Abstract:
A machine tool for machining gear teeth into an inner side of an annular workpiece, the tool comprising a circular substructure having an upper side, a rotary bearing on which is disposed an annular machining table adapted to support a workpiece, a chassis for supporting a tool head, and a plurality of exchangeable machining rings, an adaption ring supporting the machining ring and supporting concentric cones, and a braking device adapted to act on the adaption ring.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention is directed to a machine tool for incorporating gear teeth into the inner side of an annular workpiece, preferably by machining (or: metal cutting). 
     (2) Description of the Prior Art 
     The production of gear teeth on the inner side of annular objects is somewhat more difficult than the incorporation of external teeth on gear wheels or the like. In particular, various methods involving the use of a worm milling cutter for hobbing the surface to be provided with gear teeth are not possible. Rather, machining processes that are considered suitable for internal gear teeth are shaping or—in particular in the case of machining large rings—milling of the teeth by means of a milling cutter. In this case, the workpiece to be machined, still without teeth, is placed onto a table, for example in the form of a circular disk, and fixed there. The machine head is held over the inner space within the ring to be machined by means of an extension arm from a stand arranged alongside the table. By driving the machining tool—rotation of a milling head or reciprocating movement in the case of a shaping machine—one tooth after the other is incorporated, the table being turned further by an amount corresponding to the spacing between the teeth after the completion of a tooth. In the case of this procedure, the extension arm carrying the machining head represents a weak point, because the high cutting forces originating from the machining head can only be insufficiently absorbed by this extension arm and vibration of the arrangement is therefore unavoidable. Such vibration is extremely undesirable, however, because it results in inaccurate cuts. 
     SUMMARY OF THE INVENTION 
     These disadvantages of the prior art described result in the problem initiating the invention, that of developing a machine tool of the generic type in such a way that the machining forces occurring during a properly performed operation, in particular cutting forces, cannot make the machine vibrate. 
     The solution to this problem is achieved by an annular machining table for placing on or supporting a workpiece, in particular placed flat, and a chassis for holding, supporting, mounting and/or guiding a tool head, at least during the machining, which chassis extends through the annular machining table or through a central opening in the annular machining table from a machine bed (or: bed) or pedestal below the machining table of the machine. 
     The fact that the machining head is connected in such a way to the machine bed or pedestal by the shortest route, that is through a central opening in the machine table, allows even higher machining forces, in particular cutting forces, to be diverted without any problem into the bed or pedestal of the machine, without any appreciable vibrations being induced as a result. This is so since, by contrast with a freely projecting extension arm as in the prior art, the chassis according to the invention of the machining head can be formed so as to be extremely solid, and consequently extremely rigid. 
     It has proven to be favorable that the machining table is mounted rotatably about a vertical axis of symmetry. This avoids rotation of the chassis together with the machining head, which further increases the accuracy with which it is guided. On the other hand, the annular tool table can for its part be mounted extremely precisely, so that a workpiece fixed on it concentrically in relation to the axis of rotation does not undergo any radial offset during its rotation and the machining can therefore be performed with extremely high precision. 
     In an advantageous embodiment it is envisaged to mount the machining table on the upper side of a substructure, preferably approximately in the form of a lateral surface. In simple terms, this substructure (or: lateral surface or substructure in the form of a lateral surface) preferably offers sufficient space in its interior for the machining head together with the carrying chassis thereof and, possibly, a carriage supporting the two. The substructure may also have large-area clearances, on the one hand as access to the interior, but on the other hand also to allow the machining head, chassis, etc. to be adjusted or moved, possibly even within wide limits. In order for such an interruption in the substructure not to overly weaken its stability, the height of such clearances is preferably chosen to be smaller than the height of the substructure in the form of a lateral surface, so that a web defining the circumference of the substructure still remains above and/or below the clearance. 
     In a way corresponding to the table to be supported, for instance in the form of a circular ring, its substructure may have in the region of its upper side a clearance, preferably with a cross section in the form of a circular ring, in particular with a clear diameter corresponding to the inside diameter of the rotary connection, in order to obtain a maximum path of movement. The substructure is capable of supporting the table along its entire circumference without any gaps, thereby eliminating the possibility of sagging under the weight of one or more workpieces lying on it. 
