Abstract:
A cutting tool for rotary cutting includes a rotatable basic body and a replaceable cutting part or loose top, which is connectable to the basic body via a male/female coupling, which includes a groove and a male part. The groove is formed in a front end of the basic body and is delimited by a bottom surface and two side surfaces. The male part is insertable into the groove along the axis of rotation and protrudes rearwardly from the loose top. The male part has an end surface and two flank surfaces. In the front part of the basic body a forwardly open slot is formed, which separates two elastically deflectable legs wich clamp the male part in the groove. In either the end surface or the bottom surface a recess is formed for receiving a projection on the other surface. The recess is larger than the projection in order to enable the male part to reciprocate a short distance in the groove, whereby the loose top is self-centering with respect to the axis of rotation.

Description:
The present application claims priority under 35 U.S.C. § 119 to Patent Application Serial No. 0401010-4 filed in Sweden on Apr. 20, 2004. 
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a rotatable tool intended for chip removing or chip forming machining and being of the type that comprises a basic body, as well as a replaceable cutting part, which is clamped to the basic body via a male/female coupling. The coupling includes, on one hand, a groove formed in a front end of the basic body, which groove is delimited by a bottom surface and two side surfaces, and on the other hand a male part insertable into the groove and protruding rearward from the cutting part. The male part has an end surface and two flank surfaces. In the front part of the basic body a forwardly open slot is formed, which separates two elastically deflectable legs with the purpose of holding the male part clamped in the groove. In one of the end and bottom surfaces, a seating recess is formed for the receipt of a projection disposed on the other of the end and bottom surfaces. 
     BACKGROUND OF THE INVENTION 
     Cutting tools of the type that makes use of a basic body, as well as a separate, replaceable cutting part, may in practice comprise drilling tools, milling tools, such as end mills or slitting cutters, thread cutters, etc. Usually, the basic body consists of an elongate shaft of a cylindrical basic shape. In modern machine tools, the basic bodies are so sophisticated and expensive that they, for economical reasons, cannot be integrated with the cutting part, which constitutes the wear part of the tool and has a limited service life. In other words, it is profitable to make the actual cutting part in the form of a separate, releasable unit, which by those skilled in the art usually is denominated “loose top”, and which can be exchanged after wear, while the expensive basic body can be used for a longer time (usually 10 to 20 exchanges). In practice, the loose top is manufactured entirely or partly from a hard, wear-resistant material, such as cemented carbide or the like, while the basic body is made from a material having greater elasticity, e.g., steel. It should also be pointed out that tools of the kind in question primarily—though not necessarily—are intended for the machining of workpieces of metal. 
     The development of loose top tools is particularly intense and interesting in the field of drilling. For drilling purposes, either simple drilling machines or multioperation machines are used, which in both cases include a strong and rigidly mounted machine spindle or holder, in which a rear end of the basic body of the cutting tool can be fixed, at the same time as the front end of the basic body is freely available for the mounting and dismounting of the loose tops that should carry out the cutting or chip removing task in the workpieces in question. Under absolutely ideal conditions, not only the geometrical center axis of the basic body, but also the geometrical center axis of the loose top should coincide exactly with the geometrical center axis of the machine spindle, in order to generate a hole having optimum precision in respect of shape as well as position in the workpiece. However, in practice it is difficult to reach an optimum precision, above all because of inevitable tolerances in the interface between the loose top and the basic body, which, as known, are individually manufactured in different operations and from different materials, but also because of various form defects in the basic body as well as the loose top. Therefore, in reality the result will not infrequently be that the drill wobbles when entering a workpiece, i.e., the tip of the loose top is unintentionally located offset from the geometrical center axis of the machine spindle, which determines the geometrical position of the hole to be made. Instead of moving linearly into the workpiece, the tip of the loose top, therefore, initially describes a circling or planetary motion before being stabilized in a linear track of motion that may be located more or less far from the intended track of motion. 
     DESCRIPTION OF THE PRIOR ART 
     A cutting tool of the type initially mentioned is previously known from SE 0103752-2 (corresponding to U.S. Publication No. 2003/103824). However, a disadvantage of this tool is that the male part of the loose top is formed in such a way that it has to be inserted from the side into the receiving groove in the basic body. In order to obviate this disadvantage, a tool has been developed, which is the subject of SE 0400056-8, and which makes it possible to insert the male part of the loose top axially into the groove of the basic body, i.e., perpendiclarly to the axis of rotation. In this case, the male part of the loose top is formed with a rotationally-symmetrically formed centering protrusion (i.e., symmetrical about the axis of rotation), which is arranged to engage a likewise rotationally-symmetrically formed recess in the bottom surface of the groove. The purpose of the centering protrusion is to center the loose top in relation to the basic body, and for this purpose the centering protrusion has a conical envelope surface, the largest and smallest diameters of which are so adjusted, that a linear contact is established between that surface and a substantially circular edge that defines the mouth of the recess. This construction requires extremely good manufacturing precision, not only in connection with the production of the loose top made from cemented carbide, but also in connection with the production of the basic body, which consists of steel. In addition, no guarantee for the machining precision will arise, even if the loose top in fact would come to be centered exactly in relation to the basic body. Thus, even small form defects in the basic body may lead to the loose top&#39;s own axis being non-coincident with the center axis of the machine spindle. 
