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Patching Castaldo rubber mold?


#1

I bought several lots of rubber casting molds on ebay recently. One
of them is a really lovely, large bead cone that I would really like
to cast for my own use. Problem is, part of the core of the cone is
shredding, and it’s causing the mold to fill quite poorly (which is
probably why it ended up on ebay…). I can’t get even one good wax
out of it. They all come out with thin spots and holes where the
rough shredded core comes in contact with the sides of the cone.

Is there anything I can use to smooth out the rubber core and hold
it together at least long enough to get 3 or 4 good waxes so I can
reproduce the cone?

Speaking of molds, in the lots I bought were about 100 molds of
items that are meant to have small faceted stones set in them–things
that look like parts to be assembled, not complete jewelry pieces. I
don’t set stones, so I don’t know the correct names for any of these
bits and parts. I’ll never use these, so I’d like to sell them. If
anybody might be interested in them, e-mail me privately.

Kathy Johnson
Feathered Gems Jewelry
http://www.fgemz.com


#2
a really lovely, large bead cone that I would really like to cast
for my own use. Problem is, part of the core of the cone is
shredding, and it's causing the mold to fill quite poorly 

Maybe you could clip out the core, inject the mold as a solid piece
without a hole in it, and re-drill or mill the wax core again, to
get a wax of the original shape. Then cast that, and make a new mold.

M’lou Brubaker
Minnesota, USA
http://www.craftswomen.com/M’louBrubaker


#3

My first try would be to try to shoot it with out the core at all and
try hollowing out the wax using progressively smaller ball or bud
burs, if I understand the design correctly. Hold it up to the light
to see how thin you are getting it. Alternatively and what I would
probably do if it won’t work without the core is to trim the sides
of the core with a mold knife or even side cutters. You can use a hot
wax spatula or knife blade to smooth out the rubber (works better
with some types of rubber than others), but it’s a nasty smelly
proposition.

Dave


#4
You can use a hot wax spatula or knife blade to smooth out the
rubber (works better with some types of rubber than others), but
it's a nasty smelly proposition. 

Yes, I believe this is called “burning in” a rubber mold, and I have
done it at times to correct small details. I do it with the red-hot
end of a solder pick or nail. This used to be a more common practice
to create sprues or gates into the mold, but everyone uses solid
metal gates on their models now. This might help for your core, but
it will make the metal wall of the bead cap thicker, and you will
end up having to correct your wax, anyhow. I guess you could try it
before just giving up and cutting out the old core. Vent the fumes
away from the bench with active suction, or do it outdoors.

M’lou


#5
Maybe you could clip out the core, inject the mold as a solid
piece without a hole in it, and re-drill or mill the wax core
again, to get a wax of the original shape. Then cast that, and make
a new mold. 

I somehow neglected to mention that the piece is curved, quite
narrow, and about 1 1/2 inches long. It looks rather like a long
curved twisted trumpet flower. I don’t think I can carve out the
entire inside of a solid piece of this shape. I’m not that good at
carving… Perhaps I could cut one in pieces and hollow it out, then
reassemble it, but that sounds like more work than the piece is
really worth.

After much trial and error, I managed to get two waxes from the mold
that had relatively few holes in them. I spent some time building up
the holes and thin spots until they looked pretty good. I promptly
ruined one with the butane wax smoothing tool by glancing up when
the dog barked at something. :’( But one wax survived, and I plan to
cast it this weekend. Maybe fortune will favor me.

Kathy Johnson
Feathered Gems Jewelry
http://www.fgemz.com


#6
I somehow neglected to mention that the piece is curved, quite
narrow, and about 1 1/2 inches long. It looks rather like a long
curved twisted trumpet flower. 

Sounds like a job for a curved shank bur. That’s one of those
inventions I keep hoping someone will come up with. That and a girdle
stretcher, a diamond magnet and a graver handle with spell check and
auto-scroll.

Glad to hear you’ve got it working well enough to get at least one
for a new mold.

Dave


#7

David,

a graver handle with spell check and auto-scroll. 

What a great invention that would be, along with an Engraving Eraser
(better than a burnisher) for those words spell check said were
right because they are right in a different context.

Paul