Abstract: An apparatus and a method are provided where two relatively rotatable plastic tubes in telescoping relation are welded together at their telescoping, contacting interface. In practicing the invention, soft and flexible thermoplastic tubes are fitted in telescoping relationship, one inside the lumen of the other. Gripping jaws compress and shape the outer tube uniformly which stiffens the inner and outer tubes and defines a contacting interface. Axially spaced from the interface, the inner tube is chucked with shaping jaws to impart a polygonal, cross-sectional shape to the inner tube. Frictional heat generated by rotating one tube relative to the other tube softens the interface allowing the tubes to weld together when rotation is stopped.