I build this as a game for my children. They love it. The parts were designed with freeCAD, to chek the assembly I load all stl files to Blender. All parts were bonded to a wooden panel with Epoxy. First I glow the spirals together. For this there is a hole 10mm inside, so you can put the spirals on a shaft. The bearing brackets do have a recess, this should be on the side of the Spiral Bevel Gear. The marbles should have a diameter of about 15mm. All Parts are designed in a way that they need only a litle bit support material.