CAD/CAM grown model woes

Jewelry Discussion
1

Enlighten me please.

I have resisted using Cad Cam preferring what I knew. I recently had
a job, thought I would make my life easier. Sent the picture of a
ring to a Cad Cam guy.

Got a nice grown model back. Gave it to my caster, a very
knowledgeable whlosesale jeweler I have worked with for 15 years. I
asked him to call the Cad Cam guy and get specifics of how to burn
out
as there are issues with ash from this material.

Since I am in the middle between new technology and old school, I do
not want to be part of the problems with new technology and new
problems. My caster followed the directions, and the casting came out
with a loss of detail where the ash remained. My caster had suggested
to make a mold from the grown model, I said I would like to avoid
that, but if it was necessary, do it that way.

Theoretically my caster following Cad Cam guys advice should have
produced good results. My caster relied on the CAD CAM guys info to
use the model and avoid problems. . Caster had to laser weld to fix
problem I would not have if I had a wax carver make the model.

So, in the future, make molds of the grown models? There was no
saving of time or money using CAD/CAM. Just a new problem. How you
those who use grown models deal with this?

Richard Hart

2

Richard,

So, in the future, make molds of the grown models? There was no
saving of time or money using CAD/CAM. Just a new problem. How you
those who use grown models deal with this?

The material used in SolidScape rapid prototyping systems burns out
like any ordinary wax. No special procedures or kiln killing high
temps required. When you go shopping for a service bureau ask what
machines they’re using.

Les Brown

3

What kind of wax is used for “grown models”? Does the wizard wax
(orange stuff) have a high ash content ? Please let us know about
this wax and what can possibly be used as a substitute.

Margie
www.deepdetail.com

4

Richard,

To start, I am no way associated with any of these printers/ growers
other than being a user of their respective products.

There are a few different systems out there used to grow models from
a CAD design. Yours sounds like a resin model from a particular
(unnamed) company’s machine which is notoriously difficult to burn
out completely (even though they claim it to be and even issue a
recommended burnout schedule with th models) without getting porosity
or “cauliflower” textured surfaces on your castings. There has been
some speculation that a rapid burnout cycle (presented at the 2007
Santa Fe Symposium) will give improved results in casting; but
experience (mine and others I correspond with) show this process to
require a specialty high strength investment and, yet still, the
results are only somewhat improved and only in smaller or lighter
weight objects. For now I recommend molding of any of the resin built
CAM models and then casting a wax (or a HD ^TM ) injection from
there.

There is one model printer (contact me off line for the info) that
produces a wax/polymer model that can be cast directly with results
every bit as good as casting a regular wax model. The printed
resolution of these models seems to be every bit as good as the
others that I have tried (and in some cases, even crisper).

Beyond printing/growing, there is milling as a possibility for
producing your model; provided that your model is compatible with
the method.

5 
Got a nice grown model back. Gave it to my caster, a very
knowledgeable whlosesale jeweler I have worked with for 15 years

Richard, I don’t know much about the growing side, and those
materials, but someone gave us a handful of grown pieces to cast a
couple of months ago. What a nighmare it was, and we never got
anything you’d call a clean casting. I had suspicions, so I put a
piece in water over the weekend and discovered that it was partially
soluble in water. It was also quite brittle. This material was a
pretty kind of teal color. According to the client, who’s the CNC
guy, this was the latest material that solved all the casting
problems of previous ones and it should cast just like wax and yadda
yadda. To me, when you factor in that he’s talking $150/model
minimum - that’s just machine time, and then throwing in $45 for an
RTV mold, well — never again, for me. I paid $85 for a shared prong
wax that was milled, which is way more like it. I’d likely machine
the outside and then do benchtime to get the stuff that RP is needed
for, if anything.

6

Richard,

How you those who use grown models deal with this?

I think your problem began by asking someone who has never burned
out this material to cast successfully with from someone
who doesn’t cast.

I have cast resin models and printed models. I’ve always followed
this burnout formula as set out by Ransom and Randolph for the
Ultravest investment:

Initially hold the flask at 300 degrees for 2 hours
elevate to 700 over 2.5 hours
hold at 700 for 2 hours
elevate to 1350 over 3.5 hours
hold at 1350 for 3 hours
reduce to casting temp and hold for a final cycle of 1 hour

This is for small flasks not over 2.5" in diameter. For medium sized
flasks up to 4" in diameter increase the initial and final hold
temperatures an extra hour.

Initially I had reservations with such a long burnout for small
flasks, but it has never failed me. Perhaps you can pass this on to
your caster for subsequent jobs.

Hope this helps.
Larry

7

What I have experienced so far is that none of the photopolymer
resins burn out in a trouble free fashion. They are hydroscopic and
absorb water from the investment causing surface problems and
swelling of the model and some have a fair amount of ash residue.
There are certainly people that are claiming good results from the
photopolymers but I think it is still too much an art and not enough
a science involved to just hand a photopolymer model to a caster that
is not experienced with them and say “just follow the instructions”
and all will be fine. I think despite the hype from the vendors that
the photopolymer patterns are still best used as a pattern to be
molded then injected in standard wax. I find the wax jet type
patterns grown on the Sanders or Solidscape machines still are the
best for direct burnout but they still have too much pixelation of
the surface for me to be happy with them. My CAD/CAM preference is
definitely to use milled patterns unless there is no way to mill the
model. Milled patterns have far less cleanup required than even the
best of the grown patterns.

