I can certainly understand your feelings toward the stressing of fiberglass
rod based on the failures you have seen. However, I now offer some personal
experience that is in the opposite direction.
About 30 years ago I purchased quite a few 20 foot lengths of 5/8 fiberglass
rod to use in building a Quad. Of course, I soon found that this size is
too flexible to use as spreaders for 10 meters. I had to buy larger rod,
1/2 I think, to get the job done.
A friend came over and asked if he could have one of the 20 foot long 5/8
rods. He wanted to glue some 10 gauge solid copper wire to it and use it as
a vertical antenna. Although I cautioned him about the flexibility, he
tried it anyway. Needless to say, the rod easily bent over and the wire
became unglued in several places. He tried guying the rod but that was also
a failure. We laughed it off, and he left this on his roof for many years
with the rod bent over about double from its own weight and that of the
wire. The rod never failed. When he moved from Texas to California I
helped him take it down. It looked white from exposure to the sun, but was
not cracked at all. It seemed to have the same resilience as when
purchased.
Based on this experience, I can only conclude that your fiberglass rod had a
manufacturing defect. And I am wondering if the failure was a blessing in
disguise so that you did not put it into service.
Keith NM5G
-----Original Message-----
From: Tyler Stewart [mailto:k3mm@comcast.net]
Sent: Saturday, April 09, 2005 8:14 PM
To: Tom Rauch; keith@dutson.net; TowerTalk; Pete Smith
Subject: Re: [TowerTalk] polyrod
Let's hope that is true today, but it certainly wasnt true with the first
batches of the stuff we put up. It's been what...10 years or so since I put
together what may have been the first ever order from Polygon for hams and
it was a real PITA. Some of the coils sat around for a few months and when
we went to move them out, etc., we found lots of fractures and some complete
breaks. We had to trash a lot of it and they replaced it after we sent back
samples of the breakage.
If it were mine, I wouldnt let it set around a long time in a coil, no
matter what the sales people tell you. It's got to be stressful on the
glass fibers and the resin, especially if it's left out in the sun as a
coil. Black fiberglass gets very hot in the sun if it doesnt have air
circulating around it. Add the stress of being in a coil... no thanks!
The problem stems for the fact that glass fibers in compression are not very
strong, but very strong in tension, and the resin is just there to bind the
fibers together and adds no real strength. So when you bend a fiberglass
rod, the fibers on the outside of the bend are forcing the inside ones into
compression. Once the inside ones start to fracture in compression, it's
neighbors toward the outside start to fail as well... pretty soon you end up
with a major fracture or complete breakage...and you are trusting your life
to this stuff when you climb your tower. It's just not a smart thing to
do...dont tempt fate!
Ty K3MM
[snip]
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