force sensors all tests causing force to intervene are transformed into pusher movement tests moreover it will be noted that lt lt intelligent gt gt control unit 31 can according to the indications of first sensor 30 measure the total of the axial plays existing in the feed device in particular in chain 25 and between the latter and rotating clamp 23 by effecting a back and forth movement while bar 2 is blocked then it takes account of this measurement to calculate accurately each axial position of the bar when lathe 3 is of the type having a moving headstock unit causing the bar to advance and move backwards during machining of the piece a large axial play can thus be arranged greater than the length of the part to be machined between the pusher and the chain in order for this latter not to be driven by the movements of the headstock unit during machining the fact that first sensor 30 is an absolute encoder i e always indicating an angle with respect to a zero position has the advantage of letting control unit 31 know the position of pusher 20 at all times independently of the length of bar 2 one could however replace this encoder by a non absolute incremental encoder and program the bar feeder to effect an initialization maneuver by putting the pusher against a stop which defines its zero position but for reasons of reliability this maneuver would have to be repeated periodically it should also be noted that rotating camshaft 12 described hereinbefore could be replaced by a sliding camshaft fulfilling the same functions and driven longitudinally by a pinion and rack mechanism or a similar.