the rotation speed again rises above the threshold value a reverse switching of the electrovalves 41 42 connects the first chamber 35 to the pressure source p1 whilst connecting the second chamber 36 to the deflation orifice 44 so that once again a pressing force f can be exerted the pneumatic sensor 19 is useful for completing the measurements of the tachometer 17 in the case of very large burrs it is then to be feared that the retraction of the milling cutter 1 will not be sufficiently fast due to the reaction times of the control means the pneumatic sensor 19 makes it possible to anticipate these burrs and initiate beforehand the removal of the cutter 1 when the milling cutter 1 passes over the start of a blocking burr 5 it is progressively retracted by a sequence of switching operations as the oscillatory movement produced can be very fast use is made of the shock absorber 9 for attenuating it and for making the switching operations less frequent thus the shock absorber 9 constitutes a jack whose cylinder is connected to the robot 3 and whose rod is connected to the spindle 2 and whose chambers are interconnected by a narrow passage bypass 45 makes it possible to limit chattering the use of a regulatable shock absorber makes it possible to fix the release speed of the milling cutter given.