Abstract: A welding machine for welding the terminals of condenser or boiler tubes to plates, automatic in action and self-supporting by reason of an arbor assembly including elongated bar elements, ball bearings and the like, adapted for positive engagement of the interior surface of the tubes adjacent to the terminals and also at points spaced farther along the tube to assure stability of anchoring of the machine with the arbor assembly as its sole support, a motor being operatively connected between the fixed arbor assembly and the frame or body for 360.degree. rotation of the welding tip around the welding seam line where the tube terminals extend slightly beyond the surface of the apertured plate of the condenser or boiler, thus utilizing the terminals and plate.