     It is advantageous if the substructure has at the upper side a cross section in the form of a circular ring and/or a circular outer contour in cross section, and consequently is well adapted in form to the machining table. The cross section is preferably considered in a sectional plane perpendicular to the vertical direction and/or gravitational force or perpendicular to the axis of rotation. 
     On the other hand, the substructure for the machining table may have in the region of its base an approximately or at least almost polygonal, preferably quadrangular or rectangular, in particular approximately square, cross section or an approximately or at least almost polygonal, in particular quadrangular or rectangular, in particular approximately square, outer contour in cross section. 
     The quadrangular or rectangular geometry is advantageously adapted to the fact that the chassis together with the machining head should be displaceable in a radial direction, with respect to the axis of rotation of the machining table, in order to place the machining tool, for example a milling cutter, against a workpiece from the inside. Such a displacement requires a tunnel-like construction with side edges parallel to one another and, preferably, with short guiding rails, approximately of the same length. The same define a quadrangle or are directed orthogonally in relation to one another, so that the two mutually orthogonal directions of displacement and the corresponding guiding elements or guiding rails are preferably aligned along the side edges of the quadrangular or rectangular base of the inner structure and the configuration of the inner space within the substructure is correspondingly adapted. 
     In particular for reasons of optimum statics, with greatest possible flexural rigidity, it is preferred if the cross section of the substructure for the machining table steadily changes between its upper side, on which the machining table is mounted, on the one hand, and its base, which is arranged on or toward the machine bed, on the other hand. In particular, the circular outer contour of the substructure and/or its cross section at the upper side steadily goes over into the quadrangular or rectangular, in particular square, outer contour of the substructure and/or its cross section at its base. 
     This may be achieved in the first embodiment by the lateral surface or the outer surface of the substructure extending approximately vertically in the region of four points of its circular upper edge that are respectively offset by 90° from one another to the underside or base of the substructure, that is to say with a maximum slope or maximum angle of slope φ max  with respect to the horizontal base area of approximately 90°. 
     These regions of the underside or base may respectively form the side midpoints of four edges of a square underside or base of the lateral surface. By contrast, a vertical section through the lateral area along the axis of rotation of the annular area at the upper side on the one hand and through one of the four corners of the square on the other hand has a minimum slope or minimum angle of slope φ min ; this slope or angle of slope lies, for example, between 40° and 80°, in particular between 50° and 70°. Between these eight lines, which are offset with respect to one another by 45° in each case with respect to the axis of rotation of the machining table, the angle of slope φ respectively varies between φ min  and φ max , according to φ min ≦φ&lt;φ max . 
     In other words, the wall or outer area of the substructure extends
         (i) at least almost vertically or at a maximum angle of slope in the region of four outer points on the at least almost circular upper side that are respectively offset by 90° from one another to the base of the substructure, in particular in each case to the side midpoint respectively of one of four edges of the rectangular or square base,   (ii) at at least a minimum angle of slope in the region of four further inner points on the at least almost circular upper side that lie respectively between two of the outer points in the circumferential direction to the base of the substructure, in particular in each case to an associated corner of the rectangular or square base, and   (iii) at varying angles of slope, between the maximum angle of slope and the minimum angle of slope, in the circumferential direction between the outer points and the inner points.       

     The edge length of the square preferably corresponds approximately to the diameter of the upper side in the form of a circular ring. Therefore, in particular, the circle at the upper side of the substructure forms in the projection onto the base an inscribed circle in the square at the base of the substructure, which therefore has the same center point as the square and tangentially touches the side edges of the square at their midpoint. 
     In another, second embodiment, the lateral area or outer area of the substructure may also be made up of four planar and/or vertical wall portions or side walls, which at the base of the substructure or lateral surface meet the edges of the quadrangle or square there, and of four vaulted portions or curved, preferably convexly curved, i.e. outwardly vaulted, intermediate walls that join the four planar and/or vertical wall portions or side walls to one another. The vaulted portions or intermediate walls narrow toward the base and/or end in the form of a point in its corners and/or widen upwardly toward the upper side and/or finally come together in the region of the upper side, or merge with one another, in particular if the side walls, in particular vertical side walls, narrow there to a point of the wall. 
