There are several ways to do this. We chose to make a vacuum-formed plastic sheet mold. We then poured two-part plastic resin into the vacuum formed mold in order to create the blank for milling.
Using this technique, it is possible to create complex blanks that may have very unique shapes. This makes it possible to decrease the amount of material that needs to be removed by the CNC milling process.
The platform that we use is a Home hobby vacuum forming unit that was easy to build and very inexpensive.