BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a bar magazine for lathes equipped with a bar-centering instrument designed principally to attenuate the vibrations of the bar in the loading channel and in particular during high speed machining of small-diameter bars. 
   2. State of the Prior Art 
   The problem of avoiding vibrations of bars in the channels of magazines and holding them in the correct position during machining in lathes (for example a plurimandrel lathe) is known in the prior art. In particular, there are serious problems when the bars have a diameter much smaller than that of the magazine channel and when the machining is done at high rotation speeds as often happens in the more modern machines. Under these conditions, indeed, the vibrations are quite accented and, in addition to causing considerable noise, they lead to the production of machined pieces out of tolerance. 
   To remedy these problems it is proposed to insert adaptors to be fitted in the channel so as to leave little freedom of movement to the bar and thus reduce its vibrations. However, this solution brings on the need to replace the entire bar-pusher each time it is desired to machine a small-diameter bar. This fact, in addition to the need of having available several bar-pushers with different dimensions, also involves the need to stop the machine for long periods to insert the adaptors in the channel and change the bar-pusher. It is also noted that when the bar is shaped (for example with a hexagonal or square cross section) the diameter reduction proposed in the prior art causes considerable vibration problems contrary to what is desired. 
   The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a lathe bar-magazine which would avoid strong vibration of the bars, even when their diameter is much less than the diameter of the channel and the rotation speed of the bar is high, while avoiding having to stop the machine for long periods when changing the diameter of the bar being machined. 
   Another purpose of the present invention is to make available a bar magazine for lathes that while ensuring satisfactory centering of small-diameter bars in the loading channel would keep a simple and economical structure compared with prior art magazines. 
   SUMMARY OF THE INVENTION 
   In view of this purpose it was sought to provide in accordance with the present invention a mono or plurimandrel bar magazine for lathes including at least one channel designed to receive in it a bar being machined and pushed along the channel by a bar-pusher collet with said magazine including at least one bar centering member arranged in a zone along the channel and characterized in that said centering member is movable upon passage of the collet in said zone between a first position of engagement with the bar for its centering in the channel and a second position removed from the bar to allow passage of the bar-pusher collet through said zone. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To clarify the explanation of the innovative principles of the present invention and its advantages compared with the prior art there is described below with the aid of the annexed drawings a possible embodiment thereof by way of non-limiting example applying said principles. In the drawings: 
       FIG. 1  shows a perspective view of a part of a bar magazine for plurimandrel lathes with the centering member engaged on the bar; 
       FIG. 2  shows a detailed view of the centering member in the engaged position; 
       FIG. 3  shows a view of the centering member in the position removed from the bar; 
       FIG. 4  shows a view of a part of the magazine with the centering member raised; and 
       FIG. 5  shows a view of a part of the magazine when the loading channel is opened. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the figures,  FIG. 1  shows a portion of a bar magazine in a plurimandrel lathe. In particular said FIG shows a loading channel  11  and, beside it, two other loading channels  111  and  121  shown only partially. In channel  11  is arranged a bar  15  being machined having diameter considerably less than the diameter of the channel  11 . Said bar  15  for example could rotate at high speed as often happens in the more modern machines. 
   The bar  15  is upheld at one end by the bar-pushing collet  16  which is designed to run in the channel to advance the bar being machined in the magazine. Said collet  16  is prior art and not further described. At its opposite end the bar  15  is supported in a mandrel of the lathe (not shown in the figure) arranged near one of the workstations of the plurimandrel lathe (not shown). 
   Advantageously the channel  11  is made in two parts, to wit an upper  12  and a lower  13 . The upper part  12  (having a virtually semicylindrical half-shell form) is movable with respect to the lower part  13  to allow opening of the channel at the end of machining and loading of the machine with a new bar to be machined. 
   In one embodiment of the present invention the channel  11  similarly to the other channels of the magazine is provided with an open portion  14 . Opposite the open portion  14  is arranged a centering member  17  designed to engage with the bar  15  being machined to hold it in the correct position in the channel and attenuate its undesired vibration. 
