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Centrifugal casting without vacuuming investment


#1

Greetings, Orchidians

I am in the process of setting up a centrifugal casting studio for
my shop. I’m going over my equipment list and I am struggling with
the idea of a vacuum table. I haven’t ever gone through the casting
process without one, but with a vibrating table and those liquid
films that you can spray over the wax, is it feasible to do without
it and still get consistent casts? At ~$700, it is a large chunk of
my budget for this project, but I am willing to spend it if it makes
that significant of a difference in the final product. Are there
cheaper alternatives that I’m missing? (Other than building my own- I
don’t think I have the engineering know how to put one together.)
I’ll be casting as little as several times a month to every few days,
depending on the season. Thanks for your advice!

VM


#2

Vashii- I know 700 bucks is a lot of money. However, consider the
amount of time that you will have to spend cleaning up castings with
air bubbles on them. Don’t forget that your bench time is worth
money.

When I was a metals student we didn’t have a vacuum and I remember
spending endless hours knocking off cast in place bubbles of metal.

You can make your own vacuum table. It’s not that hard. Really and
so worth it. You can also find them used. For the record I also do
prefer vacuum casting to centrifugal casting. Same machine, we just
swap out the rubber investing pad for a heat proof casting pad. Less
dangerous, no flinging metal.

Have fun and make lots of jewelry.

Jo Haemer
timothywgreen.com


#3

Vashi,

I plan on building my own.

Not absolutely positive it will work, bat at this stage, I cannot
think of why it won’t. And I am looking at less than $200. That’s
including $150 forthe pump. Won’t be as pretty as the commercial
one, but it will be smallerin size, yet with the same capacity.

I am going to Start in a about a week or so, if it works, I can post
my design. Which probably isn’t mine any way, just can’t remember
where I would gave seen it.


#4

VM-

I can only answer your question by saying it is my preference every
single time to achieve the highest standards in making jewelry. I
challenge myself to strive for the best methods at every step along
the way.

For me, when I carve an intricate, very difficult wax, the last
thing in the world I would want to see when casting would be random
air bubbles that get turned into metal spheres that are stuch or
fused in impossible to clean out areas ofa complicated design, and
effort.

Why bother skimping out on the right tool that you’ll need a few
hundred times a yeare

I’m sure there’s other benefits by using a vacuum table for the
plaster too. But possibly having air bubbles turn into design
damage(s) alone is enough to make the choice and get the best
equipment for best consistent results.

But what do I know, I’ve only hnads-on cast tens of thousands of
times.

I’m sure casting can be done in many other ways. So it is up to you
in the end to decide on how much you want to screw with casting
defects and the extra time(s) it will take you to try and salvage
the final product(s)

Imho, if you’re casting that often, one would imagine you will be
making enough profits in short order, to pay for a vacuum pump, and
table with bell. If you’re in a major city, maybe try finding a used
one.

hth
Marko


#5

I have done this every way you can think of. over the years.
Vacuumed the investment with deiozined water is the best way to go
to eliminate problems. If you can figure out how to mix the
investment under a vacuumed you will eliminate all bubbles on the
wax and have much less clean up time in the end. I built one systems
years ago. But in setting up my new shop put out the money for a
commercial unit $12,000.00 because what I had learned from my
previous experiment. Saved me much more in clean up time then the
cost of doing it right. Castings turned out better then my
competition so I made more money in the end…


#6

If you are at sea level you can use an aspirator (Google vacuum
aspirator) to vacuum small flasks or you can get an automobile air
conditioning pump from a salvage yard and use a 110 volt motor with
a pulley and a fan belt. When you run it, thetube that is sucking air
is connected to a bell jar. It will be strong enough to vacuum
several flasks at once.


#7

What is the pressure necessary to degass investments on average? I
will be buying a chamber to degass silicones and was wondering if
the chambers would work on investment as well. the chambers withstand
80 psi

Teri


#8

In our shop we do 3-6 castings per month or so, small flasks with
one or 2 pieces per flask. We have only the vibrating table for the
investment and a smallish centrifugal caster. Our castings came out
just fine. I believe that if you are only doing small flasks and not
production stuff this is the best way to go.

charlie


#9

I have been casting for years without a vacuum set up and there is no
problem you can use a vibrator or in the old day we would drum on the
table and flask to get the bubbles moving. But the real trick is to
use debubblizer and dip or spray a thin coat of thinned investment
over the waxes and let sit fora minute or two to set up before
pouring the investment down the side of the crucible.

Have fun no fancy tools in my shop, I love old school.

Lauren


#10

Not really.

I tried with sprays, careful pouring, special investments, and still
had many problems without vacuum. These were mostly unwanted
bubbles, but many of them sometimes, and also, bad fills in negative
areas. So I bought used, non-jeweler equipment. Look for a vacuum
dryer jar-these go used for about $75-125 and some are quite large,
and a vacuum pump from the air conditioning trade. My pump was $60,
my jar $75. I needed to buy pump oil, and that was $18. I now get
perfect, bubble free and totally filled casts. Considering the price
of silver and gold, I think it’s worth spending the extra hundred or
twoto get yourself set up this way. Also, it turns out that if you
ever use liquid room temperature molding compounds, it really works a
lot better if you can vacuum it. Again, for the same reasons.

Joris


#11

Its not a major project to build one with any reversible hose input
vacuum machine (like a shop vac), a good rubber mat and a cloche
/bell jar and a few other parts. Other than having to spend A LOT of
time cleaning the castings using investment there are many direct
casting methods that don’t require vacuum investment process- like
sand, delft clay, cuttlefish bone and my favourite- the sling
casting method. There is also steam casting. Simple if you make the
handle correctly (Tim McCreight’s “Complete Metalsmith” has a good
basic instruction for making the handle. There is also a process
called shell casting, again, a non-vacuumed process but getting the
investment or slurry you use even and without bubbles is important,
this is an ancient process used from Africa to the Western
Hemisphere and Europe pre-12th cent. so it’s been done for many years
in many cultures. It’s a one time mould and can be dried in an oven,
the sun or a closed car in summer with slight crack in a window so no
water vapours accumulate! having your model coated with an agent to
prevent bubbles on the surface helps with the home-made vacuum table
method- or any wax or organic model too. so there are alternatives to
a 700 dollar outlay, including a lapidary or mineralogical society in
your area that may have equipment for member’s use. Check the AFMS
homepage for org.'s in your locale if in the US, if not there are
some international lists available on-line of related organisations.
rer


#12

Historically, before we had vacuum pumps, casters would carefully
paint a few layers of the investment material onto the piece. As long
as the layers next to the piece don’t have bubbles, you should be
good to go (most of the time). J


#13

When I started making jewelry in the mid 70’s, bubbles adhering cast
models were more of a common occurrence. Sometime after that,
investment manufactures added a “wetting agent” to the investment
and that really reduced the issue of bubbles. Like so many other
things, I don’t know how it works, but it has nearly eliminated the
problem. You do need to buy or make a simple vacuum table, it’s
really a necessity when investing. If you’re pinching pennies and
want to vacuum cast without buying the more expensive two sided
set-up, I did see that Stuller is selling an aluminum box that sits
on top of your investment vacuum table rubber and you can use that
to cast (see youtube link below). Personally, I prefer to spin my
castings. For me it’s close to a spiritual thing, like a Japanese
tea ceremony, always the same sequence, always beautiful results.

Mark


#14

Teri, I was under the impression that silicone prefers pressure, not
vacuum?

Christopher Lund
Neurascenic.


#15

The late Brent Kington used to do a lot of cast jewelry/toys that he
would invest by mixing a small amount of investment that he would
apply to the wax model with a paint brush, then fill the flask with
a second mix of investment. He would visually look for bubbles as he
was applying the first coat and break them with the brush or wipe
them away from the surface of the wax. The only bubbles that are
going to cause trouble are the ones right on the surface of the
model.

I wouldn’t want to do production casting that way, but for little
one-off sculptures, it worked for him.


#16

Hi

my vacuum pump is from the air conditioning industry. It connects to
a steel box with a detachable perspex lid.

I have a rubber seal on the lid.

Also, it turns out that if you ever use liquid room temperature
molding compounds, it really works a lot better if you can vacuum it.

sure does and add silicon oil to thin it. Paint it on the master and
then prick any bubbles. Slowly fill the mould from one corner.

I cure my in a warm oven. Really gives the wife the sh*ts, till she
gets a piece of jewellery LOL.

Richard


#17
Historically, before we had vacuum pumps, casters would carefully
paint a few layers of the investment material onto the piece. As
long as the layers next to the piece don't have bubbles, you should
be good to go (most of the time) 

If one was to use this approach you would have to wait until the
painted layers completely dry before continuing to invest, the
expansion and contraction of investment can create problems and
affect the wax pattern.

If you poured a flask and did not fill it and try to mix more and
addto the top, the top layer will pop off after heating in the kiln.
However, if you donot mix enough to fill a flask to the correct level
above the waxes, you can grab a piece of cured investment and push it
into the flask to raise the liquid investment above the waxes without
consequence (as long as you don’t hit a wax pattern).

Richard Hart G. G.
Denver, Co.