Yes, there IS really SOME shrinkage inn the metal, but the
controlled tests we ran for 3D Systems and their growing substrates
vs Kerr hard green wax indicated that the investment created more
"shrinkage" problems through expansion than the metals did via
actual shrinkage from the melt. The exceptions, as I recall, were the
Pt alloys, which gave the greatest shrinkage from liquidus to solid
In conjunction with that, I did a survey of 50 accomplished bench
people (and included my own vicarious experience in the repair and
manufacturing end). The question was:
Given the average ring casting, how much actual removal of metal
takes place in YOUR finishing process? No guesses, please, actual
It was a true learning experience for many, including myself. The
average was 0.3 mm, with care. In ALL cases, that exceeded any
differential caused by "shrinkage".
In the end, because we were in the business of selling CAD and CAM
solutions, including mills and "growing" machinery, our "suggested"
answer was to apply 7-10% upwards 3D scaling to the CAD model, and
experiment from there.
Concerning the creating of prongs and bezels in the CAD model (to be
cast), I have some serious reservations, but I'm sure you do, too. A
discussion for another time, perhaps.