The Teflon rod would spread the weight of the tower over 4 square inches or
so: marty's would spread it over 40 or so, about a 10 to 1 difference. I'd
think deformation of a sheet of Teflon would not have a safety issue,
wouldn't you? The tower is guyed.
He HAS, however, built a home-made capacitor to ground. Depending on the
value of that capacitor, screwey things might arise regarding RF current to
ground, but I 'spect it will work OK anyway.
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Subject: Re: [TowerTalk] Making an insulated base for 80 meter vertical from
One comment on Teflon.
It is SOFT and will deform rather easily under stress, whether expansion OR
compression. Do some testing before you put a lot of force on it.
My original idea was to use Teflon rod for my insulated tower bases, but
changed that IMMEDIATELY upon discovering the deformation that occurred just
with the weight of the base legs on the insulators in static position.
Now using (as previously done) fiberglass rod which can be purchased in 6'
lengths at a farm supply store, disguised as 'electric fence posts'. They
are exactly the right size for my purpose, being 1.25"
in diameter, and fit snugly within the tower leg supports.
> Hi Guys,
> I got a few emails asking where I got the insulated base. I made it.
> The insulated legs on the market are pretty expensive, and I didn't
> like that they are in tension and compression when the tower moves
> with the wind and under other external forces. It appeared to me, and
> I may be wrong, that the insulating material might not be as
> strong/durable as the original tower legs.
> I bought a 1" thick 24" square HDPE cutting board from a commercial
> restaurant supply , about 18 dollars, and drilled it to fit over the
> j-bolts in
> a standard Rohn 3'x3'x4' concrete tower base. I put the Rohn tilt
> base on top of the cutting board. There are several machine shops on
> ebay that sell PTFE teflon machining end pieces, leftovers. I bought
> a couple of short 1 1/2" teflon rod pieces, 6 dollars, and
> drilled/turned them to fit in the annular space between the bolt
> holes in the tilt base and the edges of the j-bolts as insulating
> bolt sleeves. Then I took a short piece of 3" teflon rod, 3 dollars,
> and sawed 1/2" thick disks off of it. I drilled through the disks and made
insulating washers for each of the base bolts.
> This way all of the plastic parts are always in compression, at their
> strongest. I used teflon for all of the parts that are exposed to the
> sun to avoid UV breakdown of the insulators, also teflon is a superior
> material for the thinner (3/16" thick) bolt sleeves. By using the
> tilt base, I
> can lower the tower to make adjustments and repairs in the future ( not
> getting any younger, hi hi). I'm ready to install install the
> tower sections
> and run the feed line as soon as the weather clears up.
> Marty Haley AB5GU@ARRL.NET
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