A die for forming a lost wax ceramic core allows the formation of non-parallel separating spaces between adjacent portions of the core. The core will eventually form cooling channels in an airfoil. The die for forming the core includes a plurality of moving parts having rib extensions. At least some rib extensions are non-parallel to form the non-parallel spaces. The die includes two main die halves that come together to form several of the spaces. Inserts move with those die components and come together to form other spaces. At least one of the inserts contacts surfaces on one of the die halves, such that the non-parallel spaces are formed.