Back to Ganoksin | FAQ | Contact

Shrinkage with silver


#1

When casting sterling silver, how much shrinkage is there
because of the metal hardening. If you were designing a ring
to be a size 6, what size would you make the wax?

Marshall Jones


#2

Hi Marshal, I don’t do too much with silver but I treat it the
same way as gold. I make it the same size as what I need. After
casting I’ll round it and sand finish the inside to smooth it. By
that time it’s back up to the original size I needed. If not,
it’s nothing to tap it up a quarter or so. It’s better to be a
bit smaller than to be too large. Michael B


#3

Aloha Marshall, Ring shrinkage varies due to many contributing
factors.Namely size of the piece(wax mass),mold
shrinkage(wax),thermal expansion(investment),hydroscopic
expansion(investment),setting expansion,cooling the
casting,etc.,etc.All pretty boring and unnessary precautions and
concerns,unless you are casting precision parts or teeth.I say
from experience around 1 size(or 3/4) is about average.What does
everyone else think?

Regards,
Christian Grunewald
Precision Modelmaking
Hawaii


#4

Hello Marshall, Just make your wax in a size 6. By the time you
clean up the casting, round it up on a mandrel and then polish
it, the ring will be a 6. If you are making a model from which
you expect to make a mold, then you should make your wax about
10 per cent heavier than you want the finished piece to be. The
ring size should then be a 1/4 size big on a medium weight ring
and 1/2 size lrge on a really heavy ring. Make it a 6 if the
ring model is to be very thin. I hope the piece comes out great.
Tom Arnold


#5

When casting sterling silver, how much shrinkage is there
because of the metal hardening. If you were designing a ring
to be a size 6, what size would you make the wax?

In my experience there seems to be around 4.8 to 5% shrinkage

I hope this helps.

Regards,

Kerry
Kerry McCandlish Jewellery - Celtic and Scottish styles
Commission/Custom Work undertaken…http://www.bennie.demon.co.uk
Katunayake, Creagorry, Isle of Benbecula, HS7 5PG SCOTLAND
Tel: +44 1870-602-677 Fax: +44 1870-602-956 Mobile: +44 850-059-162


#6

When casting sterling silver, how much shrinkage is there
because of the metal hardening. If you were designing a ring
to be a size 6, what size would you make the wax?

I usually make the wax slightly smaller. Very easy to hammer a
ring up the mandrel a little. Also helps to compact the metal.
I’m much more concerned with making the ring heavy(read thick)
enough, as finishing can can possibly thin the ring out too
much.

Bruce D. Holmgrain
e-mail: @Bruce_Holmgrain


phone:: 703-593-4652


#7
  When casting sterling silver, how much shrinkage is there 
because of  the metal hardening.  If you were designing    a
ring to be a size 6, what size would you make the wax? 

The actual shrinkage percent will vary with the nature of the
wax model, metal thicknesses, flask temps, and similar variable.
Sometimes, there’s next to none, if the flask is hot enough so
thermal expansion of the flask matches the metal shrinkage on
solidification. Some dental investments are designed especially
to give that compensation. But your answer to sizes is simple.
Make the wax the size you wish the ring to finish out at. The
slight shrinkage in size (usually less than a quarter size, in my
experience) is just about right to allow you to clean up the
casting and polish it, inside of the shank included. After that
sanding/filing/polishing/rounding out, etc, it should end up the
size you need. You’ll generally loose more in polishing and clean
up than you did to shrinkage, so allow enough, especially in
thickness of the model, for that. Around .2 mm extra thickness
at least, usually. Shrinkage is more of a problem when rubber
molding and injecting models. The rubber mold shrinks a bit,
the waxes shrink (and distort and gain mold marks) in the rubber
mold, and then you add metal shrinkage in casting, and NOW you’ve
got a significant amount of shrinkage over the original piece the
mold was made from.

Hope this helps.

Peter Rowe


#8
When casting sterling silver, how much shrinkage is
there  because of  the metal hardening.  If you were
designing  a  ring to be a size 6, what size would you
make the wax? 
    The actual shrinkage percent will vary with the nature of
the wax model, metal thicknesses, flask temps, and similar
variable. 

To this fine advice I’d add this. If you are making a ring with
a bezel from a METAL MASTER (not all rings originate from wax)
then the size of the master bezel can be critical. I made a
series of sings with 10mm pushover bezels and on my first attempt
I allowed too much for shrinkage. The resultant bezels were too
big. I needed to make it only 3% larger, IIRC. other parts of the
same ring shrank at different rates, depending on the shape, I
guessed.

Brian
B r i a n =A0 A d a m J e w e l l e r y E y e w e a r =A0
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz


#9
 I say from experience around 1 size(or 3/4) is about average.
What does everyone else think? 

I find 1/4 size for yellow gold and sterling is plenty. Even
closer to finish size for white gold. You must be removing a lot
of metal in finishing, or spending time sizing back out (?). Mike


#10
 To this fine advice I'd add this. If you are making a ring
with a bezel from a METAL MASTER (not all rings originate from
wax) then the size of the master bezel can be critical. I made
a series of sings with 10mm pushover bezels and on my first
attempt I allowed too much for shrinkage. The resultant bezels
were too big. I needed to make it only 3% larger, IIRC. other
parts of the same ring shrank at different rates, depending on
the shape, I guessed. 

