Abstract:
Machine tool with: a bed furnished with a base and two side walls provided standing along respective left and right sides of the base; a first saddle composed of a rectangular frame, with vertical sides provided perpendicularly and transverse sides provided sideways, and both ends of the frame sideways being supported on rear faces of the side walls so as to be perpendicularly movable; a second saddle arranged within the first-saddle frame and provided to be movable sideways, and having a front-to-rear penetrating through-hole; a spindle head arranged in the second-saddle through-hole and provided to be movable back-and-forth; a tool-retaining spindle supported, by the spindle head, with its axis paralleling the front-to-rear orientation and rotatable about its axial center; and, arranged on the bed, a table on which workpieces are set.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to machine tools furnished with: a bed; a table on which workpieces are carried and which is installed on the bed; a spindle for retaining a tool, and, with its axis disposed horizontally, provided to rotatable centered on the axis; and a feed mechanism for moving the table and the main spindle relatively to each other along three orthogonal axes.  
         [0003]     2. Description of the Related Art  
         [0004]     Such machine tools known to date include the example illustrated in  FIG. 5  and  FIG. 6  (cf. Japanese Unexamined Pat. App. Pub. No. 2003-266257).  
         [0005]     This machine tool  100  comprises: a bed  101 ; a table  102  for carrying a workpiece W and installed on the upper surface of the bed  101  along the front, movable back and forth (along the Z-axis); a column  103  stood on the upper surface of the bed  101  along the rear; a saddle  104  supported on a front face of the column  103 , movable perpendicularly (along the Y-axis); a spindle head  105  supported on a front face of the saddle  104 , transverse movable sideways (along the X-axis); a main spindle  106  for retaining a tool (not illustrated), and by the spindle head  105  being supported to be rotatable about the spindle axis, which is parallel to the Z axis; a Z-axis guide mechanism  110  for guiding Z-axis directed movement of the table  102 ; a Y-axis guide mechanism  111  for guiding Y-axis directed movement of the saddle  104 ; an X-axis guide mechanism  112  for guiding X-axis directed movement of the spindle head  105 ; a Z-axis feed mechanism  113  for moving the table  102  along the Z-axis; a Y-axis feed mechanism  114  for moving the saddle  104  along the Y-axis; and an X-axis feed mechanism  115  for moving the spindle head  105  along the X-axis.  
         [0006]     Thus, by the table  102 , the saddle  104 , and the spindle head  105  being driven by the respective feed mechanisms  113 ,  114 , and  115  and guided by the guide mechanisms  110 ,  111 , and  112  to travel along the Z-axis, along the Y-axis, and along the X-axis, respectively, the workpiece W on the table  102  and the (not-illustrated) tool on the main spindle  106  are moved relative to each other along the three orthogonal axes directions to machine the workpiece W.  
         [0007]     However, a problem with the conventional machine tool  100  has been that with the saddle  104  being supported on the front face of the column  103  and the spindle head  105  being supported on the front face of the saddle  104 , the saddle  104  and spindle head  105  jut out toward the front face of the machine tool  100 , on account of which deflection or similar deformation occurs in the column  103 , the saddle  104 , and the spindle head  105 , which is prohibitive of precision-machining the workpiece W precisely.  
         [0008]     Furthermore, the Z-axis guide mechanism  110  and the Z-axis feed mechanism  113  are provided on the top face of the bed  101 , the Y-axis guide mechanism  111  and the Y-axis feed mechanism  114  on the front face of the column  103 , and the X-axis guide mechanism  112  and the X-axis feed mechanism  115  on the front face of the saddle  104 . In other words, the Z-axis guide mechanism  110 , the Z-axis feed mechanism  113 , the Y-axis guide mechanism  111 , the Y-axis feed mechanism  114 , the X-axis guide mechanism  112 , and the X-axis feed mechanism  115  are arranged facing the work area where the workpiece W is machined. Consequently, even though the Z-axis guide mechanism  110 , the Z-axis feed mechanism  113 , the Y-axis guide mechanism  111 , the Y-axis feed mechanism  114 , the X-axis guide mechanism  112 , and the X-axis feed mechanism  115  are covered with suitable covers (not illustrated), chips generated during the machining of the workpiece W are likely to intrude into the covers such that maintenance on the covers has to be performed frequently, or expensive covers of complex structure have to be employed.  