     In particular, from each point of the upper side, and also from each point of the base of the substructure, there extends in each case a straight line, which extends along the lateral surface to the respectively opposite end face of the lateral surface—the underside or the upper side. In this case, all such lines extending from the edges of the square converge upward to the point of the side wall concerned, where they all meet, like the lines running from the base of an (isosceles) triangle to the apex thereof. In turn, all the lines extending from a circumferential region of the upper side that lies between two adjacent points of these four points converge to a corner in each case of the base quadrangle, in a way corresponding to a piece of the lateral area of an (oblique) inverted cone, the apex of which does not lie above or below the base area but laterally outside the same. Accordingly, the lateral area is preferably made up of an alternating succession of upright, preferably isosceles, triangles and, in between in each case, a lateral portion of an inverted, preferably oblique, cone, an edge line of a triangle portion respectively coinciding with an edge line of a cone portion. 
     It is within the scope of the invention that the chassis for holding, supporting, mounting and/or guiding a tool head has a horizontally movable carriage. The carriage track is preferably defined by one or more guiding rails, which is/are anchored on the machine bed or pedestal. If there is only a single rail, it should run through the axis of rotation or through the center point of the base quadrangle; two rails may extend symmetrically on both sides of this center point. This railway is preferably bounded at two end faces, one of which lies within the enclosure in the form of a lateral surface, the other lies outside it. In the region of this or these guiding rail(s), the substructure in the form of a lateral surface is interrupted, so that the carriage can, at least partly, be moved out of the substructure and back. 
     The invention can be developed to the extent that the chassis for holding, supporting, mounting and/or guiding a tool head has a vertically movable carriage. While the horizontally movable carriage serves for adjusting the milling or machining head, the latter is lifted or lowered by means of a vertically movable carriage, in order to produce straight gear teeth with constant tooth cross sections along the axis of rotation. 
     The fact that the vertically movable carriage is guided on the horizontally movable carriage allows the machining head to be adjusted along a vertical plane with predefined limits. In this case, the vertical carriage moves up and down within the clearance in the machining table, while the horizontal carriage is moved on its guiding rails to a greater or lesser extent into the inner space of the substructure in the form of a lateral surface. For this purpose, the horizontal carriage is lower than the substructure, so that it fits under the machining table; the vertical carriage is more slender than the clearance within the machining table, in order that it can move through this clearance. 
     Also provided are retaining devices, in particular brakes, for fixing the horizontally movable carriage during machining. Serving primarily as the machine tool is a milling tool, which is preferably arranged, in particular mounted, on a milling head in the form of a vertically movable carriage. This may preferably be a disk-shaped body with cutting teeth arranged on its circumference, the geometry of which teeth is fixed such that an axial cut by one tooth of the tool corresponds approximately to the cross section of the gap between two adjacent teeth of the internal gear teeth to be milled in. 
     Such a milling tool should be mounted rotatably about a horizontal axis in such a way that the planar base or a main area of the disk-shaped tool body is vertically oriented, preferably approximately radially with respect to the axis of rotation of the machining table. 
     Finally, it corresponds to the teaching of the invention that the axis of rotation of the milling tool, the direction of displacement of the vertically movable carriage and the direction of displacement of the horizontally movable carriage respectively form a right angle to one another, so that the teeth of the rotating tool on the lateral area perform an approximately vertical movement in their region of engagement. This has the advantage that the forces occurring during such a cutting operation are directed approximately vertically and are therefore either absorbed from the workpiece by the horizontal table plate or—with a reversed direction of rotation of the milling cutter—are compensated entirely or largely by the weight of the workpiece to be machined. The workpiece is not displaced thereby because it is firmly clamped, since its weight alone is not sufficient here for fixing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, details, advantages and effects on the basis of the invention emerge from the following description of a preferred embodiment of the invention and with reference to the drawing, in which: 
         FIG. 1  shows a machine tool according to the invention in a perspective view; 
         FIG. 2  shows a plan view of  FIG. 1 ; 
         FIG. 3  shows a section through  FIG. 2  along the line III - III; and 
         FIG. 4  shows an enlarged representation of the detail IV from  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The machine tool  1  rests on a machine bed  2  in the form of a solid base plate, which is anchored, for example firmly screwed, on a concrete pedestal or the like. The machine bed  2  has a square base area, with a continuation  3  adjoining on one side, preferably with a width reduced to approximately 70 to 90% in relation to the edge length of the square portion of the machine bed  2 . The continuation  3  is intended to allow the horizontal movement of a carriage  20  and is therefore dependent in its length on the required path of movement of this carriage  20  in the horizontal direction. 
