The present disclosure provides three-dimensional (3D) printing systems, apparatuses, methods and non-transitory computer readable media for the production of at least one desired 3D object. The 3D printer described herein comprises, inter alia, an opening that comprises a first side and a second side. A component of the 3D printing, such as a layer dispenser, may be conveyed from the first side of the opening to the second side of the opening (e.g., and vice versa) during the 3D printing. The opening may be closeable. A closure of the opening may seclude the component during at least a portion of the 3D printing. Additional features relating to components of the 3D printing systems are described herein.