"How much do sculpts 'shrink' when they are cast?" Topic

Hi all
I've been told by a friend that when a mould is made of a sculpt, anything cast from it will be smaller than the original, because of shrinkage. How much shrinkage occurs?

If for, instance, the original green is 30mm high, how high would the final metal mini be? (Or vice versa if that's easier to find info on).

If there is going to be shrink, then they usually get "flattened" across the plane of the mold.

So normally then don't get shorter, but skinnier.

The amount of "squash" is dependent on the mold material and the ability of the mold maker.

Regards, the Gorb

Gorb is correct, they don't shrink n height – it is the pressure of the mouldmaking and casting process that flattens them.

Mike

But isn't flattening a separate issue?

At Historicon last year (IIRC), I mentioned to Mark Sims that his new Punic Wars figures were not as beefy as his WW2 or SYW figures (a good thing). He replied something to the effect that the molds for the dollies had shrunk a bit.

from "Principles of Centrifugal Rubber Mold Casting"

"The average shrinkage for CRMC molds is usually figured at 10% in ther vertical dimension and 1.5% in the horizontal dimension" The goes on to note that all shrinkage is dependant on the material of the master being used, the compound of the rubber mold being used, as well as the heat and pressure applied.

Any company that sells rubber molds will also supply you with a tech sheet that will tell you what the shrinkage is based on heat and pressure applied to that particular rubber mold.

I know that when I was making molds using the equipment at a fishing tackle business, shrinkage was and important factor for them to consider due to truth and advertising laws – a quarter once jig needed to weight a quarter ounce when finished.

There are a lot of misconceptions on this subject, a lot of received wisdom which is quite wrong.

If you have production and the original of a figure (as I have many examples to hand) and a micrometer this is what it will tell you.

Change in dimension parallel to mold separation and centrifugal force from original to final product (usually the height of the figure)- none, sometimes there is a slight elongation.

Change in dimension parallel to mold separation but perpendicular to centrifugal force from original to final product (usually the width of the figure) – one to two percent.

Change in dimension perpendicular to the plane of mold separation from original to final product (usually the figures' thickness)- six percent or more.

Thank you all! Much appreciated.