   The centering member  17  as shown in  FIGS. 2 and 3  includes a fork  17   a  fastened rigidly to a body  17   b  through a generic fastening member  23 . The fork  17   a  is movable between a position of engagement with the bar ( FIG. 2 ) and a raised position removed from the bar ( FIG. 3 ). This movability is made possible by the hinging  28  of the body  17   b  to the support  21 . Said support  21  is fastened to an arm  22  which is in turn fastened to the frame of the magazine. It is noted that in one embodiment of the present invention the arm  22  and the support  21  are fastened so as to be integral with the movable upper part  12  of the channel  11 . 
   In the position engaged with the bar (see  FIGS. 1 and 2 ) the fork  17   a  is arranged perpendicular to the bar while in the removed position it takes a position virtually parallel to the bar  15 . It is noted that these two positions are steadied by the action of a spring  20  fastened at one of its ends  25  to the body  17   b  of the centering member and at the other end  24  to the support  21 . Advantageously the body  17   b  of the centering member includes appropriate even surfaces for engaging permanently with the support  21  in the two aforesaid positions of the fork  17   a . It is noted that the fork  17   a  preferably has at the ends of its arms two bevels  26  designed to aid insertion of the bar  15  on the bottom of the fork  17   a . Expediently the bottom of the fork is shaped in an arc of a circle with a diameter slightly greater than the diameter of the bar to be centered. For example, the diameter of the bottom could be approximately 3 to 4 tenths of a mm greater than the diameter of the bar to be centered. For example, the diameter of the bottom could be approximately 3 to 4 tenths of a mm greater than the diameter of the bar. It is also noted that the fork  17   a  can be made of plastic, for example DELRIN. 
   In its position raised from the bar the fork  17   a  is arranged outside the volume swept by the collet  16  inside the channel  11  when the latter moves to push the bar  15  along the channel  11 . On this point, see  FIG. 4  showing the fork  17   a  in its raised position removed from the bar. When the collet  16  advances along the channel  11  it touches with its front part the fork  17   a  and moves it against the action of the spring  20  until it causes it to be released from the position engaged with the bar at the steady position removed from the bar and parallel thereto. In this manner the collet  16  can pursue regularly its travel along the channel  11  without the need of a smaller collet as occurred with the adaptors inserted in the channel in accordance with the prior art.  FIG. 4  also shows collet moving means  30  known in themselves and therefore not further described herein. 
     FIG. 5  shows the opening step of the channel  11  when machining of the bar is finished and a new bar is prepared for loading and machining. The presence of an L-shaped striker  19  fastened integrally to the fixed lower part  13  of the channel  11  is noted in particular. When the movable upper part  12  rises to open the channel, it is dragged behind the centering member  17  that goes to touch the striker  19 . As shown in the figure, the fork  17   a  is then made to again spring into its position perpendicular to the extension of the channel  11  ready to engage with the new bar that will be loaded in the channel. 
   It is now clear that the preset purposes have been achieved. Indeed, a bar-magazine for lathes (in particular for plurimandrel lathes) allowing centering the bar being machined in the loading channel even when the bars have a diameter considerably smaller than the channel diameter and avoiding strong vibrations during machining has been realized. This result was achieved without the need of setting up the magazine (for example by replacing the bar-pusher or inserting adaptors along the channel) each time the diameter of the bar being machined changes. This way, long stops in the machine causing reduction of productivity of the machinery are avoided. In addition, the magazine in accordance with the present invention has kept a simple and economical structure as a whole with the only addition being a simple centering tool that is operated and made to spring into its operating positions by using the movements that were already called for in the lathe&#39;s machining cycle. 
   Naturally, the above description of an embodiment applying the innovative principles of the present invention is given by way of non-limiting example of said principles within the scope of the exclusive right claimed here. For example, depending on the type of magazine, the centering members arranged along the channel could be more than one. The fork could be made in two parts to be able to adjust the breadth of the fork and ensure correct restraint of the oscillations of the bar even when it is desired to machine bars with different diameters.
A bar magazine for lathes includes at least one channel designed to receive a bar being machined and pushed along the channel by a bar-pusher collet. The magazine includes at least one bar centering member arranged in a zone along the channel. The bar centering member is movable, upon passage of the collet in the zone, between a first position of engagement with the bar for to center the bar in the channel and a second position removed from the bar to allow passage of the bar-pusher collet through the zone.