On Jan 25, 10:08*pm, Jeff Liebermann wrote:
On Sun, 25 Jan 2009 10:15:08 -0800 (PST), JIMMIE
wrote:
I came across an old single LPDA TV antenna in the trask. It was
pretty much FUBAR except for a coupe of feet of boom matrial and a few
insulators. My XYL is into making models and castings and she can make
a mold of the insulators easy enough. I was wondering if anyone knew
of a good casting material that would be compatable with the
requirements to build a single boom LPDA antenna to form the
insulators. She is not usually concerned with strength or UV
resistance so she couldnt help much on this part.
Nice idea, but all of my custom VHF yagi antenna insulators were
machined from black Delrin
http://en.wikipedia.org/wiki/Acetal_resin
or the cheaper Nylon 66. *However, they were all mobile transmitter
hunting antennas where UV protection and environmental survivability
were not an issue. *They only had to be more rugged than most yagis so
that when the antenna plowed into an overhanging tree branch or road
sign, the branch or sign would break, not the antenna. *Delrin should
be quite good, but rather expensive. *Nylon sucks as it absorbs
moisture and falls apart in the sun. *I used these simply because I
have a fairly good supply of both.
I've never tried to mold an insulator, but I can speculate on how it
might be done. *In my wasted youth, I repaired my surfboard with
various toxic and noxious epoxies that I suspect are suitable. *You
can purchase fiberglass matting and epoxy mix at any marine supply or
surf shop. *Instructions are on the can or the internet. *Machine a
suitable positive insulator, make a negative mold out of plaster, cram
it with epoxy saturated fiberglass stiffener, and pour in the
remaining epoxy mix (or something like that). *If ambitious, throw in
some additional reinforcing such as rusty nails, barbed wire, scrap
metal, or broken glass rod. *As long as they protrude the surface, the
presence of metal should not have much of an electrical effect. *If
you want to practice without the mess, try using Bondo or other
automotive dent filler. *It will be substantially more brittle but is
much easier on the nose and eyes.
You mention that your wife is into "casting". *I'll assume that
doesn't mean fly casting as in fishing. *However, there are a wide
variety of other forms of casting including operating a small foundry.
I've done this at home, amazingly without burning down the house:
http://www.backyardmetalcasting.com
I've made some unobtainable auto parts this way. *Somehow, I don't
visualize your wife doing all this, but it's possible. *There's also
sand casting, investment casting, plaster casting, lost wax casting,
and so on. *What manner of casting does she do?
--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558
Resins and plaster. Its something she learned to do in college and
once in a while she will make some dust collectors to give as gifts or
showsomeone else how to do it.
I always wanted tp try may hand at casing Al. Maybe one day when I
move out in the boonies I will get a chance. My father in law did it
but I think he got rid of all his equipment before he died.Hemade
mostly ornamental stuff and did a few demonstrations.
I think I will giveethe bondo a try. I have nearly a quart left over
from fixing a ding on the truck. I think it has some fibergass already
mixed in.
Jimmie