Ed Huntress wrote:
"JohnM" wrote in message
m...

Jeff Wisnia wrote:



The question tickled my memory, as I used to work at my dad's jewelry
manufacturing plant in the late '40s. We used the traditional spring
wound centrifugal casting machines to make lost wax castings of all
kinds of jewelry pieces in gold and platinum alloys. Our machines were
set in the center of big round galvanized iron washtubs to catch the
splatters if things went wrong.

Molds for those precious metals were made from a plaster like
"investment" material (Inside metal rings, like you mentioned, just
2-1/2" diameter by 3" long pieces of thin wall steel tubing.) and were
transferred with tongs to the machines and "shot" full of molten metal
while still hot from the wax "bake out" furnace, which IIRC brought them
up to a dull red heat. That helped avoid "cold shots" caused by the cast
metal chilling before it fully filled the mold.

Silicone rubber wasn't around then, but we did use rubber molds to
"shoot" the wax patterns in. Those molds were natural rubber vulcanized
in a heated press around a metal "original". They were carefully cut
open with an X-Acto knife to release the original and create the wax

mold.

Dad learned his jewelry craft in Germany BTW, circa 1918-1921, before
emigrating to the USA. His half-brother Leo was a Dentist in Dresden and
stayed their until dad helped him and his family get to the USA in the
nick of time in 1939.

Uncle Leo was also skilled in lost wax casting because back then most
dentists had to cast and finish their patients' bridgework themselves,
just like the jewelers did. He worked in dad's jewelry factory through
WWII and also did some unlicensed family dentistry in the apartment he
and his wife lived in. I think he treated almost everyone in the family.
I still remember him drilling away in someone's mouth using his foot
treadle powered drill with it's articulated belt drive system.

Leo once proved before my own eyes how he could make a lost wax cating
without a centrifugal machine by tying a cord onto the mold, melting the
metal in the sprue hole and then snatching that cord and whirling the
mold around his head in a circle. Wowza! That's something I'll never
forget, that and the time I saw a crazy physicist from Cornell
University toss down half a paper cup fill of liquid nitrogen, followed
by his emmiting the longest belch you could imagine.

Back on topic again, there's a quite good thread on the stuff you're
looking for running now on the HSM BBS:

http://bbs.homeshopmachinist.net/For...ML/011810.html

Jeff


Very cool stuff, Jeff. I like that mold-on-a-rope trick, never heard of
it before.

John


You'll see it described in some old casting books. It's dangerous but it
works.

Another dangerous trick that works, again from the jewelry business, is
"diecasting" precious metals into a plaster mold, using a wad of wet
newspaper for a diaphragm. You have a pool for the metal cast into the top
of the mold and a short and narrow sprue leading straight down to the mold
itself. You fold up about 1/2" of wet newspaper into an 8-in.-square wad and
soak it. When you pour the metal into the pool, you immediately lay the wad
of newspaper on top of it and slap it with your hand.

This is a good way to splatter molten metal onto yourself and suffer
permanent damage. My uncle was an expert at it. He wore a full-face o/a
welding shield, a leather welding jacket, and leather welding gloves. He
didn't used to, and he had some interesting scars as a result.

--
Ed Huntress



Yeow.. I'd like to see that done. What's the purpose? To ensure filling
a cold mold?

My favorite is a lost-wax process where the pattern is left in the mold
and the mold and casting material is enclosed in a clay egg.. Put it in
the fire with the mold up and you get the burnout, wait 'till the thing
is hot enough that you know your metal has melted and turn it over and
the metal enters the mold. That always seemed like a cool way to do things.

John