edge defined internally by a slanted surface 10 shown in both fig1 and 2 for radially pushing against the similarly slanted surface of the pads 8 the radial compression of the pads 8 against the cartridge 6 is achieved by moving the cover of fig1 axially towards the body 7 by means of suitable tightening screws not shown so that the axial movement of the cover 9 causes radial thrust of the pads 8 against the external cylindrical surface of the aforementioned cartridge 6 advantageously the pads 8 of the upper elastic system have a cogged internal surface or with longitudinal recesses 11 which on one side lead to the outside through a circular slot 12 shown only in fig1 between the closure cover 9 and the upper end of the cartridge 6 while on the other side the longitudinal recesses 11 lead into an annular chamber or internal passage 13 formed between the cartridge 6 and the body 7 the chamber 13 in turn opens outwardly below the frame 3 through radial holes 13 39 immediately above the second elastic support system the second elastic support system comprises an annular element formed by circular elastomeric segments 14 as shown in fig3 arranged peripherally between the cartridge 6 and the lower end of the body 7 the segments 14 are suitably supported axially by an internal annular shoulder as can be seen in fig1 the cartridge 6 which supports the rotary spindle 1 extends axially below the hollow body 7 and correspondingly the spindle 1 extends beyond the lower end of the cartridge 6 with a leg defining the shaft 1 39 of the electric motor 5 according to the present.