imparted to the free portion 12 of the blade 10 a corresponding instruction is given to the step motor 42 to cause the displacement of the cylindrical rod 40 through the micrometric table 41 in order to impart said second angular displacement u03b2 to the free portion 12 of the blade 10 and then the cylindrical rod 40 is turned to an inoperative condition so as to allow the free portion 12 to assume a corresponding second plastic deformation position p2 which as a function of the first standard curve bending approach and with the corresponding correction for the specific second equation curve is situated within the values required for the specific application position p 2 can be the required final plastic deformation afterwards the blade 10 can be released from the fastening device 20 it should still be observed that the initial distance d 0 between the point of reference and the blade 10 in the original position is defined by the sensing device 30 and registered in the central processing unit 50 in order to be subtracted from the distance d 1 that was measured after the first plastic annular deformation of the blade 10 as illustrated in fig1 the central processing unit 50 can be operatively connected through an analog digital interface 60 to another sensing device 70 which is disposed to measure for example the seat deepness which is specific for each blade that is bent in order to determine the value for the plastic deformation to be imparted to each blade 10 as a function of at least one dimensional variation in a respective piece or element that is going to be associated to each particular blade in another embodiment the determination.