James Binnion
@James_Binnion
James Binnion Metal Arts

360-756-6550

8

Richard,

The great advantage of the additive prototyping (“printing” or
"growing") process is that a number of models can be "grown"
simultaneously. That process can take as long as 12-15 hours,
depending on complexity and number of models, but there can be great
economy in doing so. However, using additive protoyping methods to
grow single models is usually not cost or time-effective.

I worked with the technical team from 3D Systems when they were
bringing their version of the technology to the jewelry market. It
became obvious that casting problems had to be addressed.

To oversimplify (!), we discovered that great care had to be given
to all stages of the casting process. Choice, handling and
preparation of investment medium played an important part. Over the
years, investments have become so “good” that many casters have
knowingly or unknowingly taken “shortcuts” in their traditional
casting routines. Unfortunately, the “idiot-proofing” features of
many modern investing materials are no guarantee when it comes to
burning out the various rsins and plastics used in the growing
technology.

We concluded, at the time, that higher burnout temperatures and
longer than “normal” dwell times were needed for the materials we
were using at that time. This finding seems to be consistent across
the board, still, as far as I know.

It was interesting to note that many users were looking for a “magic
bullet” that would solve all their modeling needs. More bluntly,
armed with this new hammer, every job began to take on the
appearance of a nail, and with the usual results! Often, the best
use of the growing machine is to not use it.

Now, the best solution to dealing with the near-ubiquitous ash is to
blow it out of the hot investment with an air gun, then return the
investment to the furnace for a minute or three to assure an even
re-distribution of heat before casting. I know what you’re thinking,
but there has been no damage to the investment after doing this many
thousands of times. Sounds crazy, but it works.

Wayne Emery

9

Richard

This specific problem you describe sounds like an incomplete
burnout. I would guess that the caster may have consulted the grower
but did not follow instructions in detail, and if the instructions
are not followed in detail, the casting will fail.

The different resins have different castabilities, And several are
very castable"Invision HR, Perfactory", We have found no ash content
in Invision HR resin using a full burnout process. Some are castable
but with a bit of work around(Viper). We cast primarily Invision HR
resin. Of note is that we often cast hand carved waxes right along
with the resin with equal success.

There are very specific steps to take in casting the materials. A
caster must want to change some steps to have a successful casting of
resins. Most failures occur because the caster will not adapt the
process to the material, they insist on using methods that work with
wax, but just wont work with the newer materials. Skipping any of the
steps will definitely result in failure.

It took us a bit of trial and error to dial in casting of resins.
From experience, the biggest problem is the investment and then the
burnout. I will briefly cover some of the primary details of the
process.

Sprueing:

Sprueing is the most overlooked part of casting in many cases, A
smooth transition from the sprue to the piece to be cast is
essential. The piece needs to sprued at its heaviest section, general
sprueing techniques apply here.

Viper models are castable but need a extra blowout sprue to assure
full cleanout of the cavity, there is the possibility of ash in viper
models. Prior to casting, the cavities are blown out with compressed
air to make sure all Viper residue is gone

Investing :

The choice of investment is one of the most critical steps in the
process. We have tried many investments and many processes. These
steps work consistently in our production. We use “Doc’s Plaster”
from PM West for all resin casting, it works for gold silver and
platinum we follow the directions as specified by the manufacturer.
We use the rubber flasks as supplied by PM West for investing. For
smaller castings we use a yoghurt cup that we cut the bottom out of.
We do not use a metal flask, all castings are done “flaskless” Its OK
to use a debubblizer solution.

Yes, the investment costs more than regular investment, but getting
the casting right every time is worth it.

Burnout:

We burn out with an electric oven with a programmer. ( Gas ovens
naturally have enough oxygen to get a good burnout) We have modified
the oven by drilling four holes into the kiln at floor level, equally
spaced. We drilled about 1/4 inch holes. To increase the ability of
the oven to truly burn out the resin, the oven needs more oxygen.

To create the proper burnout, We use an old aquarium bubbler as an
air supply. We attached about a foot of quartz tubing to the plastic
hose and insert the quartz tubing into one of the holes we drilled.
This is probably the most critical step in burnout, electric ovens
do not have enough oxygen circulation for a good burnout. Heat alone
will not fully burn the resin. Our burnout schedule is ramp to 300F
hold 1 hour, ramp to 600F hold one hour, ramp to 1500F hold for
three hours, ramp down one hour to 1100F or your desired casting
temperature. You can actually do a three hour or so burnout if your
in a great rush, but in general we recommend the above. The lower
temperatures are very important and should not be rushed Casting we
cast with a centrifugal casting machine or for platinum the
traditional upright machine.

We cast many ounces of Gold and Platinum every week for large
accounts and have a very high success rate, and failure is usually
based on traditional casting problems such as sprueing, too cold
metal, Flask temperature, etc not the resin.

