In Pictures: 18 supercool objects made with 3D pri...
3D printed chain and sproket
This chain and sprockets were not printed separately. Typically, 3D printed objects with moveable parts will include small support structures (pillars of polymer or metal) that hold movable objects in place during the printing process. Once printing is completed, those support structures can then be cut or blasted away with a water jet. Often, objects are also hand-sanded to provide a smoother surface.
In Pictures: 18 supercool objects made with 3D printers