An assembly for use during manufacture of a balloon envelope that includes a table having first and second levels, an indicator disposed on the first level and a sealing component. The first level is arranged to receive a first sheet portion of material. The indicator is arranged along a lengthwise axis of the table to indicate a position for attaching a tendon to the first sheet portion. The second level is arranged to receive assembled gore portions of the envelope comprising the first sheet portion, the tendon and a second sheet portion material. The sealing component is configured to move along the table and to apply a heat seal to bond together the first and second sheet portions disposed thereon in order to form at least part of a gore portion of the envelope, such that the tendon is arranged proximate to a centerline of the gore.