         [0009]     Furthermore, with the column  103  being situated along the rear portion of the bed  101 , the Y-axis guide mechanism  111 , the Y-axis feed mechanism  114 , the X-axis guide mechanism  112 , and the X-axis feed mechanism  115  are situated on the rear portion of the bed  101 , a consequent problem has been that performing maintenance on the Y-axis guide mechanism  111 , the Y-axis feed mechanism  114 , the X-axis guide mechanism  112  and the X-axis feed mechanism  115  is difficult.  
         [0010]     In addition, the machine tool  100  typically comprises a tool changer made up of a tool magazine for accommodating a plurality of tools, and an exchange mechanism, among other components. The exchange mechanism is provided at one end with an exchange arm having a grabber for grasping a tool housed in the tool magazine, and at the other end with a grabber for grasping the tool retained by the spindle  106 , whereby the tool in the tool magazine and the tool retained by the spindle  106  can be exchanged by rotating the exchange arm about its rotational center axis paralleling the Z axis and meanwhile moving it along the Z-axis. However, if the installation footprint for the machine tool  100  is restricted widthwise (along the X-axis), the tool magazine and the exchange mechanism cannot be disposed on the lateral flanks of the bed  101 , which leads to the tool magazine and exchange mechanism being disposed on the upper surface of the column  103 . A problem with this situation has been that while the tool magazine and the exchange mechanism, jutting out toward the tip of the spindle  106 , have to be supported by suitable support members, because the tip of the spindle  106  and the column  103  are separated in the Z-axis direction the support structure is destabilized.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     It is an object of the present invention, brought about taking the above-described circumstances into consideration, to provide a machine tool making it possible to perform precisionmachining, perform the maintenance easily, cut down on the cost of manufacturing, and support the tool changer stably. In order to achieve the above object, the present invention provides a machine tool comprising: a bed including a base portion and two side walls standing on both sides of the base portion and opposed to each other with a distance therebetween; a first saddle formed of a rectangular frame member having vertical sides located in parallel with a perpendicular first axis and transverse sides located in parallel with a horizontal second axis, both end portions of which in the horizontal direction being supported on rear faces of the side walls of the bed so as to be movable in the direction of the first axis; a second saddle having an upper portion and a lower portion supported by the first saddle and located movable in the direction of the second axis; a spindle head located within the first saddle and supported by the second saddle such that the spindle head is movable in a direction of a third axis that is perpendicular to the first axis and second axis; a spindle for retaining a tool having an axis line in parallel with the third axis and supported by the spindle head rotatable around the axis line; a table located on the bed for placing a work thereon; a first guide mechanism for guiding the travel of the first saddle in the direction of the first axis; a second guide mechanism for guiding the travel of the second saddle in the direction of the second axis; a third guide mechanism for guiding the travel of the spindle head in the direction of the third axis; a first feed mechanism for moving the first saddle in the direction of the first axis; a second feed mechanism for moving the second saddle in the direction of the second axis; a third feed mechanism for moving the spindle head in the direction of the third axis; and a rotary drive mechanism for rotating the spindle around the axis line.  
         [0012]     According to this invention, since the first saddle is formed of a rectangular frame member in which the spindle head is located, i.e., structures for supporting the saddle and the spindle head that protrude toward front face are omitted unlike the conventional machine tools, it is possible to prevent the bed, the first saddle, the second saddle, and the spindle head from being deformed (deflexed), thereby highly precisely processing works.  
         [0013]     Furthermore, since the first saddle is supported by the rear faces of the side walls of the bed, it is possible to prevent the first guide mechanism and first feed mechanism from facing the work area where works are processed, and to separate the second guide mechanism, the second feed mechanism, the third guide mechanism and the third feed mechanism from the work area. Consequently, it is unlikely that chips would intrude into the first guide mechanism, the first feed mechanism, the second guide mechanism, the second feed mechanism, the third guide mechanism, and the third feed mechanism. As a result, it is possible to simplify the structures of the covers that prevent the chips from intruding into the chip, thereby cutting down on the cost of manufacturing and making it easy to maintain the cover.  
