Metal begins to cool; distances between atoms start shrinking and therefore the metal itself occupies less space when it is cold, than when it was hot.
AGAIN, your explanation refutes your whole argument! Now you say
that the shrinkage is due to lack of amount of metal??? Maybe I
missed something here but that has NOTHING to do with a hole getting
large from heat, instead it’s the amount of metal pulling the hole
larger?? 2 different situations
These pins are pulled out very easily with small pliers and sometimes with bare fingers. If the holes after casting were getting smaller, it would be impossible to remove these pins
It would depend on the relative expansion rates, don’t you think?
Assuming the statement is correct.
This is true of course, but that is because while the inside of the ring is getting larger, the ring itself is getting smaller due to shrinkage....
I don’t want to rain on your parade but you are promulgating a
series of old wives tales. (apologies to all old wives) I know that
you are a well trained and accomplished craftsman, but your
explanations are often wrong.
We have been thu the ring expansion theory. I have cast CZ’s in
bronze, silver and glass. I did it before I found others did the
same.
I accepted that a fast heat up was inevitable and did as slow a cool
down as reasonable. I felt that I could probably easily determine if
a failure occurred on heat up or cool down- overnight.
I never had a failure with my procedure although I was prepared to
accept them. some have claimed fusion in cast glass or glass enamel.
I dispute this and claim that it is all mechanical.
That is another story… I did run one test on cast of a CZ in clear
flat glass with my "normal " annealing procedure.
(I would like to know the cool down method rate where stone
failures occurred.) I never quenched any.
I examined the result with crossed Polaroid’s and saw what I
expected --a ring of stress lines in the glass surrounding the stone.
I didn’t see stress in the stone ?? So far this piece hasn’t failed.
I didn’t do more with this.
I also have investment cast bronze sculpture in ceramic shell and
plaster based investment with a core held in place with matching
alloy bronze pins. You observation that the pins remain free is
confirmed, but your explanation is incorrect.
The pins are oxidized during burnout and the surface is too dirty to
fuse in the casting. I could discuss this further but this explains
your observation.
Another area to explore is shrink mounting a faceted stone by
inserting a chilled stone into a heated machined setting. I haven’t
done any calculations on the clearances or temperature differentials
that would be required.
jesse
Have you ever done any cast-in-place work? I've seen CZ's shatter after casting from the pressure of the [contracting] hole. They cooled down and divested just fine. They blew up minutes to hours later, long after they'd hit room temp. Just sitting around waiting for the tree to get trimmed. The wrong little shock, and 'snap!'. Off they went.
Right observations, wrong conclusions. CZ(s) are not temperature
stable. Some better than others ( depends on manufacture ) but in
general CZ(s) should not be subjected to high temperature. Casting
stresses are created by many factors.
What is remarkable to me that while having explain this to so many,
I am wondering, “Am I the only guy who ever did models in silver, who
is still alive, and all the rest of modelmakers are dead” ?
You see, this is not a great mystery and should not be such a
revelation. The fact that holes after casting are large, is very
basic and mandatory adjustment that any modelmaker makes.
Leonid Surpin
Dave,
Invisible setting isn't impossible or even all that difficult if you can successfully channel set baguettes. It just requires extreme precision and attention to detail at every step to be done well.
I disagree, channel setting baguettes, even tapered ones, is not all
that fussy. Accuracy is required but it isn’t that hard. (I’m mainly
a self tought setter, when as a pretty good goldsmith I was offered
the choice between setting my own work or un-employment, it was an
easy choice ; they could only fire me once 
But the invisible stuff repairs sends me running and screaming. Life
is too short to mess with other jewellers disasters and short cuts on
a really bad technique. Even if you way over charge it will still
come back and bite you, better to be remembered as a coward than a
failed jeweller.
jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand
Maybe I missed something here but that has NOTHING to do with a hole getting large from heat, instead it's the amount of metal pulling the hole larger?? 2 different situations
I have never said that holes getting larger from heat. I said that
holes will be larger after casting. The context is important here and
the context is casting with stones in place. And the reason that
stones, which are cast in place are easily lost is that because
holes, which are formed by liquid metal and corresponding to stone
sizes while hot, will be larger than stones upon cooling.