Right you are Brian. The key here is that now we’re talking
about a rubber mold and injected waxes. For this, I’d suggest
that people each run their own tests. Take a model, any model,
mold it using your standard techniques, inject it and cast it,
again as you’d normally do. Now measure and record the
differences. The reason that this is a good idea is that several
of these processes can have different degrees of shrinkage
depending on small differences in technique. Exact temp settings
on the vulcanizer, for example can radically alter rubber
shrinkage, as can different brands of rubber. Precise wax
injection temperature also has an effect to alter the shrinkage
percentages. so does casting temp, both the flask and the metal.
All in all, while Brian’s 3% figure is a good starting point,
I’ve seen it go, even with a rubber mold, from almost 0 up to
almost 8%, depending on type of rubber, type of wax, type of
metal being cast, etc. A key point to remember here is that
casting, to be consistant and reliable, needs to be done as a
precision operation. Many of us learned to cast as a seat of the
pants (Gee, that looks about right…) sort of thing. This may
work surprisingly well much of the time. But if you need
results to be really reliable and consistant, then you need a
much tighter handle on the process. Exact knowledge and records
of temperatures and times and the like used in various stages of
the process will not only allow you to predict the results much
more completely, but also make it much easier for you to isolate
and solve problems when they occur.

Hope this helps.

Peter Rowe


#11

Regarding or should I say adding to Peter R.'s two cents, he’s
right , most of us do learn by the seat of our pants when it comes
to casting. I’ve personally been casting since high school 76 –
79, and then profesionally since 85, and learned to keep very
precise records of ALL variables. All meaning anything that can
affect your final results, which can be everything from the
humidity to the day of the week, well you know what I mean.
Keeping a written record to go and look back on and following a
certain procedure can make all the differance in knowing why
something does or doesn’t do what we’d all like it to do,ie; give
us a perfect casting EVERY time. I was once told bye Eddie Bell,
of Rio Grand that the reason they call investment, investment, is
because of all the time and $$$ INVESTED in comming up with a
formula for the right stuff to cast metals in and have them come
out , period!! You think you got it down and something comes up
you never thought of!! But try keeping some kind of record and
you’ll find that you can track down certain problems most of the
time!! Good luck! Matt the Catt


#12

Aloha Mike, I don’t make any shanks less than 1.8 to 2.0 mm
(finished and not much needed at that).Mass does make a
difference on over all shrinkage,as does
quenching(silver),casting temp and the other many
factors(mentioned in the previous reply).I as a rule, make my
waxes 1/2 size larger than the desired size.Work hardening a
piece through hammering it up on mandrel,is not the question(and
not desirable,for my purposes).From a master to a wax,say in
castaldo gold label,the shrinkage is approx. 6%-as much as
10%.Just the investment(R&R,for example) may cause 1 1/2 to 3%
shrinkage.So,say you make a band by hand,the material required
to make the band of said size is 58mm.Subtract 3%,that is
1.74mm.One size is approximately 2.25mm(.5625mm is 1/4
size,approx.).Do the math.Also you may want to see if all your
mandrels,read the same(most times,they don’t).Just my opinion.
Regards, Christian Grunewald Precision Modelmaking Hawaii


#13

Isn’t the shrinkage due to; Latex molding, Casting investment
brand, wax brands more so than the shrinkage of the silver or
gold… understand from dental cap technicians(not sure of their
professional name) that they use completely different investment,
and wax than we do which provide NO shrinkage… Also, recent
descussion with my dentist suggest the same… The wax he uses (as
he says), “Has memory”… that is it holds the shape or returns to
the shape after temp. in applied … therefore I assume that the
shrinkage from gold and silver is very, very slight… Tried
his wax and receipted almost no shrinkage… Jim


#14

Jim, sounds logical. What was the brand of the wax, or the name
of the mfg.? Curtis


#15

Jim: As a Dentist in my first life I taught at the Dental
school and the Dental students were instructed in the art of
casting. This is no longer the case, they now write a presciption
to the dental lab technician. The wax used then and now is no
different from that which is used by jewelers. Usually it was
Kerr’s blue wax similar to wax currently used. Shrinkage was the
same. The gold alloys used did shrink a certain % as all metals
do, when going from a molten stage to a solid stage. We would
have to compensate for this inherent shrinkage in order to obtain
the accuracy demanded of our disipline, by the way we mixed our
investment (water to powder ratio) and also to allow the
expansion of the investment a certain % we would line the
investment ring with a layer of asbestos thereby permitting the
cavity in the investment to enlarge and help in compensating for
gold shrinkage when casting There was and is on magic material.
Hope this helps, JZD


#16

Hi Jim,

I’m a dental tech. I don’t think that the wax matters much at
all. I have used dental waxes(much greater carvability but not
as forgiving(tough) as say Mat Wax. Dental waxes are not able
to be carved with burrs,) and Mat Wax with dental investments
and the results are superb. I have even mixed those waxes along
with a red casting wax used by CNC machinists for machining
parts to be cast with the same great results. In Dentistry, a
stone die (exact duplicate of a prepared [ground] tooth to be
crowned) is what we wax to. The wax-up is going to be cast in
gold (usually) and is the replacement of the ground away tooth
structure. The final casting must not only fit the die but
must also fit the model of the mouth in relation to the
adjacent existing dentition AND exactly fit the opposing
dentition. To demonstrate the degree of accuracy we need, think
of the last time you ate a Strawberry or Raspberry jam sandwich
and got a seed stuck in your teeth. It felt like a house brick
in there didn’t it? We draw a red pencil line to show where the
prepared and existing tooth structures meet and then the casting
should cover 1/2 the red pencil line. From sprueing to casting
takes us less than 3 hrs., a little longer if we are casting a 2
1/2" diameter casting ring. The only thing dental waxes do is
keep their thinnest edges from curling at room temperature. If
you get up into the 80’s (degrees F)in the room their edges will
curl and the whole wax-up may deform. I hope this helps.

Regards,

Skip

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