         [0014]     Furthermore, since the first saddle is supported on the rear faces of the side walls of the bed, it is possible to maintain the first guide mechanism, the first feed mechanism, the second guide mechanism, the second feed mechanism, the third guide mechanism, and the third feed mechanism from the rear side of the machine tool, thereby making it easy to maintain the first guide mechanism, the first feed mechanism, the second guide mechanism, the second feed mechanism, the third guide mechanism, and the third feed mechanism.  
         [0015]     Furthermore, since the spindle head has the rear portion to which various pipe arrangements and the wirings are connected, the pipe arrangements and the wirings oppose the movement of the spindle head so that the rear portion of the spindle head is swung and the axis line of the spindle is inclined when the spindle head is moved, thereby deteriorating the machining accuracy. However, according to the invention, since the first saddle is supported on the rear faces of the side walls of the bed, distances between the support portions (a portion of the side walls for supporting the first saddle, a portion of the first saddle for supporting the second saddle, and a portion of the second saddle for supporting the spindle head) and the connection portions of the spindle head with the pipe arrangements and the wirings can be shorter than those in a case that the first saddle is supported on the front faces of the side walls of the bed, so that the rear portion of the spindle head is unlikely to swing around the support portions as fulcrums when the spindle head is moved, i.e., the axis line of the spindle is unlikely to be inclined. This makes it possible to process works precisely, too.  
         [0016]     The machine tool may further comprise a tool changer including a tool magazine accommodating a plurality of tools and an exchange mechanism for exchanging a tool accommodated in the tool magazine with a tool retained by the spindle. The bed may be formed with a support beam bridged across upper portions of the side walls. The tool magazine may be supported on an upper portion of the support beam, and the exchange mechanism may be supported on a lower portion of the support beam.  
         [0017]     Accordingly, since the first saddle is supported on the rear faces of the side walls of the bed, the tip of the spindle and the front face of the support beam can be brought close to each other in a back and forth direction. As a result, the support beam can have structures that stably support the tool magazine and the exchange mechanism, because the tool magazine and the exchange mechanism are not supported protruding toward the tip of the spindle as in the conventional machine tool.  
         [0018]     Furthermore, since the tool magazine is supported on the upper portion of the support beam and the exchange mechanism is supported on the lower portion of the support beam, it is possible to bring the exchange mechanism close to the spindle (to bring the operating region at the tool exchange operation by the exchange mechanism close to the spindle). As a result, it is possible to make preferable the support structures and the positioning relationship of the tool magazine and the exchange mechanism by making the structure of the exchange mechanism compact and shortening the operating time for the tool exchange, for example. In addition, the support beam can strengthen the stiffness of the bed, thereby performing a more precise process.  
         [0019]     As described above, according to a machine tool of the present invention, since the spindle head is located within the frame of the first saddle, the bed, the first saddle, the second saddle, and the spindle head are unlikely to be deformed (deflexed), thereby performing a highly precise process. In addition, since the first saddle is supported on the rear faces of the side walls of the bed, the chips are unlikely to intrude into the first guide mechanism, the first feed mechanism, the second guide mechanism, the second feed mechanism, the third guide mechanism, and the third feed mechanism. As a result, it is possible to simplify the cover structures for preventing the chip intrusion, thereby cutting down on the cost of manufacturing and making it easy to maintain the cover. It is also possible to maintain the first guide mechanism, the first feed mechanism, the second guide mechanism, the second feed mechanism, the third guide mechanism, and the third feed mechanism from the rear side of the machine tool easily. Furthermore, distances between the support portions (a portion of the side walls for supporting the first saddle, a portion of the first saddle for supporting the second saddle, a portion of the second saddle for supporting the spindle head) and the connection portions of the spindle head with the pipe arrangements and the wirings are set shorter, thereby preventing the spindle head from being swung.  
         [0020]     Furthermore, since the first saddle is supported on the rear faces of side walls of the bed, it is possible to bring the tip of the spindle close to the front face of the support beam in a back and forth direction. As a result, the tool magazine and the exchange mechanism can be stably supported by the support beam. Furthermore, since the tool magazine is supported on the upper portion of the support beam and the exchange mechanism is supported on the lower portion of the support beam and the distance between the exchange mechanism and the spindle becomes shorter, it is possible to make preferable the support structures and the positioning relationship of the tool magazine and the exchange mechanism by making the structure of the exchange mechanism compact and shortening the operating time for the tool exchange. Furthermore, since the support beam is bridged over the side walls of the bed, the stiffness of the bed is increased, thereby performing a more precise process.  
