fig6 obviously in this embodiment of the invention the only shifting per mitted between the lower portion of the mold and the supporting longitudinal members is a rotation about the axis x x in a variation of the machine of the invention the pair of supporting elements in correspondence to each table is substituted by a single annular supporting element 16 that is coaxial with the axis of the mold wherein the above concave and cylindrical surface now becomes a concave portion of the spherical cap the above element which shall be called a drum is indicated and shown in a perspective view in fig7 correspondingly also the convex cylindrical surface made on the tables transforms into a convex surface constituted by a portion of the spherical cap coupled with the concave surface of the annular supporting element that is fixed on the frame in this form of realization of the invention rotation is possible see fig7 both about the axis x x and about the axis y y as well as about the axis z z with the fact always holding good as to the meeting point of the three axes remaining stationary with respect to the plane iii iii under the combined effect of the thrusts directed downward towards the base exercised at the extremity of the beam and the counter thrusts exercised by the mold at two intermediate points at the above extremities the beam bends upwardly assuming a curve which cavity is turned downwards symmetrically with respect to the mid plane of the press orthogonal to the plane of symmetry iii iii and passing through the two molds as shown in fig4 and 5 in.