Abstract: Very large diameter metal shafts for turbines and electric generators, and other large structural metal parts, can be made in one piece to a high quality without occlusions, cavities, segregations, and cracks by building the part up layer by layer, each layer being formed by deposition of molten metal by welding along neighbouring tracks which together cover the area over which the layer is to be deposited. The weld deposition of the metal may be effected by a welding head which is moved longitudinally along the part, and if the part is simultaneously rotated the metal is deposited along a helical path in forming a layer. A plurality of welding heads may be used so that metal is deposited simultaneously at different positions during the construction of each layer.