I have designed some 4-8mm sterling silver metal beads that I want to
make rubber molds for so that I can repeat them by using the lost wax
casting system. My problems that I will have is that when I vulcanize
the rubber how can I retain the hole in the bead for the bead wire? I
don’t want to redrill the hole in wax for each bead. Is there a way
that in the rubber mold a can suspend a piece of metal wire so that
when I inject the wax that I can remove the wire to ensure that I
retain my hole accurately or is there another technique? My second
problem that I forsee is how can I retain the hole while doing the
investment process? I plan on making a large amount beads at one
time, so efficiency is required. Any help is appreciated greatly.
Hi Joel,
I do a lot of these, very successfully. Put a piece of stiff wire in
the mould, use piano wire or titanium, I use 1.6mm mostly, it needs
to be highly polished and make sure that the section where the bead
goes is straight. The far end away from where you inject is bent
around in a ‘u’ shape and when you cut open the mould you stop
cutting before you get to the ‘u’. The mould therefore stays in one
piece, with keys cut only at the front and the wire poking out from
the uncut part.
When you extract the wax twist it slightly to ease it off. A little
mould release wiped on the metal rod occasionally will help.
For small beads, 4mm, run the sprue down to one side of the wire
core, for 8mm you would probably be better doing two sprues, one down
either side. The principle is that you flow the molten metal along
the length of the plaster core rather than at right angles to it, so
as to put less stress on it.
I have enjoyed learning about this, I now do long thin beads, large
hollow beads cast in one piece, and curved holes through. I would
recommend a stereo microscope for the finest detail.
I have though about writing up my methods, everyone else seems to be
writing books! I just thought it was a bit of a niche in a niche,so
only a very small audience, you really also need to do your own
mouldmaking, wax injecting and casting.
kind regards Tim Blades.
My problems that I will have is that when I vulcanize the rubber how can I retain the hole in the bead for the bead wire?
I have done this many times. A small piece of piano wire the
diameter you want to hole, make a right angle bend for ease of
removal, you have something to twist as you pull it out. After you
make the mold, you need to grind the mandrel shorter as the mold
shrinks. You do need to use something to clean the investment out of
the bead hole once cast. I have done small diameter tubing and hinges
successfully. If you need more help, email offline.
Richard Hart G.G.
Jewelers Gallery
Denver, Co.
Is there a way that in the rubber mold a can suspend a piece of metal wire so that when I inject the wax that I can remove the wire to ensure that I retain my hole accurately or is there another technique? My second problem that I forsee is how can I retain the hole while doing the investment process?
Your instincts are correct in respect to the wire and rubber mold
technique. This is what my rubber mold makers do when I have hinges
that have to be molded, so it will definitely work for your beads.
One thing I was going to try on some beads I make is to try to plug
the hole in the wax with graphite pencil rods. I’ve not tried it. My
concern is that the clay that is mixed in with the graphite won’t
hold up in the casting process, but to be honest I don’t know. I’d
like to have tried it. I was never able to locate pure graphite.8mm
rods. You’d still have to drill out every bead to remove the
graphite, so you lose some productivity there, but it’d be faster
than drilling the whole thing out.
Larry
Cary, NC
I have enjoyed learning about this, I now do long thin beads, large hollow beads cast in one piece, and curved holes through. I would recommend a stereo microscope for the finest detail.
thanks Tim. a very helpful post. would you explain a bit on how to do
the curved holes through? also, perhaps any tips on how to do long
thin beads?
Andrew
This is an easy problem to solve. I cast these all the time. Take a
wire the diameter of the hole that you want to pierced thru your
bead. Run that wire to the edge of your mold frame. Vulcanize it and
then cut a little crater exposing the wire where it ends at the side
of the mold.
Now cut your mold in half. Remove the pin from the bead and place it
back into the rubber mold.
When you inject the wax bead remove the wire before you separate and
liberate the wax bead.
When investing (under high vacuum) handle the flasks with care. When
they have been properly burned out be careful NOT bump them or you
will chance breaking the little pin of investment that is now
suspended within the negative space of each bead. Vacuum cast (do
not use centrifugal casting) as this is the gentlest way of getting
the metal into the flask.
Jonathan Russell
JR Casting
SF CA 94124
415 671-0120
Vacuum cast (do not use centrifugal casting) as this is the gentlest way of getting the metal into the flask.
I have done production casting for jewelry artists who made beads and
I used centrifugal casting with no problem.
Richard Hart G.G.
Jewelers Gallery
Denver, Co.
Vacuum cast (do not use centrifugal casting) as this is the gentlest way of getting the metal into the flask. I have done production casting for jewelry artists who made beads and I used centrifugal casting with no problem.
Ditto.
Centrifugal casting gets the metal into the flask with more force,
and faster, so fully filling fine details is more assured. On the
down side, there is more turbulance in the metal, which can affect
porosity, and if you torch melt, it’s a bit easier to get flux
inclusions in/on the castings. And of course, with larger flasks and
quantities, there’s the whole safety thing of a spinning centrifuge
potentially throwing molten metal around the shop if something goes
wrong.
However, for me the big difference is casting temperature. I find
that with most metals I cast, I can use a flask temperature sometimes
200 degrees cooler than I’d use with vacuum casting. That gives a
finer grain structure to the metal which sometimes is a big
advantage.
Peter
This suggestion may not fit your designs, but if you put some holes
in the walls of your beads, even small ones, they will really help
support your investment core.
M’lou