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Vacuum casting


#1

Hi Jason, You might try changing the vac oil in your unit. You
might squeek out another .5". The model you have probably has a
3cfm pump and 27.5 inches of merc is about what you can expect
depending on the barometric presure of a given day. Yes that works
OK for small flasks. Find a local jewelers school and post it
there. Hope that helps. J.A.


#2
      pulled 27.5 pounds the guage goes up to 30 <pounds and I
cant remember if that is enough pressure to cast with or if my
machine needs some repair.

Jason -27.5 pounds should work fine.I fouled-up this week end;left
my bell jar inlet untight but still made a perfect cast with only
15 pounds of vac. I thought it was ruined for sure. I suspect with
good spruing you could trust 25 consistantly. I’m sure your local
lapidary club would accept a donation of your old ,weak machine.
regards,Gary


#3

I’ve meant to ask Dan Grandi …awhile back in a post you made a
statement I thought someone would pick up on…well no one did so
I will bite …I don’t save the posts but I remember the
statement …paraphrased

centrifical casting ..don't see any reason for it..only do
vacuum casting 

Dan , would you please elaborate on your reasons…I would be
interested in why you feel this way ?

Terry Parresol


#4

Terri, if Dan doesn’t take your question, I will. I don’t
remember seeing that post, but I totally agree with him. I
bought a vacuum unit, about twenty years ago, and have done
virtually no centrifugal work since. The vacuum unit does not
need to be balanced, wound and can’t slip and destroy knuckles!
It also won’t spew forth if you overestimate the amount of metal
needed. I can’t think of anything that I could do with
centrifugal that I can’t do with vacuum. Hope that helps, Curtis


#5

Terry, I’m not Dan, but I’ll give you MY two cents, for what
it’s worth.

I greatly prefer centrifugal casting. I find my castings are
better quality, and finer grained than if cast with vacuum. A
firm I’ve worked for feels the opposite, with the caster saying
he’s never had much luck with a centrifuge, and they are happy
with the results they get with their vacuum castings. Usually,
they are casting small flasks with only a few items per flask.

Like I said, they are happy. But I’M one of the poor saps who
had to clean up those damn castings, and I’m here to tell you
they are more porous, with larger grain size, poorer surface
finish, and just as many problems with investement breakout or
finning as anything I ever saw with centrifugal casting.

On the other hand, the firm I worked for prior to that was
actually a trade casting firm. They’d grown, over the years, and
moved from torch melting and casting with a kerr centrifuge to
induction melting with a commercial grade vacuum machine, and the
castings produced by that machine were beautiful, and were done
at lower cost and less effort than with a centrifuge, due to the
large flask size allowed. But proper use of such a machine to
get those results requires careful attention to flask
temperatures, sprue and tree design, and the other variables
involved in casting. If you’re used to investing just by
eyeballing the mix ratio, and heating till it looks “hot
enough”, etc, you’re in for some dissappointing castings. That’s
true no matter what technology you use, but it seems to me that
vacuum casting seems especially prone to needing to be done right
if the resulting metal is to be of high quality.

The key here, I think, is the flask size. Vacuum casting relies
only on the weight of the metal column in the sprue and tree to
supply the force needed to fill the mold and keep the metal
dense. With small flasks, you have less of this, and also have
less potential temperature gradiant from the center to the
outside of the flask, so must often cast at hotter flask
temperatures to get complete fills. That hotter flask translates
to larger, coarser grain size, as well as poorer surface finish,
and less pressure on the metal also gives you less density/more
porosity.

Centrifugal casting puts more stress on the mold, so you must
pay careful attention to how you sprue, and your investment mix
and procedure, to avoid breakouts and cracking of the mold. And
the metal is being slammed into the mold faster, which while good
for filling the mold, also increases turbulence and certain types
of porosity. Again, careful and proper spruing is essential. But
the bottom line, for me, is that since I usually am casting
smaller amounts (Almost always less than two ounces of gold, and
often more like one ounce, at a time) into smaller flasks, I feel
that the ability to use cooler flask temperatures and still get
completely filled, dense castings, gives me on the whole, a
better result.

