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[Source] Shrinkage rulers


#1

Greetings!

I’m learning bronze, silver, copper and brass casting, both lost wax
and sand casting.

One of the sand-casting books I was reading (“The Complete Handbook
of Sand Casting” by C.W. Ammen) mentioned special rulers that are
marked to account for the metal shrinkage.

In effect, you make your mold 1" by the ruler, but you’re really
making it the shrinkage percentage larger than 1". Sure seems a lot
simpler than doing the shrinkage math for each dimension!

Anyone know where I can buy rulers like that for bronze, copper,
silver and brass?

(I suspect bronze and brass % vary based on the exact formulation,
but it doesn’t hurt to ask.)

Thanks in advance.
v/r
David Wendelken


#2

David, A possiblilty whether or not you find the actual shrinkage
rulers…If you know someone, or you, have access to a computer
drafting program, “draw” a ruler, any length. Then, that drawing may
be scaled to the proportions you need. Print out the various rulers
and carefully identify each one. Actually, as I think about it, you
may be able to accomplish the same thing by scanning a ruler. By
scanning you can control the ratio of the image and not deal with
distortion that a camera is prone to. Be careful that the printer is
calibrated 1:1 for this to be accurate [usually a simple process]With
this process it is an easy matter to have multiple scales for the
metals you mention as well as other metals such as the metal clays.

Orchid Rules!
Karla in Southern California on an odd 90 degree November day.


#3

I think you are probably chasing windmills. Shrink allowances would
be on the order of 1/4 inch per foot. This becomes important with
large engineered castings that will have machined surfaces to fit
together. These will also need a machining allowance added to
compensate for the material that will be removed. Small art castings
are not as critical. CAD drawings can be automatically adjusted for
shrink in the program. If you are making Dental or Medical implants
by investment casting you may find dimensional control very
important.

jesse


#4
In effect, you make your mold 1" by the ruler, but you're really
making it the shrinkage percentage larger than 1". 

I’ve read Ammens, too, but I didn’t catch the part about shrinkage
rulers -never heard of them… And as one pointed out today, on a
12mm part it’s almost immeasurable anyway. 3 feet, yes. Anyway, there
are scaled rulers available at any art store. They are the triangular
rulers that architects use, or used to before computers. One edge
measures 1/8 scale, one does 1/16 scale, etc. Meaning that 1 inch on
the ruler actually measures 7/8", or whatever, but you use it
consistently and your drawing comes out to 1/8 scale. It’s not really
a “shrinkage ruler” though…


#5

In 1975 I moved to Manitou Springs Colorado. The new highway had
bypassed downtown and it had gone into a decline as most of the
tourist just drove on by on their way to Cripple Creek and beyond.
So the tourist and curio shops were often only open for a limited
time and some rarely opened. There was this one shop near the end of
the main drag that had its windows covered over but if you looked in
past the shades you could see machine tools. Every now and then you
would see this crusty old guy who looked older than god go in and out
of the shop. Somewhere in that time I managed to get in way over my
head on a casting job for some belt buckles. I was supposed to modify
a copy of an old US cavalry buckle with the company and platoon
for a group over at Ft Carson. I thought since in knew
how to investment cast I could just transfer that knowledge over to
sand casting these buckles since I did not have any investment
casting equipment of my own at that time. Well I was making these
horrible buckles and really getting worried as I had taken a deposit
from the soldiers and these buckles I was making sucked. As I was
fretting about this I was told by a friend I should go talk to old
Bill in that shop at the end of the avenue because he knew all about
casting. I was desperate and so I went over to the shop and knocked
on the door and Bill answered he would not let me in but he listened
as I told him my tale of woe. He said he might be able to help and
locked up his shop (I never did get to see the inside of that shop)
and came over to where I was working on my castings. Over the next
few days he proceeded to teach me how to do fine sand castings with a
match plate to hold the model so you could rapidly ram up a flask
with all the gates and runners already formed, he threw out my
terribly course sand and gave me fine grain sand that was very
similar in texture and fineness to the Delft Clay sand and quite a
bit of other advise. I finally got those buckles done and learned a
lot along the way from old Bill. It was only years later when I saw
and read his books that I realized how lucky I was, old Bill was C W
(William) Ammen.

