a plurality of printing heads each having a surface formed with a plurality of output orifices and controllable to dispense the construction material through each orifice independently of the other orifices;

a shuttle to which the printing heads are mounted;

a support surface; and

a controller adapted to control the shuttle to move back and forth over the support surface and as the shuttle moves to control the printing heads to dispense the construction material through each of their respective orifices responsive to the data to form a first layer on the support surface and thereafter, sequentially the other layers; wherein

each printing head is dismountable from the shuttle and replaceable independently of the other printing heads; and wherein

each printing head comprises at least one registration structure that matches a registration structure in the shuttle when the printing head is mounted to the shuttle, wherein the shuttle registration structure is different for some printing head mounting positions such that the orifices in the such mounted printing heads are offset relative to orifices of at least some other printing heads in the cross-printing direction by less than a distance between two neighboring orifices on one printing head, wherein the cross-printing direction is a direction parallel to the support surface and perpendicular to a printing direction.