Peter Rowe


#6

Hi Terry and all …To answer your question as to why i prefer
vaccumm casting over Centrifuge. Having Started centrifugal
casting in 1968 all the way through 1978doing 24k,18k
gold,22k,14k,10k,(for europe 8k)in white, yellow,red golds and
sterling silver as well.Platinum was done on a different
machine. All the machines i had used up till that point were
spring wound , also motorized, induction(high frequency)
melted,Resistance melted and torch melted. In 1978, i was
introduced to the concept of vacuum casting.Both, for very small
scale (couple pieces here and there) all the way through high
volumes of up to 15,000 pcs /day in some of the bigger factories
.

In the 1980’s I concentrated on designing and building machines
for the jewelry trade as well as Consulting, marketing and sales
of jewelry machinery for a few different companies. During this
time i had the ability to visitLarge and small manufacturers all
over the world and got a chance to formulate my own personal
opinions through large amounts of observation and testing. The
first thing that i could say about lost wax casting is this.The
quality of your castings is 1st and foremost directly due to the
experience of the person doing the casting. Any kind of equipment
or lack thereof can be made to work, although some methods are
EASIER than others. Certain Alloys that can be used in this field
work best as Centifugally cast and this was true of many alloys
in the 1960’s through the 70’s. In the 1980-90’s many new alloys
for golds and silver have been Developed by various individuals
and metal suppliers that far exceed the metals of previous years.
Most of these alloys work extremely well when vaccuum cast.It is
important when you buy your metals to mention to your supplier
what kind of casting you do so they can suggest what would be
optimum. You will notice that most of your Jewelry supply
companies have been selling vaccuum casting equipment and
advertising Vaccuum equipment much more so than Centrifugal
casting machines. Here are the reasons. 1) A simple vacuum caster
is very inexpensive to buy and learn to operate. A high tech
Vaccuum caster ( for Large Volume)has very few moving parts and
, in general , requires very little maintenance over the years.
All vaccuum casting systems can use small to large flasks… (I
use 2"x2" Dia. x Height flasks to 6" Dia to 8" height flasks all
on the same $500. vaccuum casting machine). There is no need to
adjust the cradle,balance the assembly and change the swingarms…
as you have to do with a centrifuge… because there are no such
devices on a Vaccuum caster. 2) It is far easier to train any
person to use a vaccumm caster than a centrifuge and far less
Dangerous during the training period.

3)The castings surfaces on a vaccuum machine come out smoother.
It is easier to learn how to get good quality castings with a
vacuum system. Usually a couple experiments at the beginning will
answer a thousand questions. 4)Being at the proper metal
temperature for casting is a critical aspect of casting. In a
torch melt system for vaccuum casting,it is easy to see the
metal melt, (if, as in my case, you use a microphone stand
modified to hold your torch, this will allow one person to
easily melt…when your metal is nearly fully melted…get your
flask out of the machine…put it on the vacuum caster… take
the torch off of the microphone stand… follow your crucible
with the torch on the metal and pour your metal through the flame
into the opening of your flask.)In this manner, it is all a one
person show .It is important not to let your flask cool down too
much before you cast . In a centrifugal sytem( torch melted) …
it is not as easy and it takes longer to accomplish and more
Dangerous.

I wish again, to express that these are my opinions and that i’m
sure that some may disagree… but just think back to that first
day or 2 of centrifugal casting … when the metal flew all over
the room … and put pin holes in your shirt… or you got the
s_ _ _ scared out of you when the swing arm was out of balance
and shaking like crazy…the flask blew out and Your Still trying
to get the gold off the one of the scews on the machine…Boy
!!! Them good ole Days sure were Fun !!! I hope this helps and
if anyone has any questions… just ask. Daniel Grandi
Http://www.racecarjewelry.com


#7

All the pros I’ve talked too and I have been vacuum casting for
5 years with never 100 success with a 15/20 item tree … so I’m
on my way to Centrifugal and won’t look back!!! . . People that
cast in the hundreds per day… suggest that Centrifugal is for
playing around… and I agree…

Tried everything possible for success… never happened(passed
tense) The big ‘V’ is ok for 4/5 waxes … that was it for me
if I want success in the 85/100 range . . anxious to get on with
’C’ casting.

