For making orthotic braces and prosthetic devices, vacuum shaft mandrels and foam workpiece blanks are pre-fabricated to a standard design for repeatable assembly and disassembly. A mandrel is easily installed in a workpiece blank, or reinstalled in a previously made mold body. The mandrel is likewise easily removed from the mold body and returned to stock after the mold is made and the required brace is completed. Mold bodies are storable for reuse with a mandrel of the same design for the next vacuum forming brace making operation. A limited supply of standard size mandrels can thus be used for making and serving any number of mold bodies. One mandrel size accommodates a range of mold sizes.