The models can be molded, but unless you need a mold there is really
no need to make one. The casting of resins is a more scientific
approach, but easily achievable.

This has been very brief, but gets the process pointed in the right
direction. Again the right investment and the proper high heat
burnout with air itroduced into the kiln are the primary factors in
casting resins.

Contact us with any questions.

Thomas Cavagnaro, G.G.
Cadsmithing, LLC, A Service Bureau
CAD-CAM, Casting in Gold and Platinum for the Trade
480 632 1595
Fax 480 632 1598
cadsmithing.com

10 
Now, the best solution to dealing with the near-ubiquitous ash is
to blow it out of the hot investment with an air gun, then return
the investment to the furnace for a minute or three to assure an
even re-distribution of heat before casting. I know what you're
thinking, but there has been no damage to the investment after
doing this many thousands of times. Sounds crazy, but it works.

Re Wayne’s comment above. The problem with blowing out the mold - or
any other closed cavity is that - the the offending material can’t
really get out very easily because the flow of air is going in. I use
a vacuum cleaner, hose clamped in an upright position with a heavy
piece of wide meshed screen over the end, on which I hold the mouth
of the hot mold just prior to placing in the casting machine. This
has proven immensely effective in getting out any loose investment
particles or kiln insulation bits which have fallen in during
burnout.

Do not try this without the “buffering” screen. Putting the hose end
directly against the mold will actually suck out any thin investment
formations and even the core section of a ring. Believe me. I know.

Les Brown
L.F.Brown Goldwork

11 
What kind of wax is used for "grown models"? Does the wizard wax
(orange stuff) have a high ash content ? Please let us know about
this wax and what can possibly be used as a substitute.

I’ve now had five months experience with the ProtoWizard orange wax
and, bar none, it is the finest available. It burns out as nicely as
the Ferris/Matt green, purple, blue or any regular injection wax and
at the same temperature/kiln cycles. It carves and machines far
better than Ferris/Matt and there is no distortion of the shape as
areas thin; there are no bubbles inside the block/rod (big problem
with Wolfe wax and, to a lesser extent, with Ferris); ProtoWizard wax
is less brittle than the green waxes so breakage is actually a thing
of the past; and finally, of huge importance to me, you can see what
you’re doing. The green, blue, and purple waxes are so dark in value
I’ve always had a hard time really seeing what I’m doing. It also
seems to be less offputting to customers than the green. It’s not
exactly “metal gold” but more natural (and easier to see, did I
mention that) than the Ferris/Matt products.

And no, I don’t have any financial interests or kickback
arrangements with the makers of ProtoWizard software and waxes.

Les Brown
L.F.Brown Goldwork

12

Richard

First it is important to differentiate the materials. The term
“resin” does little to define what type of material is being cast.
There are two basic types of materials being used for 3D printing
(RP) by jewelers, photopolymers and thermal plastics.

The documented history of ALL photopolymers is that they are
hygroscopic, meaning that they will expand when exposed to water.
Photopolymers are also subject to thermal expansion at higher
temperatures. When you invest these patterns, the warm and wet
environment in the flask will cause them to expand. As the investment
dries, the pattern gives up the moisture and contracts away from the
boundary between the pattern and the investment. This can cause small
or sometimes large surface defects in the investment surface before
the burnout phase. These defects are greatly dependant on the
geometry, volume, and surface area of the pattern. The larger the
design, the less likely you will achieve success. In the second phase
of burnout, which is where the investment companies have focused
their effort, the pattern expands again when subjected to heat and
may damage the boundary between pattern and investment as well. To
the degree one can control the time that a pattern is exposed to
water in phase one and the strength of the investment in phase two,
you will achieve a level of success. I know of some companies using
small flasks that are doing OK with photopolymers but, I know of none
who are getting results “just like wax” every time. The best solution
has been to cast several patterns and to cherry pick the best result
or to be satisfied with a less than pristine surface finish

The thermal plastics will dissolve in water and even faster in
alcohol or acetone. They are also much more fragile but, they will
hold up very well during the investment phase. They do not absorb
water or expand. In the burnout phase, the thermal plastics behave
exactly like wax. There is no expansion and thus a regular investment
and burnout cycle will work just fine. The only caution with these
materials is to keep them away from de-bubbler solutions that contain
alcohol and not to over vacuum the flask.

I did a scientific study on this subject with Teresa Frye at Techform
Casting not too long ago for the Santa Fe Symposium which is
available on the MJSA site and goes into more detail.
http://www.mjsajournal.org/features/0508

If you need more feel free to contact me off-line… I
have been on the bleeding edge of this subject for quite some time
and will be happy to provide some guidance

Steven Adler
A3DM

13

Richard,

I am using a solidscape machine to produce my waxes. This is what the
wax looks like:

http://www.3stepdesign.com/index/portfolio-small/3.jpg

I can’t remember the last time I had a problem with casting. The wax
in most cases is not the problem. My advice to you is to look for a
caster who has experience casting these waxes.

If you need a referral let me know

Shahar