Jim


#8

Hi Terry, I spent 20 years using a centrifical machine. About 3
years ago, I tried vacume casting. I kept the centrifical machine
set up in case I needed it. I haven’t. I have fogotten about the
problems I used to have with porosity, ovefill, cracked flasks
and the whole bit. I use more sprues on delicate pieces because
friends have warned me that there is less force involved. I have
had absolutely no problems with vacume casting. [I still use a verticle casting machine for platinum]. Have fun. Tom Arnold


#9

Hi,

As far as comparing vacuum and centrifugal casting, I have both,
use both and like both. I think if you are doing mostly custom
work and casting less than ten waxes at a time, you get very
comparable results with both. Because when you are casting just a
few items at a time you can sprue directly to the button, that
alone really cuts down on the misses you might have. I think if
you had two experienced casters, one using a centrifugal and the
other using a vacuum, cast a few waxes for you there would be no
noticeable difference in the results. Once you start sprueing
larger trees it is much better to vacuum cast. You have too much
metal to spin when you are doing 100+ dwt. pours. It is easier in
that case to use a hand furnace and vacuum.

I rarely have more than 8 items in a flask and almost always
spin, we have excellent results so why change. I spent my first
10 years working in a larger shop that usually had 25 to 50 items
per flask and I always used a vacuum in that case. I think people
are wrong to blow off one or the other, they both have there
place and both can produce an excellent product.

Mark P.
WI


#10

Don got me all interested in trying vacuum casting again since
he seems to have such luck with it. Well, I for one have never
been able to get a good cast with vacuum and have tried it 3-4
times now. I do all the same things I do with centrifugal, same
burnout, same investment, same flask temp (900 degrees F) and
same melt. Every time I get tiny micro porosity allover the piece
that has to be polished off, I get pieces that detail is soft
on, and last time I used non-ox alloy and got nasty porosity all
through the bulk of the piece that couldn’t be polished out.
Personally I prefer centrifugal, I’ve had better results and its
what I’ve been working on perfecting for five years now. Don says
most production casters use vacuum and I’ve heard this too. I
think which method you use, either one can be perfected but my
opinion is stick with one and master it, and of the two I think
centrifugal might be easier to master. I use a Neycraft
Spincaster which has a built in shell that spins with the
crucible and for smaller volumes of metal its an ideal machine
for me. If you use too much metal the shell catches it. I read
somewhere that vacuum casting is better for casting trees and
larger volumes of metal and my experience seems to suggest that
might be true. For me, I won’t mess with vacuum casting
again…Dave

Crystalguy Jewelry, the first art jewelry site on the net
http://www.opendoor.com/stephensdesign/crystalguy.html
Art jewelry with a mystic touch / Now accepting credit cards


#11

I have to agree with Curtis… I find that vacum casting just
makes more sense… No danger of anyhting happening like getting
burnt from flying gold, or mamed by the unit itslef while in
operation… Marc


#12

If one was to start from nothing, which would be less costly to
initiate, vacuum or centrifugal casting setups? What would
one need to set up each on a minimal basis?

Thanks,
Bob B

I’ve enjoyed the controversy and all the great replies!


#13

Hey Dave S if you are having such a hard time Vac casting…
give me a call.I did give you my number . I have taken people who
have never even Made jewelry and in 2 days got them to cast well
enough to start their own businesses… and Its DAN… Not Don
Dan Grandi


#14

Hi Terry,

Listen to Peter Rowe. I am in the dental industry and we cast
our little hearts out and other than inert gas casting(this may
also be centrifugal casting) I know of no one who casts with
vacuum in my area. I have cast in excess of 32,000 dental
restorations all centrifugally.

Regards,

Skip

Skip Meister
@Skip_Meister
N.R.A. Endowment &
Certified Instructor
in all disciplines
Certified Illinois D.N.R.
Hunter Ed, Instructor


#15

I cast up to 30 flasks a day some that have 100 parts or more
on a tree and some that are a single ring some are 5" x 8"
flasks and some are 3"x 3" flasks all of them using vacuum
casting. I get excellent results more consistently with vacuum
than with centrifuge. The centrifuge is too forceful you get
more defects from turbulence and cracked investment with the
centrifuge. The single biggest problem with vacuum casting is
poor melting practice the second biggest problem is improperly
sized flasks for the parts being cast. If you allow air to get
to the metal when melting or pouring you will have porosity
problems. If your flask is too big for the parts being cast you
will have incomplete fills and low density parts. Pay attention
to these two problem areas and you will have good castings with
a vacuum setup.

