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.

Jimmie

"JIMMIE" wrote in message
...
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.

Epoxy and polyester resins come to mind. If you are rebuilding the TV
antenna and not adding significant weight, these should work well. Use the
low viscosity resins sold in quarts, and not epoxy glues.

For added strength, consider adding chopped fiberglass strands. For
reduced weight, glass microballoons may be added to the resins. They are
extremely light with a specific gravity of 0.18 to 0.25 depending on the
manufacturer. Phenolic microballoons are also available.

For ultraviolet protection, a small amount of titanium dioxide may be added
(1 to 5%), but the microballoons will do a fair job alone. Painting the
finished insulators with acrylic paint (Krylon®) will also provide good UV
resistance.

Many marine supply stores carry these resins, the chopped fiberglass, and
the microballoons. Be extra careful with the polyester catalyst (typically
methyl-ethyl-ketone peroxide) as it is extremely damaging to the eyes.

Good luck with your project.

73, Dr. Barry L. Ornitz WA4VZQ
[transpose the digits to reply]

NoSPAM wrote:
"JIMMIE" wrote in message
...
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.

Epoxy and polyester resins come to mind. If you are rebuilding the TV
antenna and not adding significant weight, these should work well. Use
the low viscosity resins sold in quarts, and not epoxy glues.

For added strength, consider adding chopped fiberglass strands. For
reduced weight, glass microballoons may be added to the resins. They
are extremely light with a specific gravity of 0.18 to 0.25 depending on
the manufacturer. Phenolic microballoons are also available.

For ultraviolet protection, a small amount of titanium dioxide may be
added (1 to 5%), but the microballoons will do a fair job alone.
Painting the finished insulators with acrylic paint (Krylon®) will also
provide good UV resistance.

Many marine supply stores carry these resins, the chopped fiberglass,
and the microballoons. Be extra careful with the polyester catalyst
(typically methyl-ethyl-ketone peroxide) as it is extremely damaging to
the eyes.

Good luck with your project.

73, Dr. Barry L. Ornitz WA4VZQ
[transpose the digits to reply]

Where do you buy the titanium dioxide?
73,
Tom Donaly, KA6RUH

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 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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.

Jimmie

I think before I went through that hassle I would just buy some solid
fiberglass rod and make them out of that.

www.mgs4u.com as one example sells 8 foot lengths of half inch rod
for $6.00.


--
Jim Pennino

Remove .spam.sux to reply.

Jimmie,
Another 2 cents worth - you could try something like "Bondo" which is
resin-based body filler. - Pick it up at Auto-Zone or other Auto parts
place. But well-coated wooden blocks may work ok as well. I would try to
find a way to use a PVC fitting to save money.
Hal W4PMJ

"JIMMIE" wrote in message
...
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.

Jimmie

"Tom Donaly" wrote in message
...
NoSPAM wrote:
For ultraviolet protection, a small amount of titanium dioxide may be
added (1 to 5%), but the microballoons will do a fair job alone.
Painting the finished insulators with acrylic paint (Krylon®) will also
provide good UV resistance.

Where do you buy the titanium dioxide?
73,
Tom Donaly, KA6RUH

I was sent 10 pounds from a friend at DuPont, one of the larger
manufacturers of titanium dioxide. For small quantities, I would suggest
contacting a local paint manufacturer, or artist supply store. The pigment
is used in many ultra-bright white formulations. Note that titanium
dioxide has a high dielectric constant between 85 and 110 depending on the
ratio of rutile to anatase. So to minimize detuning effects of the
insulators, use them only at low impedance points of the antenna.

73, Dr. Barry L. Ornitz WA4VZQ
[transpose the digits to reply]

"Hal Rosser" wrote in message
...
Jimmie,
Another 2 cents worth - you could try something like "Bondo" which is
resin-based body filler. - Pick it up at Auto-Zone or other Auto parts
place. But well-coated wooden blocks may work ok as well. I would try to
find a way to use a PVC fitting to save money.
Hal W4PMJ


While Bondo is based on an unsaturated polyester resin, it uses lots of
styrene and filler materials. Both destroy the inherent strength of the
polymerized polyester. Stick with a high quality boating resins and use
fiberglass for strength.

73, Dr. Barry L. Ornitz WA4VZQ
BLOrnitz84@charter/net [transpose the digits to reply]

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

On Sun, 25 Jan 2009 23:29:58 -0800 (PST), JIMMIE
wrote:

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.

I mentioned Bondo only so that you could practice before switching to
epoxy resin and fiberglass reinforcing. Bondo is brittle and will
crack.

However, the polyester resin she is currently using might work with
the addition of some stiffener. Get some fiberglass matting and try
using her resin to mold an insulator. The stuff is not really
suitable for electrical or outdoor use, but might be worth testing
since you have some. Remember, the strength is in the fiberglass
matting or rod stiffeners, not in the resin.
http://www.tapplastics.com/shop/product.php?pid=75

If it doesn't work, at least you'll have the most colorful antenna
insulators in the neighborhood. Maybe imbed some LED's or neon lamps
for a Christmas tree effect.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558