A three-dimensional printer for manufacturing additive printed parts includes a housing defining a cavity and first and second fixed rails extending along a first axis. First and second movable rails extend along a second axis and move independent of other another along the first axis. First and second print heads move along the second axis on the first and second movable rails, respectively, and first, second, and third dividers collectively separate the cavity to partially define process and instrument chambers. The first divider is mounted to the housing and the first movable rail and expands and contracts with the movement of the first movable rail. The second divider is mounted to the housing and the second movable rail and expands and contracts with the movement of the second movable rail. The third divider is mounted to the movable rails and expands and contracts with the movement of the movable rails.