Jim


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-436-3552


#16

I have to say I like the vacuum. I cast as much as 24oz. at a
time and as low as 5dwt. thick and thin, small and so big that we
have to have one-of-akind flask made to accommodate them. I also
think it very. very important to say that it is not always the
machine. No matter which you swore by, a machine is a tool, and
if you don’t know what you are doing or the material you are
working with, you will never have good or constant results The
kind of metal, the size of the sprue,how you attach to the
base, the temperature of the metal, the temperature of the
flask, how fast you burn out, and know why for all the above.
Because one has a casting machine, doesn’t mean one knows how
to cast. We get close to 100% turnout and we still have a lot to
learn about what we are doing and why. A lot of trail and error
and once in a while a boo boo that make no sense what so ever. We
get new customers all the time running from the spin casters
and I see what they bring me. And for the most part there’s no
excuse for the quality, not if you know what you are doing.

  $.02  From Robert

#17

Peter, Thanks for the input also…over the past 15 years I too
have done mostly centrifugal casting, small stuff, one ring or
whatever at a time with less problems as the years went by ,or,
hmm, that was past tense, I mean go by…Daniel’s comment
intrigued me so I asked…did a few vacuum casts last few
weeks…new learning curve I guess cause mine wernn’t so good…
commercial waxes for the case so no problem with customers on
these few casts…

Just another process to learn…But your comment about casting
temperature with vacuum…what ? with centrifuge I let my flask
get between 800 and 1000 degrees depending upon whether I have a
heavy ring or a lighter ring or pendant or yellow or white
gold…If I read your comment correctly one should use a hotter
flask temperature for vacuum than for centrifugal…?

I could just stay with my very old old centrifuge mounted in a
old washtub but then I wouldn’t learn more…like I need to
learn more… just began on advanced parts making for high grade
watches, more advanced lathe work on watches and I was wondering
if these CAD programs could design a watch from the ground up
instead of doing it on paper…I would like to design and build a
tourbillon but probably not feasible yet on the computer.

So I’ll increase my temperature a bit on my next vacuum cast
and see what happens. And Peter what is your opinion on the
comment about different casting grain for vacuum or centrifuge ?

Terry Parresol


#18

Hi peter and all… I will disagree about your statements on
vacuum casting versus centrifuge. You apparently had a bad
experience with someone who did vacuum casting for your previous
shop…but it takes far Greater experience to cast reasonably
well with a centrifuge and it is more difficult to teach and
far more dangerous to the novice.(I have taught both processes
in factories and schools as well). As far as flask size and
Quantity… again, i must disagree with you.I do 2x2 flasks in
all sorts of metals for many designers 1 off pieces and custom
cast pieces for jewelry stores. Also , i produce about 2000
pieces /week of extremely high quality…smooth high polished
mirror finished pieces for some of my own customers . My average
Flask is 5" dia x 7" tall holding h between 30 to 150 pieces on
a single tree.Occasionaly we use flasks that are 6x8" in dia.
with as many as 300 pieces on a tree… I use standard solid
flasks and a vacuum liner that i designed called the Tyvac
vacuum liner Available from http://www.contenti.com also
available through the Guesswein co ( from Elaine). This vacum
liner is made of a special paper and burns away leaving multiple
vacum channels that greatly increases the efficiency of vacum
casting…allowing casting to be cast quite a bit cooler… at
the same time…in the investing process automatically creates
an overflow sleave that stops your investment from overflowing
the flask and making a mess in the Investing process(its also
Inexpensive to use). There have been other vacum enhancers that
also worked in the past… but this one works the best… the
paper is not affected by heat /cold or shipping . When you
mentioned that the only thing that helps the metal enter the
flask is the weight of the metal…well… the vacuum helps
quite a bit and the height you pour from as well .