Leonid Surpin
It would depend on the relative expansion rates, don't you think? Assuming the statement is correct.
Sure, casting can be influenced by many factors, but in general the
principal holds.
Leonid Surpin
I also have investment cast bronze sculpture in ceramic shell and plaster based investment with a core held in place with matching alloy bronze pins. You observation that the pins remain free is confirmed, but your explanation is incorrect. > The pins are oxidized during burnout and the surface is too dirty to fuse in the casting. I could discuss this further but this explains your observation.
We are not talking about fusing. If holes were shrinking, the pins
would be trapped and that is not the case. I am not sure why are you
using bronze pins, but if you like it…
As far as explanation, let me try another approach. Everybody one
time or another have had a cup of coffee with a slice of coffee cake
in the shape of a ring. Such cakes are baked in round forms with
hollow centers, to form a ring. Do you realize that if holes after
cooling were getting smaller, there would be no coffee cakes in this
universe, because these cakes would be impossible to separate from
their forms.
So as they say, the proof is in the pudding, which, in this case, is
a coffee cake.
Leonid Surpin
All the arguments are practical in nature. I’m curious if anyone
knows why the hole expands when heated. It would seem logical to me
that it would shrink when heated and expand when cooled. When you
heat metal it expands in ALL directions. A solid piece only has one
direction available and that is out. With a hole in the piece, that
would seem to be an avenue available for the heated metal to expand
into. Does anyone no why it doesn’t happen that way? Just curious
after reading all the comments.
My guess would be that to expand into the hole the metal surrounding
the hole would have to compress to expand toward a smaller diameter
area. That’s just a guess on my part though.
Jim, where are you?
What is remarkable to me that while having explain this to so many, I am wondering, "Am I the only guy who ever did models in silver, who is still alive, and all the rest of modelmakers are dead" ?
You see, this is not a great mystery and should not be such a revelation. The fact that holes after casting are large, is very basic and mandatory adjustment that any modelmaker makes.
Very strange observations indeed, Leonid. You see, I also have made
models in silver for many years, both as hand made models, and more
recently, as CAD/CAM models made from cast CAD/CAM waxes, and molds
then made from the silver casting, or the silver hand made model.
Everything I’ve ever noted is that holes, and spacing between them,
and other measurements, are all smaller. Casting shrink. Exceptions
are occasionally in platinum, or with certain high expansion
investments, where the thermal expansion of the mold from burn out,
exceeds the shrinkage of the metal upon cooling. But that isn’t metal
expanding, or holes becoming larger. That, in essence, is casting
into an enlarged (holes included) mold.
In another post, talking about ring sizes being smaller after
casting, you quite clearly explained exactly what happens, that the
metal shrinks upon cooling, and that the overall shrinkage of the
whole piece overcomes the slight enlarging of the hole from metal
shrinking away from the hole. You are correct that metal next to the
hole shrinks, pulling away from that edge of the hole. But as with
rings, the overall shrinkage of the whole piece is greater, and the
hole still does become smaller.
Effects that can mask this effect:
Oxidation of the casting which gets pickled off and results in
slightly less metal at the surface. That can slightly increase a hole
size. Doubtful that it would still be enough to make it larger than
the hole in the wax or model, but not impossible, depending on the
metal. The same with rough cast surfaces, from burnout problems, or
metal/mold reactions.
And then there is what happens in the other example you gave, that
of hollow cored lost wax castings. That’s actually an interesting
case, with a more complex explanation. You are correct that in such
work, the core pins often are loose in the cooled casting. But the
reason is not simply enlarged holes from metal shrinkage. Rather,
it’s a combination of factors. The main one is that the rate of
thermal expansion of most casting investments, including sculptural
investments or sand mold products, is less than the thermal
expansion rate of the metals. Even if the mold is hot, the core
shrinks less than the metal upon cooling, and the trapped core exerts
some pressure on the solidifying and cooling metal, literally
stretching it at the same time as it’s trying to shrink from cooling.
