A dual roll fabric welding or seaming machine is configured to seam pieces of sheet material to one another as the pieces move downstream. The machine includes modular gantries and various actor devices which may be readily mounted on any of the gantries to interact with the moving sheet material to achieve various functions, such as seaming pieces of sheet material together, forming hems, applying grommets to the sheet material, printing on the sheet material, connecting reinforcement strips or ropes to the sheet material and cutting the sheet material.