     Rising up above the square main portion  4  of the machine bed  2  is a substructure  5  in the form of a lateral area for the actual, rotatably arranged machining table  6 . For this purpose, the substructure  5  has an upper side  7  in the form of a circular ring, on which the actual machining table  6 , likewise in the form of a circular ring, rests by means of a rotary bearing  8 . The outside diameter of the upper side  7  corresponds approximately to the outside diameter of the machining table  6 . 
     The base area  9  of the substructure  5  in the form of a lateral area corresponds to the base area of the main portion  4  of the machine bed  2 , so that the substructure can be fixed by means of machine screws passing partially through the machine bed  2 . Provided for this purpose in the lower region of the substructure  5  and in the machine bed  2  are clearances  10 , in which screw heads, nuts or other threaded elements are accessible. The substructure  5  could, however, also be firmly welded on the machine bed  2 . 
     Between its upper side  7  and its base area  9 , the cross section of the substructure  5  goes over steadily and continuously from the approximately cylindrical form at the upper end into the approximately box-shaped form at its lower end. An essential feature here is the approximately constant wall thickness of the order of magnitude of between 10 cm and 40 cm, preferably more than 15 cm, in particular 20 cm or more, depending on the loads to be expected and to be supported on the machining table. In particular in cases of greater wall thicknesses, it is recommendable to make the substructure take the form of two shells arranged one inside the other, with an approximately constant spacing and/or with an intermediate or hollow space possibly narrowing slightly upwardly, into which a preferably hydraulically setting composition, in particular a non-shrinking concrete, is introduced; in cases of smaller wall thicknesses, the substructure  5  could also be of a solid configuration. The substructure  5  should, however, in any event be sufficiently heavy, i.e. of high mass, to be able to dampen the vibrations originating from the machining as optimally as possible. 
     The continuous transition of the substructure  5  from its approximately box-shaped foot region to its approximately cylindrical head region is brought about by the substructure  5  being made up of a total of eight portions. 
     These include a total of four vertical walls  11 , which each rise up over a side edge  12  of the square main portion  4  of the machine bed  2 . Each wall  11  has the area of an isosceles triangle, the base of which corresponds to the edge length of the square main portion  4  of the machine bed  2 , and the height of which corresponds approximately to the overall height of the substructure  5 . 
     On account of the upwardly decreasing width of the walls  11 , upwardly widening gaps are obtained in each case in the corner regions between every two adjacent, planar walls  11 . The edge lines of adjacent walls  11  are joined by in each case a vaulted portion  13 . These vaulted portions  13  respectively follow a portion of the lateral area of an inverted cone, the apex of which does not lie vertically above or below its base area, but protrudes as it were outwardly beyond the same. 
     As already indicated above and evident from  FIG. 3 , between the circular upper side  7  of the substructure  5  and the actual machining table  6  there is a rotary mounting  8 . The details of this rotary mounting  8  are illustrated in  FIG. 4 . 
     It follows from this that a terminating ring  44 , preferably of solid metal, rests on the upper side  7  of the substructure  5  in the form of a circular ring. 
     On it, the inner ring  45  of the rotary bearing  8  is fixed, in particular screwed on by means of a multiplicity of fastening screws arranged in the form of a ring, parallel to the vertical axis of rotation of the rotary mounting  8 . On the outer circumference of the inner ring  45  there is a projection  46  with an approximately rectangular cross section, running around said ring in the form of a collar. This projection  46  is joined along its radially inner side to the inner ring  45 , in particular is produced integrally or formed together with it, for example machined from one and the same ring by corresponding turning on a lathe. The other three sides of the projection  46  respectively form a running area for in each case one of a total of three rows of rolling bodies  47 ,  48 ,  49 . The rolling bodies  47 ,  48 ,  49  are preferably in each case rollers, in particular cylindrical rollers. 