This happens even more with larger molds which often are cast at
relatively cooler mold temperatures. However, at the same time, the
metal core pins, being fairly small in bulk, are easily heated up by
the entering molten metal, and they have enough chance to expand from
heating before the cast metal solidifies, that they are then cooling
the same as the cast metal. However, they are not constrained by the
core in their rate of shrinkage, so can fully shrink. The casting
itself, however, is stretched slightly by the core inside, which has
nowhere else to go, and in that stretching, it also takes the hole
size with it, just as a dot or circle drawn on a balloon expands as
you blow up the balloon. Add in a little oxidation on the pins so the
pins and the cast metal don’t fuse, and you’re easily left with loose
core pins. The holes around the core pins simply weren’t allowed to
shrink quite as much as they might have “wanted” to.
The bottom line, Leonid, is that while you are indeed correct that
metal shrinks away from a hole on cooling, It is also shrinking by
the same percentage in every other direction at the same time,
including the much larger dimensions of the overall piece, which
overwhelms any slight expansion of the holes. That overall shrinkage,
however, since it’s always of a larger dimensioned article, will
overcome the shrinkage of a small detail like the metal next to a
hole. This is true even if the hole is almost as large as the overall
casting, such as casting a simple jump ring. The hole in that cast
jump ring will be slightly smaller than the hole in the wax model it
was cast from. Thermal shrinkage is a simple percentage of the linear
dimensions in all directions, unless the metal is physically
constrained by something else, such as pressure from the mold, or
stresses from uneven cooling, or the like.
And while there may indeed be situations where some other factor
related to the casting process that might degrade surface integrity
or dimensions (for example, an incomplete filling of the mold can
result in metal not quite reaching the sharp edges of a hole or the
end of a prong, or the like) might affect the hole size, most of us
have not found those effects to be such as to give us larger holes
upon casting. That’s true for ring sizes, and it’s true for the
holes into which stones will be set.
Leonid, I don’t question the fact that you have many years of
observation of the metal behind you in your career. But please also
understand that this is also true of many of the readers here on
Orchid, every one of which, at least from those many of us who’ve
responded to your thought here, have not found their/our observations
to be the same as yours. While I don’t suggest you’re stupid or
anything like that, I’d like you to also concede that we aren’t
either. More than a few of us have, in addition to extensive jewelry
experience and training, more than a little training in metallurgy as
well. You’re the only one who’s alleging that holes get larger
routinely as a result of thermal shrinkage. Might you consider that
if so many of us have directly observed the opposite, and that the
opposite also nicely fits any reasonable explanation of the way
metal shrinks upon cooling, that you just might have been explaining
your observations with the wrong conclusions? Could there be some
other factor in your processes over the years that could explain how
you’ve arrived at this belief? Might you perhaps have come to this
belief based on a few observations and have since simply assumed it
was happening even if it wasn’t actually doing so?
Just as you wonder how you seem to be the only one who’s experienced
this effect, many of us are wondering the same thing, only we’re not
assuming that our lack of observing this effect is due to our
inexperience, as you seem to be doing. We’re instead wondering how
you seem to have come to this conclusion that to us, contradicts
everything we’ve been taught, and have learned by experience, about
the way metal behaves. And I remind you that while some on Orchid
are newcomers and beginners, more than a few of the people who’ve
replied to this thread are quite assuredly not in that category, just
as you are not. While it’s always possible that you are the only one
in the group to know the truth, and the rest of us are wrong, that is
statistically rather unlikely.
Peter Rowe
When you heat metal it expands in ALL directions. A solid piece only has one direction available and that is out. With a hole in the piece, that would seem to be an avenue available for the heated metal to expand into. Does anyone no why it doesn't happen that way? Just curious after reading all the comments.
Let’s conduct mental experiment. Heat metal with a torch from one
direction only. The heat would be absorbed by the atoms comprising
the edge closest to the flame ( source of heat ). The distances
between atoms begin to grow. At the same time the atoms comprising
more remote parts will be getting less heat, or none at all. It would
be much easier for the atoms to move towards the source of heat than
away, because moving away would mean that they would have to push all
the atoms which are still cold. In nature everything happens in the
direction of the least resistance. So the edge would move towards the
flame. upon continue heating the temperature will equalize and the
rest of the atoms will expand in the direction where it will be the
easiest for them to move.
