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Cutting rubber molds


#1

Does anyone have a good source of for cutting rubber
molds?

Best Regards,

Randall Brooks
@Randall_Brooks1


#2
    Does anyone have a good source of for cutting
rubber molds? 

The Rio Grande two tape video "moldmaking for jewelry #560-045
$99.95 Jesse


#3

Randal

I do not cut my molds anymore. it’s a waste of time and you gonna have
to sacrifice a big bunch of them trying to make the parting line right
in half of the model. My advice is don’t try to play the professional
and go to the best alternative for beginners which is powder
separation.

Ask Michael Knight at Castaldo and he would give you a good tip on
which rubber component is better. I just received some locks and
separator cream from him free of charge. Since I learnt the
powder�separation process I haven’t cut molds anymore. Marco.M at
Silverado


#4

Hello, greatly respected members of the forum! My name s Varvara, I
m 16 yrs old and I m only beginning doing jewelry. You can see me at
my bench at:

http://www.ganoksin.com/orchid/BenchExchange/jeweler-bench-9.htm .

Here’s my question. Could anyone tell me, if there are any articles
online where I can see and read how to cut rubber moulds properly. In
my family everyone does jewelry. We all help each other, and that s
really very interesting. We make very complicated carved details
empty inside. We have to cut the mould to a lot of pieces in order to
take out the wax. Then, when the rubber mould is brought together, we
often get a wax with displacements or with wax overgrowth. And we
need great accuracy. Thanks in advance!

Varvara Shmid


#5

Varvara Castoldo at one time sold a tape of mold cutting. It is very
good and helped me many times over the years. I am not sure if it is
still available but I would check with them. Jerome


#6

Varvara,

It seems to me that the complexity of your piece is working against
you, and it may be that you would be better off to do each item
separately, anyway. Here’s a thought, though: if you were to cut
the piece in half, at some arbitrary point, could you mold those
halves individually with less trouble? Then, cast your wax in them
and bring the two resulting wax castings together to form the
original shape again.

I know practically nothing about casting or wax work, by the way…

Loren
http://www.golden-knots.com/


#7

Varvara, Here is a another thought. Perhaps you should try a rubber
mold of the exterior of the piece and use a wax pen ( I use one
designed along the lines of a batik wax pen) to build up a layer of
wax on the surface. This eliminates air bubbles on the surface. You
can then pour hot wax in the hollow center and wash it around until
it builds up a sufficient thickness on the sides. I have a mold of a
snake that I have to do this way. The detail of the scales is just
too fine for the wax to fill without bubbles and I don’t want any
seam lines to mar the detail of the scales. It takes longer than a
wax injector but you get all the detail and no seams on a hollow
form. If you cannot access the interior of the mold with a wax pen
you may have to do a mold that is a very thin layer of rubber and
back it with a plaster of Paris jacket to make the rubber mold hold
its shape while empty. You pour the wax into the interior of the
mold and create a thin layer of wax in the mold by washing the wax
around in the interior as the wax cools. When the wax is thick
enough you pour off the excess wax and let the wax in the mold
harden. When the wax is hard remove the plaster jacket and peal the
rubber mold off of the wax.This technique provides a hollow form
without seam lines. This process only works on very simple hollow
shapes which do not create mechanical locks however, surface detail
can be very intricate and complex. It might help if you can give us
a dimensional description of the piece or even a photographic image.
I hope my explinationexplanationenough. Frank Goss


#8

Hello,i need about cutting rubber molds,i have books but
the of this books is smalll.i need about the
cutting in zig-zag,i need photos to see the complete method of
cutting,i want to read articles about this.please i need this for
start to cut in a correct form.thanks for the help.thanks very much


#9

Dear Nardon Lopez, This is Michael Knight at CASTALDO rubber. I am
sorry to report that there are really no books or video tapes on
rubber mold cutting that are worth anything. We tried back in the
Betamax days and have finally disposed of our last copy. We probably
will do something one day, but for the moment the best thing is to
find an experienced moldmaker – even if you have to travel far –
and pay him or her to teach you. There are so many variables,
tricks, tips, techniques, etc. that only watching a master at work will be of much help.


#10
I am sorry to report that there are really no books or video tapes
on rubber mold cutting that are worth anything. 

I always sorta like the substantial chapter in Murrey Bovins classic
book, “Centrifugal or Lost Wax Jewelry Casting”. Sure, there are a
lot of things it doesn’t fully cover, and more than a few things that
are outdated. But in general, it seems to give a pretty good
discussion of at least the basics and general practices of mold
cutting. If you “read between the lines” and study the photos as
well as reading the text, you’ll get additional ideas. Not much
there for an already experienced mold cutter to gain additional info
from, but certainly, for a beginner, it’s a good start.

