>

This is plenty good!

Another very inexpensive and quick idea that keeps your tower extra strong 
in the wind is to step up one size larger in guy cable than what Rohn 
recommends. In your case, you would go from 3/16" to 1/4".
  This will be especially helpful if and when you decide to go higher in the 
future. I also live near the coast here in Gloucester VA, and am concerned 
about a direct hurricane hit and falling branches hitting the guys, even 
though the windspeed rating is 85 mph in my county. This upgrade gives you a 
tremendous improvement in strength and elastic control at very little cost.

Hope this helps and good luck with your tower project!

--...MARK_N1LO...--

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