A mandrel assembly is provided for insertion into a hollow tube to support the interior walls of the tube during bending of the tube in a tube bending apparatus. The mandrel assembly includes at least one mandrel segment that is adapted for positioning within the tube and has an exterior support surface for supporting the interior walls of the tube during bending. The mandrel segment is anchored at a fixed axial location within the tube by an anchoring device that is radially expandable and retractable between an expanded condition in which an anchor shoe is engaged with the interior wall of the tube and a retracted condition in which the anchor shoe is loose within the tube. A mandrel support rod is attached to the anchoring device for inserting and withdrawing the anchoring device into the tube when the anchor shoe is retracted.