I thought Marty stated he's using HDPE, that's hi density poly
ethylene (not teflon) for the main insulator, and uses teflon (PTFE)
for the bolt sleeves and washers. Looks to me that the main
compression force (and weight of the tower), if I understand it
correctly, is on the 1" thick HDPE "plate" and less so on the washers
and sleeves. I suppose the teflon washers could squish when
tightened; but with only 1/2" of material it can't really go
anywhere, can it?
Chris
KF7P
On Dec 23, 2009, at 17:12 , Roger (K8RI) wrote:
I haven't read all of the replies yet, but Teflon is a poor structural
material. If under compression or expansion it will move. It "cold
flows" substantially, like an extremely thick taffy. I used it for the
base insulator on a mobile antenna. In less than 20 miles the antenna
was swinging around at almost a 45 degree angle. I had to stop and guy
it into the car through the windows using heavy fishing line.
Delrin, or the strongest ...fiberglass painted with a UV protecterant
should work fine.
73
Roger (K8RI)
brahmangou@aol.com wrote:
> 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
> insulating
> 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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>
>
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