         [0021]     From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0022]      FIG. 1  is a perspective view of representing a schematic structure of the machine tool according to one embodiment of the present invention.  
         [0023]      FIG. 2  is a perspective view of the machine tool of  FIG. 1  seen from the rear side.  
         [0024]      FIG. 3  is a cross-sectional view taken along A-A of  FIG. 1 .  
         [0025]      FIG. 4  is a rear view of representing schematic structures of the first saddle, the second saddle, and the spindle head according to another embodiment of the present invention.  
         [0026]      FIG. 5  is a side view of representing a schematic structure of a machine tool according to a conventional example.  
         [0027]      FIG. 6  is a cross-sectional view taken along B-B of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     A description will be made on an embodiment of the present invention with reference to the accompanying drawings.  
         [0029]     As shown in  FIG. 1  through  FIG. 3 , a machine tool  1  in this embodiment comprises a bed  11 , a first saddle  16  placed on the bed  11  so as to be movable in a vertical direction (in the direction of the Y-axis), a second saddle  17  placed on the first saddle  16  so as to be movable in a transverse direction (the X-axis direction) in a horizontal plane, a spindle head  18  placed on the second saddle  17  so as to be movable in a back and forth direction (in the direction of the Z-axis) in a horizontal plane, a spindle  19  for retaining a tool T that is supported by the spindle head  18  so as to be rotatable around the axis line, a table  20  placed on the bed  11  so as to be rotatable around a rotational center line parallel with the Y axis, e.g., around a rotational center line perpendicular to the top face (around B axis), and a tool changer  30  for exchanging the tool T retained by the spindle  19  with a new tool T.  
         [0030]     The machine tool  1  further comprises a Y-axis guide mechanism  21  to guide the travel of the first saddle  16  along the Y axis, an X-axis guide mechanism  22  to guide the travel of the second saddle  17  along the X axis, a Z-axis guide mechanism (not illustrated) to guide the travel of the spindle head  18  along the Z axis, a Y-axis feed mechanism  24  to move the first saddle  16  in the direction of the Y-axis, an X-axis feed mechanism  25  to move the second saddle  17  in the direction of the X-axis, a Z-axis Z-axis feed mechanism  26  to move the spindle head  18  in the direction of the Z-axis, a spindle rotary drive mechanism (not illustrated) to rotate the spindle  19  around its axis line, and a table rotary drive mechanism (not illustrated) to rotate the table  20  in the direction around the B axis to index it to a predetermined position in turning angle.  
         [0031]     The bed  11  consists of a base portion  12 , two side walls  13  that stand on both side of the base portion  12  in the direction of the X-axis and in the center in the direction of the Z-axis and are opposed to each other keeping a distance therebetween, a support beam  14  bridged between upper portions of the side walls  13 . The base portion  12  is formed with a chip discharge hole  12   a  having one end opening on the top face in the center and the other end opening on the rear face, and the top surface of the base portion  12  is formed to be inclined toward the opening at one end of the chip discharge hole  12   a.    
         [0032]     In the chip discharge hole  12   a  is located a chip recovery device  40 , which consists of a discharge mechanism  41  to transport chips generated during the process in a predetermined transfer direction and discharge them out of the machine, a reservoir  42  located upstream in the transport direction and below the discharge mechanism  41  to reserve the cutting fluid, and a recovery box  43  located at the end downstream in the transfer direction and below the discharge mechanism  41 .  
         [0033]     The discharge mechanism  41  is made up of a transport belt and so on, and transfers chips dropped onto the transport belt from the opening of the chip discharge hole  12   a  at one end downstream in the transfer direction (out of the machine). The reservoir  42  reserves the cutting fluid that is dropped with the chips from the opening of the chip discharge hole  12   a  at one end and flown from the discharge mechanism  41 . The recovery box  43  collects the chips dropped off from the discharge mechanism  41  at the end downstream in the transfer direction of the discharge mechanism  41 .  
