With the gantry design, the print bed and object are stationary, so there is movement of the mass there. There is no real need for the extruder to be any larger than the extruder of a desktop printer (using Wades Gears or similar), and that moves side to side, relative to the gantry. Provided that the gantry/X-axis assembly was rigid, there should be little wobble.

In this set up, for any particular layer, neither the Y axis (print bed) nor Z axis (in the +Z direction on each layer) moves as the layer is being extruded. Only the movements are the Gantry moving along the Y-plane and the X-axis assembly moving side to side. This printer is not likely to be used for printing small, high feature things like figurines. It is to be used where it is necessary to print long or wide things such as a bumper bar for a car.

Old Man Emu