Another scenario. Chunk of metal with the hole in it. If we could
manage to heat only outside edges, then when atoms would gradually
expand towards the heat; the edges comprising the hole would be the
last areas to expand and the hole would become larger.
If we can arrange to apply heat only inside the hole, than hole
would be first to expand, and it would be easier for atoms to move
towards the center of the hole, making it smaller.
The real life situation would be the sum of all these factors plus
many more. This is an age old problem with which blacksmiths struggle
for centuries. Uneven expansion causes warping while tempering and
that is why in industrial setting metal is left for sometime to soak
the heat, after it reached required temperature.
The answer to your question is it depends on how heat is applied and
for how long. It is also a good place to mention that the rule that
solder always flows towards the heat is exactly due to this
phenomena.
Leonid Surpin
Hello Leonid, The pins in your sculpture expand while they are
heating up during burn-out. That is why they slide out of the mold
after casting. They had expanded more while hot than the cast metal
shrank while cooling.The hole in the coffee cake did not shrink
because the pan was in an expanded state while baking., holding the
hole’s diameter large while it was cooking. And because I ate the
center out of the thing before you saw it. Why are we even having
this conversation?
Tom Arnold
P.S. I too make models out of silver.
Everybody one time or another have had a cup of coffee with a slice of coffee cake in the shape of a ring. Such cakes are baked in round forms with hollow centers, to form a ring. Do you realize that if holes after cooling were getting smaller, there would be no coffee cakes in this universe, because these cakes would be impossible to separate from their forms.
As noted before, coffee cake reacts this way because the ENTIRE cake
is cooling at the same rate causing shrinkage of the ENTIRE cake,
thus causing the hole to stretch giving the appearance that the hole
is expanding, which it is but only because the rest of the cake is
shrinking. Maybe take 10 minutes and have some coffee cake and think
about this. We’ll do the same and go back to making shrink less holed
jewelry.
But as with rings, the overall shrinkage of the whole piece is greater, and the hole still does become smaller.
But I made my comments in context of invisible setting when stones
are cast in place. The cross-section of the rails would be the
widest from the bottom of one groove to another. That means that this
dimension would undergo the largest shrinkage, while walls of the
grooves, closer to exit would shrink less. In another words, if a
groove would be triangular with vertex angle of 60 degrees, after
shrinkage the angle would be maybe 70 degrees. It may be a small
change in dimension, but it is enough to guaranty that stone wold be
lost. If rails cross-section would be perfect square, and the piece
itself would have perfectly even mass distribution, then the outside
shrinkage would take care of the inside. But such jewellery does not
exist. The amount is relatively small, from wax to metal. If metal
master - mold -wax - casting - working masters - mold - wax -
casting, then as much as 20% compensation is used, depends how good
the caster is. But invisible setting presents a special problem.
However small amount of shrinkage is, it is enough to ruin your day.
Leonid Surpin
Does anyone no why it doesn't happen that way? Just curious after reading all the comments.
I think you didn’t read them all…
Yes, metal expands in all directions. But as many of us have been
trying to explain to Leonid, the overall expansion and contraction
of the whole piece, which is a percentage of the whole overall
dimensions, far exceeds any expansion of smaller details. You cannot
take just one tiny detail or dimension and look at in isolation from
the rest. When the metal expands, all of it is expanding in all
directions equally. The expansion is not constrained by solid metal
and more “allowed” by an open edge, just as upon cooling, the
shrinkage of metal away from the edge of a hole is not somehow
greater because there isn’t metal in the hole pulling on the edge.
