A preform from which lightguide fiber is drawn is made by depositing optically suitable layers of doped silicon dioxide on an inner wall of a rotating glass substrate tube which is exposed to a moving zone of heat during a deposition mode and during a collapse mode. During at least a first pass following the deposition mode, a contact device is caused to engage each successive increment of length of the tube during exposure to the zone of heat. The contact device causes any sagged or offset portions of the tube to be reconfigured and causes the tube to have a central longitudinal axis which is a straight line which extends between stocks of a lathe by which ends of the tube are supported. The contact device may also be used to cause the tube to have a predetermined configuration along its length. The position of the contact device relative to the maximum temperature within the moving zone of heat for each increment of length of the glass tube allows the shape of the tube to be changed and allows that shape to be retained.