         [0034]     The first saddle  16  is rectangular and has a shape of frame in which transverse sides are placed in parallel with the X axis and vertical sides are placed in parallel with the Y axis. The first saddle  16  has front faces of the end portions (front faces of the vertical sides) in the direction of the X-axis that are supported on rear faces of the side walls  13  of the bed  11 , and is movable in the direction of the Y-axis.  
         [0035]     The second saddle  17  consists of a flat support portion  17   a , and a tubular container  17   b  located on and protruding from both faces in the center (the front face and the rear face) of the support portion  17   a  and having a through hole  17   c  penetrating therethrough in the direction of the Z-axis. The front face of the upper portion and the front face of the lower portion of the support portion  17   a  are supported by rear faces on the transverse sides of the first saddle  16 , and movable in the direction of the X-axis, while the container  17   b  being located within the first saddle  16 .  
         [0036]     The spindle head  18  is supported in the through hole  17   c  of the container  17   b  of the second saddle  17  so as to be movable in the direction of the Z-axis. The spindle  19  is located such that its axis line is in parallel with the Z axis, and is supported on the front end of the spindle head  18  so as to be rotatable so that it is movable in the directions of the X-axis, the Y-axis, and the Z-axis (the orthogonal three axis directions) within a region surrounded by the base portion  12  of the bed  11 , the side walls  13 , and the support beam  14 .  
         [0037]     Between the rear faces of the side walls  13  and the table  20  in the direction of the Z-axis within the region surrounded by the base portion  12 , the side walls  13 , and the support beam  14 , a cover (not illustrated) is provided to partition the work area where the workpiece W is processed. The cover prevents the chips and the cutting fluid from intruding into the rear portion side (the first saddle  16 , the second saddle  17 , the spindle head  18 , the Y-axis guide mechanism  21 , the X-axis guide mechanism  22 , the Z-axis guide mechanism (not illustrated), the Y-axis feed mechanism  24 , the X-axis feed mechanism  25 , and the Z-axis Z-axis feed mechanism  26 ). The front end of the spindle  19  protrudes beyond the front face of the cover (not illustrated).  
         [0038]     The table  20  is located on a top face near the front face of the base portion  12  of the bed  11  and in the center in the direction of the X-axis, and has a top face on which the workpiece W is placed.  
         [0039]     The Y-axis guide mechanism  21  consists of guide rails  21   a  located on the rear faces of the side walls  13  of the bed  11  along the Y axis, and sliders  21   b  fixed to the front faces of the vertical sides of the first saddle  16  and engaged with the guide rails  21   a  movably.  
         [0040]     The Y-axis feed mechanism  24  consists of drive motors  24   a  that are located on top faces of the side walls  13  of the bed  11 , ball screws  24   b  that are located on the rear faces of the side walls  13  of the bed  11  along the Y axis to be driven by the drive motors  24   a  around the axis centers, and nuts  24   c  that are fixed to the first saddle  16  and screwed with the ball screws  24   b.    
         [0041]     In the Y-axis guide mechanism  21  and the Y-axis feed mechanism  24 , when the drive motors  24   a  are driven to rotate the ball screws  24   b  around the axis centers, the nuts  24   c  move along the ball screws  24   b . Consequently, the first saddle  16  is guided by the guide rails  21   a  and the sliders  21   b  in the direction of the Y-axis.  
         [0042]     The X-axis guide mechanism  22  consists of guide rails  22   a  located on rear face of the first saddle  16  on a transverse side along the X axis, and sliders  22   b  fixed to a front face of an upper portion and a front face of a lower portion of the support portion  17   a  of the second saddle  17  and engaged with the guide rails  22   a  movably.  
         [0043]     The X-axis feed mechanism  25  consists of drive motors  25   a  that are located on traversal sides of the first saddle  16 , ball screws  25   b  that are located on transverse sides of the first saddle  16  along the X axis and rotated by the drive motors  25   a  around the axis centers, and nuts  25   c  that are fixed to the second saddle  17  and engaged with the ball screws  25   b.    