The expansion or contraction occurs on an atomic scale, and aside
from distortion and stress caused by uneven heating or cooling, or
physical stress from external constraints, a hole or lack of it
doesn’t make a difference. The edges of a cooling hole, for example,
are indeed shrinking away from the center of the hole. But no more
than the metal at an equal distance from an undrilled point, since
in the case of the hole, all the metal is shrinking, including the
whole area surrounding the hole. The metal in an “undrilled” hole’s
edge is not being held back from more shrinkage as it cools, just as
the metal at an edge is not expanding more on heating just because
there’s nothing in it’s way. Since the entire mass is expanding, any
metal “in the way” of an expanding area is equally moving out of the
way due to it’s own expansion… Get it? You can’t isolate
individual areas and treat them as seperate parts of the whole. That
leads to confusion. (and this thread…)
Draw a circle, and a same sized solid dot on a balloon, and blow it
up a bit. Measure the two, and find they are still the same size.
Blow it up some more, and the same is still true. The ink, or lack of
it, doesn’t affect the expansion or contraction of the overall
ballon’s surface. Heating and cooling the metal causes expansion and
contraction in the same way, except in all three dimensions, rather
than the example of two dimensional drawing on the surface of a
balloon.
Peter Rowe
I suggest you think about it for more than 10 seconds then. Take a
sheet of metal, scribe a circle on it and heat the sheet. The sheet
expands of course, but what happens to the circle? It expands too,
obviously.
That is correct but it does not apply. When stones are cast in place, a hole never existed in cold state. It is created hot and when it cools off, the metal shrinks away from stones, and hole is getting larger.
Well Leonid, you deflected that one by saying that it didn’t apply,
but carefully didn’t respond to the second part of my post, which
was…
Now, using a very thin saw, cut the circle out and put it back in the hole. Now heat the sheet (and circle) the same as before. Do you really think that the hole gets smaller to pinch the circle, or do you think the circle gets smaller? Of course not; the hole and circle expand the same amount, and contract the same amount when they cool.
How do you explain that then?
Regards, Gary Wooding
It is also shrinking by the same percentage in every other direction at the same time, including the much larger dimensions of the overall piece
The other factor in Peter’s very reasonable post is exactly the
above - percentage. The Golden Gate Bridge expands and contracts 12
feet (4 meters) every day, justbecause it’s 1 1/2 miles long. One
percent of a 1" hole is a lot. One percent of a 1mm hole is very much
less. This discussion is (as usual) not about monumental sculpture,
it’s about setting 2mm stones into gold.
Leonid,
Holes get smaller on freezing and cooling.
I have made a few pen parts which include a 20mm tapered tube for
the nib end. Very critical inside profile. I made a steel mandrel
which I dip into molten carving wax, just like candle dipping. Wax
shrinks far more than metal, if my timing is off the wax splits.
Machine the outside of the wax and a draw bench will usually extract
the mandrel (without too many fatalities) Cast the wax in silver, and
it takes a big hammer or press to re-install the mandrel for finish
machining.
At every step of the process shrinking holes are a concern. With the
shrinkage rate of wax it is a naked eye effect, no fancy measuring
tools nor even magnifacation required to see.
jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
The fact that holes after casting are large, is very basic and mandatory adjustment that any modelmaker makes.
Well, no…
Leonid:
She’s right about the pins not sticking because of oxide buildup.
The sculpture professor in my undergrad classes had some secret
’mystery flux’ he put on the bronze pins to keep them from oxidizing.
When the castings were done, they were usually fused right in, and
could be ground over with no telltale marks. I don’t remember what it
was, (if I ever knew), but I’m betting it was mostly borax. White
paste, anyway. Even the ones that weren’t fused were very tight. No
way they were coming out short of drilling them out.
As far as coffee cake goes, what’s the coefficient of expansion of a
coffee cake? What’s the surface friction of the mould? Better yet,
the moulds typically have a draft angle on them. Perhaps this aids
in demoulding. Or perhaps the cake is soft and squishy. That’s what
they call an apples and elephants sort of analogy. I’m not sure how
they relate in any meaningful manner.
As far as masters go, yes, I’ve made masters for my production line
where I had to end up with cast-in-place bezel settings that had to
end up exactly on size, after the masters were cast, rubber molded,
injected, and then cast again. I took very careful measurements of
several test blanks at every step of the process from original
master to cast final pieces. The settings got smaller every time.
Regards,
Brian.