     The outer ring  50  of the rotary mounting  8  is subdivided into two separately produced rings  51 ,  52 . After their assembly, the two rings  51 ,  52  are joined together, in particular by means of screws, and then have an approximately C-shaped cross section overall, i.e. they reach on the one hand over the projection  46  of the inner ring  45 , in the region of the upper side of the upper ring  51 , and on the other hand under the projection  46  of the inner ring  45 , in the region of the underside of the lower ring  52 . On each of the sides of the outer ring  50  that are facing the projection  46  there is a runway for the three rows of rolling bodies  47 ,  48 ,  49 . 
     Of these, the rolling bodies  47  of the uppermost row, the axes of rotation of which point approximately radially outward from the axis of rotation of the rotary mounting  8 , primarily bear the weight of the machining table  6  together with workpieces  16  lying on it. 
     The axes of rotation of the rolling bodies  48  of the second or—seen in the vertical direction—middle row are vertically aligned, in the manner of a radial bearing. These rolling bodies  48  undertake the precisely concentric guidance of the machining table  6  with respect to the substructure  5 . 
     The rolling bodies  49  of the third or lowermost row are intended—possibly in interaction with the upper rolling bodies  47 —to absorb tilting moments, and thereby also ensure an exact horizontal position of the machining table  6 , together with workpieces  16  lying on it, at all times during machining. 
     For the rotational driving of the machining table  6 , on the outer ring  50 —preferably on its lower part  52 —there is a preferably radially extended region  53  with external teeth. Meshing with these external teeth is a driven element of at least one drive  54  that is provided with teeth. 
     The (each) drive  54  (each) comprises an electric motor  55 , which is fastened, in particularly screwed, to an outwardly protruding, plate-shaped continuation  56  on the outer circumference of the terminating ring  44  with a horizontal base area. Preferably, this plate-shaped continuation  56  with a horizontal base area is supported by a plate  57  with a vertical base area, for example a polygonal, preferably triangular or quadrangular, in particular trapezoidal, base area. This is made to abut, in particular butt-welded, with one (longitudinal) side  58  on the outer side of the substructure  5 , in particular in the region of a side midpoint of the same, while its upper side extends approximately at right angles thereto, i.e. horizontally, and is in supporting contact with the plate-shaped continuation  56 , preferably is connected, in particular welded or screwed, thereto. 
     In this case, the arrangement is made such that the (each) drive  54  has a vertically upwardly protruding driven shaft  59 , rotationally fixed on which there is a gear wheel  60 , which is in meshing engagement with the external teeth on the radially widened region  53  of the outer ring  50 . By rotationally adjusting this gear wheel  60 , the machining table  6  can be turned. A (reduction) gear mechanism may be connected between the electric motor  55  and the gear wheel  60 , in order to adapt the rotational speed of the electric motor  55  optimally to the desired rotational speed of the machining table  6 ; this may, however, also be brought about by electronic means, for example by activating the electric motor  55  by way of a converter. With such a control device, not only the rotational speed of the electric motor  55  can be controlled, but possibly also its position or rotational position, in order to be able to take the machining table quite specifically to certain rotational positions or machining positions, which is very important for constant distances between the individual teeth of the workpiece  16 . For position control, a position encoder, for example an incremental encoder, resolver or the like, may for example be arranged on the driven shaft  59  of the electric motor  55 . Of course, as an alternative thereto, the rotational position of the machine table  6  itself can also be measured, for example by means of an (incremental) scale adhesively attached or otherwise fixed to the outer or inner side of the outer bearing ring  50 . 
     Resting on the upper side of the outer ring  50  is an adaption ring  61 , which is connected in a rotationally fixed manner to the outer ring  50 , in particular by a series of connecting screws arranged such that they are distributed in the form of a ring. On the outer circumference of the adaption ring  61  there is a disk-shaped extension  62 , which runs between the brake shoes of one or more arresting brakes. The arresting brakes - preferably distributed at equal spacings of, for example, 90° each over the circumference of the machine table  6 —are fixed on the substructure  5 . They may be actuated electrically or hydraulically, in order to connect the machine table  6  immovably to the substructure  5  according to the setting of a desired machining position. Before each rotational adjustment of the machining table  6  by means of the drive/drives  54 , the arresting brakes are released. 
