CAD/CAM and Rubber molds

Jewelry Discussion
1

to all - seems as though there are quite a few folks using cad cam
machines and i am wondering if another aspect of this newish
tecnology is one that will bypass the mold process ? specificly if
the jewelry pattern is stored in cyber space does it need to be
stored in tradditional rubber mold form ? personally i would prefer
to cast an original wax than an injection molded wax because of my
own shortcomings over the nuances of controling injection wax in
highly detailed pieces. what are the cad cam users doing these days
using molds ? or storing patterns on disc ? or both ? thanks and
reconsidering my method existance

goo

2

We do both if it is a custom piece a one of a kind then it is store
as a computer file. If it is a piece that we are making several of
then we will rubber mold it as well. If it is a piece that we will
be making a lot of then we cut and aluminum mold for the wax but in
all cases the computer files a kept and once a month we burn two DVDs
of the files one for the bank box and one for a backup here as well
as the nightly tape backups I hope this helps

Rod

3

Goo-- At our shop, we still do a lot of mold making, especially for
items that we’ll most likely reproduce-- it’s much easier and less
expensive to inject a wax than to mill a wax. Milling is great for
one offs, but not so much for multiple items.

One of the new products we’ve just started working with are the low
temperature low shrinkage silicone rubbers. They allow you to make a
vulcanized rubber mold from a wax, so you can totally bypass the
step of casting your wax to make a silver master. Of course, your
mold is from a milled surface rather than a polished one, which can
be a disadvantage in some instances. So far, we’ve had super results.

Also, if you do a lot of production, the automated wax injection
systems, like the Rio Grande (I’m not a stockholder) Techtrol vacuum
assisted system work really great with the silicone rubbers.
Expensive system, but really great injection waxes.

Jim

4

Goo,

Cam milling is slow, and the results need some hand work before you
have a finished wax. I keep all models on disk, very useful if you
need a size 10 of a ring designed as a 6. Or sometimes parts of old
models can be re-used. I usually will just mill a second one but for
any more than that a mold is much faster. 20 minutes labour and a wax
a minute versus 3-6 hours of just mill time. Molds and shooting waxes
are a real time saver, the skills just need practice to learn, but it
is time well spent. There are very good reason that injections are a
standard industry practice for multiple production.

Jeff
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand

5

Hello Goo;

There are a number of reasons why you don’t want to cast with
CAD/CAM’d models. First, if they are cut on a mill, they take quite a
while to be produced, and they are a bit in need of further refining
in most cases (stepped effect from the cutting bit). Sometimes these
models are cut in a resin, which doesn’t burn out very well (although
there are new investments that attempt to correct that problem). The
built-up resin models, often referred to as “rapid-prototypes”, can
take a long time for the machine to produce too, and again, the issue
of residue left after the burnout process. So, because of the time
needed to build or cut the model, it gets expensive, unless you have
your own equipment. There is a new product called “HD” molding system
which works very well with an intricate CAD/CAM model. It’s capable
of reproducing delicate detail, although it’s a bit slower than wax
injection as it is an ultraviolet light curing resin. If you are
looking to do what I think you are interested in, I’d suggest some
designs will lend themselves to the less expensive milling process,
which can then be refined a bit by hand, and other designs, such as
with undercuts, will need the deposition/curing method. From that
point, that is, a fine prototype ready for reproduction, I’d get the
HD system. Gesswien carries it. It’s about as close to what you get
with a metal mold as I’ve seen, and metal molds are quite costly to
produce (again, if you’ve got the equipment, it’s not so much so).
MJSA has written a number of articles on CAD/CAM technologies.
Perhaps someone here knows what issues, off hand.

David

6

what we do is make a rubber mold from the first casting, however in
cases of intricate detail we will run a new wax since we keep all
the CAD files. this also serves to make alterations from the
original a snap.

april
CADesigner

7

While one can certainly store CAD files in cyberspace or on a disk,
that doesn’t substitute for an injection mold. Once you have a wax
master, made by milling or additive Rapid Prototyping, it’s usually a
good idea to cast it, finish it, and make a rubber mold by the
traditional process. This will allow you to make duplicates much
faster than by milling or growing new master waxes. Of course, you
may be making one-off jewelry originals, and have no interest in
editions. In that case, you can skip the rubber mold step, and simply
save the file digitally, or alternatively, make two masters while
you’re at it, and save one casting in physical form.

Andrew Werby

8

Hi David,

Sorry I have not had time to respond to your thoughts on the
Waxcutter system, I’ll try to address that subject as well as this
one about CNC waxes and molds.

Most of what I know about CAD/CAM has been learned from jewelers who
use ModelMaster CNC machines, so it’s been helpful to hear other
points of view on this subject. I was not familiar with the HD
molding system, so I will look into it.

Before I got into CAD, I worked as a craftsman for a couple of
custom- design shops here in CT. One did in-house casting and the
other sent out hand crafted waxes and metal prototypes to a casting
company. I preferred to clean up the outsourced castings because they
were cleaner and seldom had any porosity.This was not a reflection on
anyone’s casting skills. A professional casting house is more likely
to have the state of the art in casting equipment.

