If you’re helpless to know the difference, then check out [Eric Strebel]’s 9-minute masterclass teaser video on making a two-part mold for resin casting, which is also embedded below.

Rapid prototyping uses three-dimensional (3D) computer aided design to quickly fabricate a part or, alternatively, a sand mold for casting a part from metal ... 3D layering and CNC machining system.

With the core loaded into the mold, urethane resin is poured in through the top ... the mold can easily be taken apart to reveal the newly cast wheel.