Abstract: A welding carriage has a frame that is adjustable in width and height and is guided by the sides of a workpiece. First and second wheel assemblies support the frame upon the workpiece, the first and second wheel assemblies forcibly engaging the sides of the workpiece for guiding the frame along a path substantially parallel thereto. The frame comprises two opposing lateral sides interconnected by a linkage therebetween. The linkage can be actuated to adjust a coarse width of the frame, dimensional variations being handles by biased guide wheels of the second wheel assembly. Each of the opposing lateral sides further has vertically adjustable leg posts for adjusting a vertical height of the frame.