Success at last! The SES has taken a lot of trial and error, but I'm now ready to go into production thanks to a breakthrough in the casting process.
The foam part right off the CNC machine.
What I didn't show is how I invested the foam part in a mixture of plaster of paris and water putty. This formed a high temp shell around the part that will keep the sand from collapsing in while the foam is lost. It also results in a super smooth finish on the part. Here you can see the shell that surrounds the aluminum piece. As the aluminum cools and contracts, the shell fractures and is easily removed.
Chipping away the shell to reveal the excellent finish and detail.
After about ten minutes of machine work, the part is done!
I now have the part and process refined enough to be able to produce these parts quite easily.