As Jim mentioned, going directly to a silicon mold from a milled wax
usually produces excellent results. What minimal shrink there is,
could be compensated by scaling up the CAD model by a few percent or
by adding a small fraction of a mm to certain dimensions of the
design
in the 3D drawing, if you thought it was necessary.

Considering the time it would take to make a mold, shoot a wax and
cast in metal, and the results that I would like, it seems to make
more sense to me to pay

$18 for a silicon mold and a little extra for the cost of the metal
alloy and get a very good casting delivered in 2-3 days. Since I
began
specializing in CAD design and modelmaking, I’ve found it’s a better
business decision for me to send waxes out to a casting house. I
chose Roni Castings, because they have a lot of experience with CNC
milled waxes and RP models… Roni recently did some castings for me
of
a medallion with intricate detail and lettering. As much as I trust
their work, the results greatly exceeded my expectations. Roni also
returned my milled wax in pristine condition after making the silicon
mold. Last night, my customer called to say she absolutely loved the
finished pieces, so when she orders more, I’ll call the caster…they
kept the mold, so I don’t need to send it back to them. If it’s a
one-off design and not a complicated model to mill, I don’t always
have a mold made.

Regarding the need to hand finish CNC milled waxes, yes, there is
some work that needs to be done, but the stepping effect that you
mentioned is not so much an issue depending on the machine and method
used to cut the wax…Surface quality is dependent on a few different
factors; the size of the tool chosen for a particular job in relation
to the detail of the model, the step-over of the tool and the feed
rate of the toolpath to the machine, all figure into the equation.
With a CNC milling machine capable of running a fast feed rate using
a
small tool, cutting with a small step-over without sacrificing
accuracy and repeatability, the time it takes to cut a wax and the
stepping effect or more precisely described, “tool markings” are not
so much an issue.

The light tool marks that can be seen with a loupe, are usually
negated by the level of surface detail that the regular casting
process can pick up and the normal finishing process. What I do
notice is that flat vertical sides of rings have some texture that is
better taken care of in the wax with a few passes of a sanding stick
or fine file, but I never touch the details of a design by hand after
the wax is milled. If I make a mistake by not telling the machine how
to do it right, I correct my error, and mill it over.

Intricate detail and symmetry with fine precision is the main reason
most people value CNC milled waxes, so if I’m in business to make
those kinds of models, why would I use a machine that can’t produce
those results? :slight_smile: I usually use a cutting tool with a tapered flute
(cutting edge) that has either a 7.5 or 5 degree side angle, so the
taper of the tool as it plunges down into a deep azure, cuts a hole
down with a smaller diameter at the base. The azures can be opened up
by hand with a drill before the wax is cast, or a separate toolpath
with a tool called a straight end mill can be done to fully bore out
the azures. ArtCAM has a CAM option which mills certain areas while
not gouging the rest of the model, so it takes 2-3 minutes for an
end mill to jump in and out of a bunch of azures… I love watching
the mill perform certain aspects of the milling process.

On the subject of the WaxCutter system, first I’d like to thank the
gentleman who clarified the question as to whether it can do curved
surfaces. I understand better now that a ring shank can be given an
over-all convex or concave shape. However, in seeing the finished
jewelry on the site, it is inapparently not used to create surface
modulation on small details.

A method of creating a ring with surface modulation on small details
from a flat template can be accomplished in Rhino 4

There are a few video tutorials here, *http://tinyurl.com/2uhf4u
*demonstrating the process. They are both under the topic- Rhino 4.0
WIP UDT Sporph, in the August 2004 section. You will have to sign up
with an email address for a password to view the videos, but they’re
worth seeing.

One tutorial shows how to flow a flat-drawn tapered ring shank to a
circle, in the other, a complex filigree pattern is flowed to a domed
ring surface…it looks like magic compared to the way we had to do it
in Rhino 3.0 ! :slight_smile: In another section, a twisted rope effect is
flowed to the edges of a shank.

I can appreciate the approach of choosing a CNC system that will
enable you to make money with it quickly. If you can learn the
WaxCutter system without a significant investment of time and effort
and it fulfills your immediate desired results in terms of simple
designs and meets your expectations of what a system in that price
range should do, then all the better.

I have an friend who just ordered one of the lower cost mills that I
guess some people categorize as a"hobbyist mill" but I am going to
reserve judgment until I hear how he does with it. Jewelry isn’t his
main source of income, so if he can produce a few models a week on a
mill costing under 3K, more power to him.

On your question regarding whether one needs to spend 30K on a high
end CAD/CAM system, it’s a matter of personal preference, balancing
financial considerations with immediate and long range goals and the
option for creative growth and expandability using CAD, towards the
future. Just as something to think about, Model Master has the Micron
mill for 11K which is compatible with all the conventional jewelry
specific CAD programs. So, if one got off to a running start now with
a Micron and MoI or Rhino, and purchased their choice of one of the
more expensive jewelry CAD programs later down the road, they would
still come in at about 10-12K less, have a reliable CNC machine that
would serve them well for years to come and do everything they’d ever
need it to do. Also significant is that they would not be locked
into a particular CAD program/CNC mill as with a 30K system.

Regards,
Jesse

9

Does anyone have any thoughts on whether a harder RTV mold is better for CAD CAM pieces or a softer one?
I’m thinking that very fine channels in many CAD designs might close off in a softer mold and fill better in a harder mold.

Michael