         [0044]     In the X-axis guide mechanism  22  and the X-axis feed mechanism  25 , when the drive motors  25   a  are driven to rotate the ball screws  25   b  around the axis centers, the nuts  25   c  are moved along the ball screws  25   b . Consequently, the second saddle  17  is guided by the guide rails  22   a  and the sliders  22   b  in the direction of the X-axis.  
         [0045]     The Z-axis guide mechanism (not illustrated) consists a guide rail (not illustrated) is located on the inner circumferential surface of the through hole  17   c  of the second saddle  17  along the Z axis, and a slider (not illustrated) fixed to the outer circumferential surface of the spindle head  18  and engaged with the guide rail (not illustrated) movably.  
         [0046]     The Z-axis feed mechanism  26  consists of a drive motor  26   a  located on a rear face of the container  17   b  of the second saddle  17 , a ball screw (not illustrated) located on the second saddle  17  along the Z axis and rotated by the drive motor  26   a  around the axis center, and a nut (not illustrated) fixed to the outer circumferential surface of the spindle head  18  and screwed with the ball screw (not illustrated).  
         [0047]     In the Z-axis guide mechanism (not illustrated) and the Z-axis feed mechanism  26 , when the drive motor  26   a  is driven to rotate the ball screw (not illustrated) around the axis center, the nut (not illustrated) is moved along the ball screw. Consequently, the spindle head  18  is guided by the guide rail (not illustrated) and the slider (not illustrated) in the direction of the Z-axis.  
         [0048]     The tool changer  30  comprises a tool magazine  31  consisting of a magazine main body  32  supported on the top face of the support beam  14  of the bed  11  to accommodate a plurality of tools T therein and a transfer mechanism  36  located on the front face of the support beam  14  to transfer the tool T stored in the magazine main body  32  to the predetermined exchange position and position it there, and an exchange mechanism  37  supported on the top face of the support beam  14  to exchange the tool T retained by the spindle  19  with the tool transferred to the exchange position and positioned there by the transfer mechanism  36 .  
         [0049]     The magazine main body  32  consists of a plurality of retaining members  33  for retaining the tools T, a move mechanism  34  that supports the retaining members  33  to rotate the retaining members  33  that retains the tool T as a thing to be exchanged around a rotational center axis in parallel with the Z axis to the predetermined transfer position, and a support member  35  fixed to the top face of the support beam  14  to support the move mechanism  34 .  
         [0050]     The transfer mechanism  36  transfers the retaining member  33  (tool T), which has been moved to the transfer position by the move mechanism  34  of the magazine main body  32 , downward to position it in the exchange position.  
         [0051]     The exchange mechanism  37  consists of an exchange arm  38  located in parallel with the XY-plane and having a gripper gripping the tool T retained by the spindle  19  at one end and a gripper gripping the tool T transferred and positioned at the exchange position by the transfer mechanism  36  at the other end, and a drive mechanism  39  that supports the exchange arm  38 . The drive mechanism  39  rotates the exchange arm around the rotational center axis in parallel with the Z axis and moves it linearly in the direction of the Z-axis. The drive mechanism  39  is located on the under face of the support beam  14 .  
         [0052]     In the tool changer  30 , first, the retaining member  33  retaining the tool T as a thing to be exchanged is moved by the move mechanism  34  of the magazine main body  32  to the predetermined transfer position, and then is transferred by the transfer mechanism  36  to the exchange position and positioned there. After that, the drive mechanism  38  of the exchange mechanism  39  performs the rotational movement operation and the linear movement operation of the exchange arm  38  to exchange the tool T in the retaining member  33 , which has been moved to the exchange position and positioned there, with the tool T on the spindle  19 .  
         [0053]     According to the machine tool  1  of the embodiment configured as described, the Y-axis feed mechanism  24  moves the first saddle  16  under guide of the Y-axis guide mechanism  21  in the direction of the Y-axis, the X-axis feed mechanism  25  moves the second saddle  17  under guide of the X-axis guide mechanism  22  in the direction of the X-axis, the Z-axis feed mechanism  26  moves the spindle head  18  under guide of the Z-axis guide mechanism (not illustrated) in the direction of the Z-axis, and the spindle rotary drive mechanism (not illustrated) rotates the spindle  19  around the center axis line. As a result, the workpiece W on the table  20  is processed by the tool T retained by the spindle  19 .  