Anyway he would have used those shrinkage rulers on large sand
castings as others have mentioned. If you want to learn more about
pattern making for sand casting of course read Bill’s books but you
can also download the old US Navy rate training manuals for
Patternmaker 3 and 2 at

it has a lot of good on making precision patterns.

It discusses the use of shrink rulers you needed one for each metal
as there are differences in shrinkage for each alloy. THey were on
the order of 1/10 inch per foot for cast iron or 3/16 per foot for
brass etc. I doubt anyone ever made one for the precious metals.

James Binnion
James Binnion Metal Arts


#6

The technical name is “contraction rulers” Try searching under that.
Here is an example of a supplier

http://www.tridon.com.au/Products/Product.aspx?SG=5&S&G=556&P=64330

kay


#7
Anyway, there are scaled rulers available at any art store. They
are the triangular rulers that architects use, or used to before
computers. 

I own a shrink rule for brass (seems to work for bronze too), iron,
and a double shrink for iron, but it would be impractical to use for
jewellery. Does anyone have one for jewellery and precious metals?

Regards Charles A.


#8
The technical name is "contraction rulers" Try searching under
that. Here is an example of a supplier 

My US Navy Pattern Maker Training Manual calls them shrinkage rulers
or contraction rulers in the illustration caption showing them so my
guess is both terms are correct and depending on where you live and
who you learned from one or the other term would be prevalent.

Jim

James Binnion
James Binnion Metal Arts


#9

My brother was a model maker for the pottery industry for several
years. While he was working for one of the larger china manufacturers
they had to switch from one shrinkage factor to a slightly different
factor, something like 4.5% to 5%, because the clay in their mine was
just ever so slightly different as they worked their way into a
different level of the deposit.

Here is what he had to say about where to get shrink rules:

"Milligan’s Hardware in East Liverpool Ohio might have them. They
used to have all kinds of potter’s tools. If you want the old
fashioned kind, they would be the place.

If you want a modern shrinkage rule, Creative Industries makes them
and sells them through many of the pottery supply places. I did a
search on “shrinkage rule” (not ruler) and got several hits.

The danger of having a shrink rule around is that people will pick
it up and measure things, thinking it is a regular ruler." Bill
Walker

Stephen Walker


Andover, NY


#10
My brother was a model maker for the pottery industry for several
years. While he was working for one of the larger china
manufacturers they had to switch from one shrinkage factor 

It’s already been said that most jewelry is too small to use a ruler
with, anyway - depends what work a person is doing, ultimately. The
typical way to do the same in jewelry is through measurement. I grew
up with an 8% shrinkage factor in model making - some use other
numbers, but they’re not far away. That’s from a model, through
vulcanized molding, and the casting process, not just casting alone.
What that means is that 2.2mm will become 2mm, 1.1mm will become
1mm, etc. You don’t really need to do calculations because the
fractions get so tiny that they don’t matter in normal circumstances
of jewelry. Jet fighters, yes, jewelry generally not. Since it’s
largely about proportion, if you make a 2mm thick shank and 1.5mm
prongs (whatever), and scale the rest to your base aesthetically,
then you’ll have it.

The tool of choice for that work, and general jewelry too, is called
a degree gauge. I won’t link it, but one is Otto Frei #135.012. You
could also use vernier or digital calipers, and might. There’s a
couple of advantages to the degree gauge, though. First is that you
can measure inside things, because of the opening. So, you can
hollow out a signet-type ring, and measure the wall thickness around
the outer edges. Another is that the small tips let you spot check
here and there, where a caliper will only get the average or mean
dimension. Hand tool for all sorts of things- I use mine every
day… Make sure you get millimeters and not lignes - those are for
watchwork…