Rocker, as part of my apprenticeship at GE back in the 60\'s I spent a stint in their foundry. Patternmakers use what are known as contraction rulers. They have thermal contraction values built into them. They came in a variety for different thermal contraction rates, 1%, 2% etc. They allow you to build patterns without having to constantly add the contraction rate to each measurement. I\'ve also built a lot of injection molds, and the first thing you would have to do is add the shrink factor to every dim.
Gary