     The adaption ring  61  offers a standardized connection for a workpiece-specific machining ring  63  lying on it. Both rings  61 ,  63  are self-centering, in that they each have conically worked areas  64 ,  65  in the region of their mutual abutting areas. Near the inner side of the adaption ring  61  there is preferably an inner cone  64  and, at a position corresponding thereto of the workpiece-specific machining ring  63 , a complementary outer cone  65 . Furthermore, the adaption ring  61  has in its planar upper side a large number—for example  16 —of fastening bores arranged in the form of a ring, which serve for screwing on a placed-on, workpiece-specific machining ring  63 . 
     Different machining rings  63  are adapted, in particular with regard to their inside diameter—possibly also with regard to their load-bearing capacity or strength—to different workpieces. For connection to one or more workpieces, possibly stacked one above the other, they have on their upper side receptacles  66  for fastening means, for example in the form of threaded rods inserted through connection bores of the workpieces  16 . For this purpose, the receptacles  66  may be provided with an internal thread. 
     Machined in the upper side  14  of the square main portion  4  of the machine bed  2  is a channel-shaped depression  15 . A conveyor belt may, for example, be arranged therein, its task being to transport away chips falling down inside the substructure  2  from the machining of a workpiece  16  by metal cutting. For this purpose, the channel  15  is led out on one side of the machine bed  2 , preferably diametrically opposite the extension plate  3 , to the outside. At this point, the necessary aperture in the substructure is widened in the manner of a passage  17 , which allows a person to enter the inner space of the substructure  5 . 
     In the region of the extension  3  on the square main portion  4  of the machine bed  2 , by contrast, a gate-like opening  18  is provided in the substructure  5 , in order to make it possible for a carriage  20  carrying the machining head  19  to pass through. 
     For guiding this carriage  20 , arranged on the other side of the machine bed  2  are two rails  21 , which are parallel to one another, extend from the main portion  4  of the machine bed  2  to the extension  3  thereof and preferably have an undercut cross section, for example of a dovetailed form. 
     The carriage  20  is guided along these rails  21  by a number of guiding elements on the underside of its approximately rectangular base plate  22 , the cross section of which is designed approximately to complement the cross section of the rails, preferably in such a way that the rails  21  are engaged on their upper side by the guiding elements. 
     For the movement  23  of the carriage  20  in the direction of its guiding rails  21 , extending between the same, between the base plate  2 - 4  and the base plate  22  of the carriage  20 , is a spindle  24 , which is rotatably mounted in at least one bearing  25  of the machine bed  2 , in particular on its extension  3 , and is provided with a connection  26  for the coupling of a motor. Fixed to the underside of the carriage  20 , in particular to the underside of its base plate  22 , is a spindle nut  27 , into which the spindle  24  is screwed. Motor-driven rotation of the spindle  24  has the effect of screwing the spindle nut  27  along the spindle  26 , mounted undisplaceably in the axial direction  25 , and of imparting to the carriage  20  the shift in the direction of the rails  21  that it undergoes thereby. Depending on the direction of rotation of the spindle  26 , the carriage  20  thereby moves either through the door opening  18  in the substructure  5  into the inner space  28  thereof or out from it. This is possible because a vertical section through the carriage  20  transversely to its direction of advancement  23  is smaller than the cross section of the door opening  18 , so that the carriage  20  fits through it without colliding. 
     On the base plate  22  of the carriage  20 , its structure rises up, comprising an upright, front transverse wall  29 , facing the inner space  28 , and a rear supporting structure  30 . The supporting structure  30  is formed by two supporting walls  31 , which extend in the direction of the rails  21  and converge toward one another from the base plate  22  of the carriage  20  to an upper, roof-like connection  32 . To reduce the overall weight, the rear end face  33  of the two supporting walls  31  may be angled, for example at an angle of between 30° and 60° with respect to the vertical. 
