I’m interested in your process. So if understand right, you are milling insulation foam?
http://www.homedepot.com/p/Owens-Corning-FOAMULAR-1-2-in-x-4-ft-x-8-ft-R-3-Squared-Edge-Insulating-Sheathing-36L/100320356
I have done some modeling with the stuff before with hand tools, but always figured milling it would not yield good results.