I am not using a fancy machine… i have had them and used
them. i have a $500 vacum table and pump and a oxy/propane
torch. we melt 500 grams of silver in about 3 minutes ( which
is as fast as ) the $65,000 casting systems.( my biggest torch
melts are around 750 Grams) We melt in ceramic crucibles that do
not contaminate the metal and last for months before
replacement. The key ( as you mentioned ) is experience.And
experience on a vacum system is easy to learn and not very
expensive. If anyone wants to be a "seat of the Pants " caster
mixing their plaster by “feel” and Guessing at their oven flask
temperatures… it doesn’t mattter whatsystem is used… there
will be lots of failures that way ! I recomend Any kind of
digital oven controller (as i Have found that the oven that have
those analog dial s and bimetalic controllers are extremely
eratic and inacurate.) Guesswein has some good ones that are
inexpensive.

Here is a true story that is relevant. When i was selling/
designing jewelry machinery in the early 80’s a man came to me
where i was working and showed me a casting of a famous horse
that is used on a famous trophy in the horse racing field. He
told me that over the past 20 years … this horse had been
cast by nearly every large casting company between Newyork and
RI. and every year, his bench workers had to take the castings
and fill pits and holes … spending almost 1 week on the horse
just to make it perfect.He showed me at least 10 molds that were
made ( in Rubber) of the horse with all kinds of sprues/vents
and feeds . each one from a different manufacturer and each one
done completely differently.I was told that every time he went
to a different manufacturer, they told him that they could not
use the molds or the spruing techniques that the other mfg used
… so he always had to pay for new molds.He allowed these mfg
companies at least 5 tries each and settled for something less
than perfect each time. the horse casting itself weighs 9 OZ…
in 14k yellow gold. He asked me if i knew someone who could help
him out… i told him i could do it for him. I took his molds
home… shot 2 good waxes… removed all the multiple spruing
from the waxes and put one 9mm dia (3/8") sprue right on the
Horses Rear…at an angle that you could see that the metal
would all flow in one direction. Each horse was put in it’s
own flask and loaded into the oven for an overnight burnout. The
following morning… the Gentleman came to my house with the 12
1/2 oz of gold to watch the casting process. He was shocked at
seeing my small digital oven and $500 casting table with a
microphone stand to hold the torch!!! He said to me…" you
think your going to get a good casting with the pityful
equipment you have here… when the factories i have been too
have $100,000 casting machines"!!! I said to him… lets find
out. He watched me melt the gold in my ceramic crucible… pull
the flask … turn on the Vacuum and pour the metal…after 5
seconds i turned off the machine and left the flask to cool for
almost 45 minutes. I explained to him that i had a second horse
in the oven as a back up in case we needed to try a different
flask temp.I broke out the flask and water blasted the
casting… put it in my ultrasonic in a special investment
removal solution and gave the cleaned casting to him… I
NEVER saw a bigger smile on anyones face.He was extatic!!! He
called me the next day and told me that his goldsmith had not
only finished the cleanup of the horse, but had already
installed it on the trophy . Every year since 1984 till 1995…
i cast this horse for this man.( i ended up building a casting
factory and electroforming facility for him). And to this day…
i still remember that smile on his face … and the shock when
he saw that low tech equipment it was done on…

Anyhow… sorry for being so longwinded about all this…
Sincerely,
Daniel Grandi
http://www.racecarjewelry.com


#19

Bob:

Definetly centrifical casting is the least expensive to set up.
You can buy a good machine new for about $350.00, get a small
propane or actylene tank & torch and an electric kiln. Add a few
bits like flasks, crucibles & flask bases, investment & de-bubble
solution, ect. and you’re in business. Most suppiers have a
variety of casting sets already selected to various price ranges.

Best of luck;

Steve


#20

vaccum is cheaper to set up and less expensive to maintain. You
can get a combo vacuum table and immersion caster (it is
important that you have the kind that takes perforated flasks
unless you are only doing one small piece at a time) for about
$700. A centrifugal and vacuum table will exceed this. All other
costs are the same. An approx. caost for a basic set up is $2-3
grand.