         [0054]     The chips generated in the cutting process and the cutting fluid supplied into the contact portion between the tool T and the workpiece W are dropped off from the chip discharge hole  12   a  of the base portion  12  onto the discharge mechanism  41 . The chips are transferred by the discharge mechanism  41  and collected into the recovery box  43 . The cutting fluid is flown downward from the discharge mechanism  41  and is collected into the reservoir  42 .  
         [0055]     During the process, the table  20  (the workpiece W on the table  20 ) is indexed by the table rotary drive mechanism (not illustrated) to the predetermined position in turning angle in the direction around the B axis. The tool T retained by the spindle  19  can be exchanged by the tool changer  30  with various tools T stored in the tool magazine  31  as necessary.  
         [0056]     As described above, in the machine tool  1  of the embodiment, since the first saddle  16  is rectangular and has a shape of frame in which the second saddle  17  is located, and the second saddle  17  is formed with the through hole  17   c  into which the spindle head  18  is located, omitting structures for supporting the saddle  104  and the spindle head  105  protruding toward the front face in the conventional machine tool  100 , it is possible to prevent the bed  11 , the first saddle  16 , the second saddle  17 , and the spindle head  18  from being deformed (deflexed, for example), thereby highly precisely processing the workpiece W.  
         [0057]     Furthermore, since the first saddle  16  are supported on the rear faces of the side walls  13 , it is possible to prevent the Y-axis guide mechanism  21  and the Y-axis feed mechanism  24  from facing the work area. It is also possible to separate the X-axis guide mechanism  22 , the X-axis feed mechanism  25 , the Z-axis guide mechanism (not illustrated), and the Z-axis feed mechanism  26  from the work area. Consequently, it is unlikely that the chips intrude into the Y-axis guide mechanism  21 , the Y-axis feed mechanism  24 , the X-axis guide mechanism  22 , the X-axis feed mechanism  25 , the Z-axis guide mechanism (not illustrated), and the Z-axis feed mechanism  26 . As a result, it is possible to simplify a structure of the cover (not illustrated), thereby cutting down on costs of manufacturing and making it easy to maintain the cover (not illustrated).  
         [0058]     Furthermore, since the first saddle  16  is supported on the rear faces of the side walls  13 , it is possible to carry out maintenance of the Y-axis guide mechanism  21 , the Y-axis feed mechanism  24 , the X-axis guide mechanism  22 , the X-axis feed mechanism  25 , the Z-axis guide mechanism (not illustrated), and the Z-axis feed mechanism  26  from the rear side of the machine tool  1 . In other words, it is possible to make it easy to maintain the Y-axis guide mechanism  21 , the Y-axis feed mechanism  24 , the X-axis guide mechanism  22 , the X-axis feed mechanism  25 , the Z-axis guide mechanism (not illustrated), and the Z-axis feed mechanism  26 .  
         [0059]     Since various pipe arrangements and wirings are connected with the rear portion of the spindle head  18 , when the spindle head  18  is moved, the pipe arrangements and wirings oppose the movement so that the rear portion of the spindle head  18  is swung and the axis line of the spindle  19  is inclined, thereby deteriorating the machining accuracy. However, since the first saddle  16  is supported on the rear faces of the side walls  13 , distances between the support portions (a portion of the side walls  13  for supporting the first saddle  16 , a portion of the first saddle  16  for supporting the second saddle  17 , and a portion of the second saddle  17  for supporting the spindle head  18 ) and the connection portions of the spindle head  18  with the pipe arrangements and the wirings can be shorter than those in the case that the first saddle  16  is supported on the front faces of the side walls  13 . Consequently, when the spindle head  18  is moved, the rear portion side of the spindle head  18  is unlikely to swing around the support portions as fulcrums, i.e., the axis line of the spindle  19  is unlikely to be inclined. As a result, this makes it possible to precisely process the work, too.  
         [0060]     Furthermore, since the first saddle  16  is supported on the rear faces of the side walls  13 , the tip of the spindle  19  and the front face of the support beam  14  can be located close to each other in the direction of the Z-axis. Consequently, the tool magazine and the exchange mechanism are not supported protruding toward the tip of the spindle  106 , unlike the conventional machine tool  100 . As a result, it is possible to stabilize the structure of the support beam  14  for supporting the magazine main body  32 , the transfer mechanism  36 , and the exchange mechanism  37 .  