     The upright, front transverse wall  29  carries on its front side, facing away from the supporting structure  30 - 33 , two vertical guiding rails, which are parallel to one another and have a rotatably mounted spindle  34  with a vertical longitudinal axis in between. Serving for the motor-driven rotation of the vertical spindle  34  is a drive motor, which is coupled thereto in a rotationally fixed manner and the housing of which may be fixed on the upper side of the base plate  22  of the horizontally movable carriage  20 . 
     A milling head  35  has a rear wall  36 , which is parallel to the transverse wall  29  and has guiding elements assigned to this transverse wall  29  for vertically displaceable guidance with respect to the transverse wall  29 . When the vertical spindle  34  rotates, a spindle nut  26  is screwed up or down on it and transmits its vertical movement  37  to the vertical slide  35 . The milling head  35  is dimensioned such that it is possible to place a circumscribed circle of a diameter much smaller than the diameter of the clearance  41  in the machining table  6 , for example only 0.8 thereof or even smaller, in particular only 0.6 thereof or less, around a horizontal section through the head. This produces an adequate freedom of movement in the horizontal direction, within which neither the substructure  5  nor the machining table  6  hinders the horizontal movement of the machining head  19  in the direction of the rails  21 . 
     The machining head  19  carries a cutting tool for machining by metal cutting the inner side of one or more workpieces  16 , which are preferably identical and possibly chucked one above the other. Preferred here is a milling cutter  39 , which rotates about an axis of rotation  40 , cf. arrow  42 , which is oriented at right angles to the two directions of carriage advancement  23 ,  37 . 
     The preferred production method is the profile milling of individual tooth gaps by means of a side-and-face milling cutter  39 , the cutting edges of which follow a profile corresponding to the tooth gaps to be milled in; preferably, the cutting edges of the side-and-face milling cutter  39  are arranged on the circumference or lateral side thereof and, according to the profile of the gear tooth or tooth gap to be produced, also extend along the transitional regions to the two end faces of the side-and-face milling cutter  39 . With the reciprocating movement  37 , the rotating tool  39  is drawn slowly through the inner side of a workpiece  16 , so that even a number of workpieces  16  arranged in a stack one above the other can be machined in one operation. After completion of one tooth gap, the milling cutter  39  is moved out from the tooth gap just produced, the entire carriage  20  being moved in the horizontal direction  23 ; then, the machining table  6  together with the workpiece(s)  16  is turned further by one tooth spacing in the direction of the arrow  43  and then stopped again. Once the side-and-face milling cutter  39  has been moved by means of the carriage  20  onto the inner side of a workpiece  16  again, the milling operation for the next tooth gap begins with the initiation of the reciprocating movement  37 . 
     However, other production methods would also be conceivable, such as for example hobbing or shaping. In such a case, only the machining head  19  would have to be modified, and possibly the program for the activation and coordination of the various drives. 
     LIST OF DESIGNATIONS 
     
         
           1  machine tool 
           2  machine bed 
           3  extension 
           4  main portion 
           5  substructure 
           6  machining table 
           7  upper side 
           8  bearing 
           9  underside 
           10  clearance 
           11  wall 
           12  side edge 
           13  vaulted portion 
           14  upper side 
           15  channel 
           16  workpiece 
           17  passage 
           18  opening 
           19  machining head 
           20  carriage 
           21  rails 
           22  base plate 
           23  movement 
           24  spindle 
           25  bearing 
           26  connection 
           27  spindle nut 
           28  inner space 
           29  front wall 
           30  supporting structure 
           31  supporting wall 
           32  roof-like connection 
           33  end face 
           34  spindle 
           35  carriage 
           36  threaded element 
           37  vertical movement 
           38  drive 
           39  milling cutter 
           40  axis of rotation 
           41  clearance 
           42  arrow 
           43  arrow 
           44  terminating ring 
           45  inner ring 
           46  projection 
           47  rolling body 
           48  rolling body 
           49  rolling body 
           50  outer ring 
           51  upper ring 
           52  lower ring 
           53  radially widened region 
           54  drive 
           55  electric motor 
           56  plate-shaped continuation 
           57  vertical plate 
           58  side 
           59  driven shaft 
           60  gear wheel 
           61  adaption ring 
           62  disk-shaped extension 
           63  machining ring 
           64  inner cone 
           65  outer cone 
           66  receptacle