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Hello,

I am getting ready to build some master patterns and would like to know current thinking on upscale precentages to account for material shirinkage. i remember hearing 3% for investment castings years ago.

i am thinking a brass master for spin casting cerro bend, and or pewter. another oportunity is to make strene masters and have lost wax brass masters made from them, then pewter.

your thoughts please.

Al P.
 

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I think a pattern maker's rulers allow 3/16" per foot for
brass/bronze. Which is about 1.6%. If you are doing spin cast Gauge 1 sized
parts you probably don't need to worry about shrinkage. The spin caster will shoot the metal into the mold and overcome shrinkage. I used to spin
cast jewelry, never noticed anything shrink.
 

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Many moons ago when I was modeling in O scale, Precision Scale told me to use 3% for small parts and 8% for large parts. I could never get a real clear definition of which were small and which were large, but I would have to assume that most of what we would be doing in large scale would be considered large in their terms. Give them a call, the worst they will do is not talk to you.

Bob
 

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Cast silver and gold rings we figured 5% either spin (Centrifugal) or Vacuum assisted from wax to devesting (plaster of cast). The rubber mold and wax shrinkage was another 5%
Was handy to know as one could beat the old copyright stuff by a change of 10%... (30 years ago)
Thickness is the deciding factor.

What is the product? Pewter isn't very strong...

Shrinkage occurs during the cooling process, after the sprue has solidified and no longer feeds the object This is when some porosity can occur.

Different metal have different rates.
 
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