         [0061]     Furthermore, since the magazine main body  32  is placed on the top face of the support beam  14 , the transfer mechanism  36  is placed on the front face of the support beam  14 , and the exchange mechanism  37  is placed on the under face of the support beam  14 , it is possible to bring the exchange mechanism  37  close to the spindle  19  (to bring the operating range of the exchange arm  38  at the tool exchange operation close to the spindle  19 ), it is possible make preferable the support structures and the positioning relationships of the magazine main body  32 , the transfer mechanism  36 , and the exchange mechanism  37 , e.g., making the exchange arm  38  compact or shortening the operating time for the tool exchange. It is also possible to perform a more highly precise process because the support beam  14  improves the stiffness of the bed  11 .  
         [0062]     Although the one embodiment of the present invention is described above, specific embodiments that can be employed by the present invention are not limited to this embodiment.  
         [0063]     For example, the structures of the tool magazine  31  (the magazine main body  32  and the transfer mechanism  36 ) and the exchange mechanism  37  of the tool changer  30  are not limited those described above, and various structures can be employed.  
         [0064]     The base portion  12 , the side walls  13  and the support beam  14  of the bed  11  may be formed integrally or may be formed of separate members.  
         [0065]     The structure of the Z-axis guide mechanism (not illustrated) is not specifically limited as in the above embodiment. In one example, a guide rail (not illustrated) may provided on inner circumferential surface of the lower portion of the through hole  17   c , and a slider (not illustrated) may be provided on the outer circumferential surface of the lower portion of the spindle head  18 . In another example, a guide rail (not illustrated) may be provided on the inner circumferential surface of the upper portion of the through hole  17   c , and a slider (not illustrated) may be provided on the outer circumferential surface of the upper portion of the spindle head  18 . In a further other example, guide rails (not illustrated) may be provided on the inner circumferential surface of the upper portion and the inner circumferential surface of the lower portion of the through hole  17   c , and sliders (not illustrated) may be provided on outer circumferential surface of the upper portion and the outer circumferential surface of the lower portion of the spindle head  18 . In a further other example, guide rails (not illustrated) are provided on left and right sides of the inner circumferential surfaces of the through hole  17   c , sliders (not illustrated) may be provided on the left and right sides of the outer circumferential surface of the spindle head  18 . In a further other example, a guide rail (not illustrated) may be provided on the outer circumferential surface of the spindle head  18 , and a slider (not illustrated) may be provided on the inner circumferential surface of the through hole  17   c , as in the cases described above.  
         [0066]     Furthermore, although the second saddle  17  is formed with the container  17   b  and the through hole  17   c , in which the spindle head  18  is placed in the above example, the present invention is not limited to this example. For example, as shown in  FIG. 4 , a second saddle  50  may be formed of a U-shaped support portion  50   a  and a container  50   b  having an opening upper portion, which supports the spindle head  18 . It should be noted that the Y-axis feed mechanism  24 , the X-axis feed mechanism  25  and the Z-axis feed mechanism  26  are omitted in  FIG. 4 .  
         [0067]     In this case, the support portion  50   a  is formed flat, and the container  50   b  is formed such that it protrudes from the front face and rear face of the support portion  50   a  in the direction of the Z-axis, and the spindle head  18  is supported by the container  50   b  so as to be positioned within the frame of the first saddle  16 . In addition, the Z-axis guide mechanism  51  that guides the travel of the spindle head  18  in the direction of the Z-axis consists of guide rails  51   a  that are located on the top face of the bottom portion of the container  50   b  of the second saddle  50  along the Z axis and sliders  51   b  that are fixed to the outer circumferential under face of the spindle head  18  and engaged with the guide rails  51   a  movably. It should be noted that the guide rails  51   a  may be provided on inner circumferential surfaces of the side walls of the container  50   b , and the sliders  51   b  may be provided on left and right sides of the outer circumferential surface of the spindle head  18 . Alternatively, the guide rails  51   a  may be provided on the spindle head  18 , and the sliders  51   b  may be provided on the container  50   b.    
         [0068]     Only selected embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.