But of course, as you say, working with an already experienced mold
maker will teach someone a whole lot more, and a lot faster, than a
book. And, as you also say, there are myriad variations on
technique. I don’t think there are two mold cutters out there who
actually would cut a mold exactly the same way. Everyone has their
own subtle favorite tricks and methods, and with a bit of practice,
almost any variation on the basics can be made to work. The rubber
is pretty versatile.

for the original poster, the question of parting lines in the wax is
a universal one. You strive to minimize their impact on the wax
model by cutting the parting lines either where they will be easy to
clean up, either in the wax or the finished metal casting, or by
trying to put the cuts right along edges of the piece, where they
then really don’t show as lines. Take care also that you don’t cut
the rubber into very thin flimsy sections which can shift inside the
mold when it’s injected. (With some complex molds, this is hard to
achieve, but careful planning of where the mold will be cut usually
can find good solutions. Sometimes, especially when you’re learning,
it’s necessary to make several molds of a piece before you figure out
just exactly the best way to cut the mold.) Whatever you do, be sure
also that the mold halves are well “keyed” to each other. I "wiggle"
the mold knife in a small “zig zag” motion whenever cutting rubber
areas that are away from the actual model, so the rubber there is cut
in wavy hills and valleys, and the whole mold surfaces lock in place
to each other. This helps prevent misaligned areas in the wax
injections.

If you have a mold that is persistently giving you fins and parting
lines, then you should also take care to examine your injection
technique. Maybe you’re clamping or hold the mold too tightly,
deforming it, or not tightly enough, letting the halves of the mold
separate from the wax pressure. And often, beginners tend to use too
high a pressure on the wax injector. You usually don’t need more
than 5 or 6 pounds of pressure on the wax, and often less. Using the
least pressure that will still fill the mold will minimize parting
lines and fins formed by excess wax pressure. If you have a mold
that requires higher pressure to fill completely, you can also look
at the mold and determine whether the problem isn’t actually not
having enough vent cuts in the mold. A lack of vents in some details
then needs you to use much more pressure to inject the mold and get
blind details to fill. Vents can themselves give you parting lines,
so be careful with this. Experience will teach you what you need.
Also, pay attention to the temperature of the wax. Too cool, and
you’ll need more pressure, perhaps causing problems. Too hot, and
not only will the wax tend to stick to the mold, but you’ll get much
more shrinkage problems in the wax, with things like sunken areas in
flat spots, and the like. This behavior is also much influenced by
just which type of wax you use for injecting the molds.

Hope that helps.

Peter Rowe


#11

Karen,

I believe you may have it backwards. With my very small and
arthritic mitts, I changed from the normal rubber to the silicone
type, because They could be powder-separated. They are wonderful !!
Have also never had problems with lack of the inner cut locks. That
might be because I don’t have many complex molds nor need high
injection pressure. Am sure the vulcanized rubber must be used best
for some things though. But I’ll never go back to cutting.

Pat


#12

Pat,

I’d love to know more about how you’re doing this and what you’re
using as a separation agent. Both the Kerr and the Castaldo people
told me at the last MJSA that you couldn’t powder-separate silicone.
If you can, that would be the best of both worlds!

Karen
@Karen_Goeller
Hand-crafted artisan jewelry


#13

Dear Karen,

This is Michael Knight at CASTALDO.

I’m sure what I must have said was that you could not use the powder
separation technique with LIQUID rubber compounds because the
powder or cream would wash away. Yes, you CAN use it with
VULCANIZING OR NON-LIQUID RTV mold materials.

Michael


#14

Karen, my silicone sheet and the separator came from Contenti. They
were selling fine mica powder with it. I rather doubt they still use
that, as I’ve heard talc is now used. You simply make a pounce bag of
muslin or similar filled with it, top twisted with rubber band for a
handle, and dab it on the mold surface with the item to be molded in
place, plus whatever you’re using for lock registers, before
vulcanizing. My mica powder turned out to be a lifetime supply I
think. Haven’t made any molds for quite awhile, since I’m in
semi-retired category and mostly teaching. There is no vulcanizer at
school, so I only talk through the mold making process and give ways
to make them with minimum heavy equipment, then suggest for starters
they have them made locally or elsewhere. No problems have been
reported back to me.

If I had the time and energy, which I don’t now during a period of
acute stress and sadness, I’d go through the other catalogs to see
what they’re offering. I know Rio has the silicone material which is
the similar brick red color of mine - which I believe was the first
out from Contenti. Saw them demo in Providence at an Expo. Sure
appealed to me! Never regretted the purchases either. And they’ve
aged very well, stored in dark, dry, cool area. Keep all molds in
those conditions and they’ll live long and prosper. You too. Good
luck with non-cut molds. Think you’ll approve. But, I was warned not
to use the same mold frames you use for the regular rubber, thus I
also have dedicated frame plates as well. Recently I saw a post from
Tas, if I’m not mistaken, telling of Daniel Grandi doing a demo with
this material, and using the mica powder, at Metalwerx. You might
want to check with him too. Hope this helps.

Pat