rod 84 and into engagement by the folding clamp 92 followed by folding and clamping of the other ribbon end 87 the result shown schematically in fig2 is a bow preform 101 which is symmetrical about a line of symmetry 102 extending generally perpendicular to the length of the center portion 80 of the ribbon material the bow preform 101 which is held in light tension is then gathered on its center by squeezing it between a pair of opposed horizontal gathering slides 103 the slides squeeze together the center portion 80 of the preform simultaneously with the overlying ends 87 the gathering slides 103 moving linearly on the line of symmetry 102 the result is shown schematically in fig2 where the gathering slides 25 are shown closed to form a center gathered portion 104 to retain the portion of the bow preform 101 while it is being squeezed between the gathering slides 103 and to prevent the bow material from moving vertically out of the slides as a result of its inherent resilience one of the gathering slides 103 includes a retaining slide 105 which precedes closing movement of the gathering slides and extends over the center of the bow preform to retain.