A weld overlay machine assembly includes a carriage to support a hinged index bar and a wire feed assembly. The index bar has an auto height control unit and an index assembly to locate the position of a weld torch relative to the index bar. The assembly is configured to adjust the index bar to interior contours of the vessel while applying a layer of overlay material to a surface therein. The assembly runs along a track in the interior of the vessel. The assembly is configured to transition from sides of the vessel to that of the top or bottom domes wherein the curve of the domes are perpendicular to that of the radial sides. This transition is done without the need to add or remove components to the assembly. This is accomplished by providing the pivoting of the index bar relative to the track.