urethane tooling board. There are quite a few different ones, but they're all basically the same thing - a high-density urethane foam. The higher the density, the more detail the material will hold, and the less porous its appearance. Of course, the denser it is, the more it costs too. It's totally even - no grain, no color variation in a piece.
Look for Renshape (Freeman Supply), Butterboard (Golden West Mfg), Precisionboard (Coastal Enterprises) etc.
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[QUOTE=cjjonesarmory;857337]I've worked a lot with metal, but doing 3D carvings is a lot newer for me. I've done a lot, ok SOME, 3D carving in wood, primarily oak, but I want to work with something that's going to look a lot more "even". For example, take a look at the image in the following link. I would imagine it's plastic or wax, but I wouldn't know where to begin to buy such materials suitable for machining.
I have made mechanical parts from Acetal and also from HDPE, but they don't really seem like great materials for carving. I want something that looks a lot like the materials on the site: