insertion of a lightguide preform into a tube without contacting the sides thereof is accomplished by first roughly aligning the rod in spaced axial alignment with the tube . thereafter , the offset of the rod from the axis of the tube is measured and the amount of lateral movement of the rod from the axis is determined . then the rod is moved laterally in accordance with the determined amount of movement to precisely align the rod with the tube . once alignment has been achieved , the rod is inserted in the tube and the tube is collapsed thereabout . an apparatus for practicing this method is disclosed .