     OBJECTS AND FEATURES OF THE INVENTION 
     The present invention aims at obviating the above-mentioned drawbacks of previously known cutting tools and at providing an improved cutting tool. Therefore, a primary object of the invention is to provide a cutting tool in particular intended for drilling, the loose top of which can be centered in a very exact way in relation to the axis of the machine spindle. Another object of the invention is to realize an improved machining precision by means of simple and inexpensive means. It is also an object to provide a tool in which the interface between the loose top and the basic body is of such a nature that the user/operator, in connection with the mounting of the loose top, is given a reassured feeling in that the loose top is perceived as being fixed in a distinct and reliable way in the groove of the basic body. 
     According to the invention, at least the primary object is attained by a rotable tool for chip removing machining, comprising a body and a cutting part. The body defines a longitudinal center axis and includes a groove and a forwardly open slot. The groove is formed in an axial front end of the body and includes an axially forwardly facing bottom surface and two side surfaces. The forwardly open slot is formed in the bottom surface, wherein the slot and the groove separate a pair of leg portions of the body that are elastically movable away from and toward each other to respectively expand and contract the groove. The cutting part is replaceably mounted to the body and includes an axially rearwardly projecting male part axially clamped in the groove between the leg portions. The male part includes an end surface, and two flank surfaces. The end surface faces the bottom surface of the groove. The two flank surfaces face and engage respective ones of the side surfaces of the groove in clamping relationship. Either the end surface or the bottom surface has a seating recess formed therein which receives a projection disposed on the other of the end surface and the bottom surface. The seating recess receives the projection with play in a direction parallel to the side surfaces and the flank surfaces, to enable the cutting part to move relative to the body in said direction during a cutting operation, wherein the cutting part is self centering with the axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, preferred embodiments of the invention are depicted, wherein: 
         FIG. 1  is a perspective view of a cutting tool being in the form of a drill according to the invention and mounted in a rotatable machine spindle, the basic body of the tool being illustrated in phantom view. 
         FIG. 2  is an enlarged perspective exploded view showing a part of a basic body as well as a cutting part or loose top separated from the basic body of a first embodiment of the tool according to the invention. 
         FIG. 3  is an end view of the basic body according to  FIG. 2 . 
         FIG. 4  is an end view of the loose top according to  FIG. 2 . 
         FIG. 5  is a longitudinal section A—A through the tool in assembled state. 
         FIG. 6  is an extremely enlarged section through a part of the interface between the loose top and the basic body, more precisely in the area of a projection received in a seating, the projection being shown centered in relation to the seating. 
         FIG. 7  is a section corresponding to  FIG. 6  and showing the projection in a laterally displaced position in the seating. 
         FIG. 8  is an exploded view corresponding to  FIG. 2  and showing a second, alternative embodiment of the tool according to the invention. 
         FIG. 9  is an exploded view showing a third, alternative embodiment of the invention. 
         FIG. 10  is a side view of a basic body. 
         FIG. 11  is an end view of the basic body of  FIG. 10 . 
         FIG. 12  is an end view of a loose top co-operating with the basic body according to  FIGS. 10 and 11 , and 
         FIG. 13  is an end view of another embodiment of a loose top. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In  FIG. 1 , numeral  1  generally designates a cutting tool in the form of a drill, which is shown mounted in a holder  2 , which in turn is mounted in a rotatable machine spindle  3 . The drill is composed of a basic body  4  illustrated in phantom view, as well as a releasable cutting part or loose top  5 . In this case, the basic body  4  comprises a comparatively narrow, cylindrical shaft, which at a rear end has a thickened portion  6 , which can be fixed in the holder  2 . Said holder is, in turn, fixable in a hollow space  7  in the spindle  3 . With the purpose of taking part in the transfer of torque to the drill, two shoulders  9  are arranged on the front surface of the spindle  3 , which shoulders engage in recesses in the holder  2 . In the shaft  4 , helicoidal chip channels  10  are formed. As is clearly seen in  FIG. 1 , the loose top  5  is mounted on the free, front end of the shaft  4 . 
     In  FIG. 1 , C designates an imaginary geometrical center line, which is shown in the form of a single dash-dotted line, which extends from the rear end of the spindle  3  to the front end of the loose top  5 . However, in practice, each of the components  2 ,  3 ,  4  and  5  has its own geometrical center axis. Thus, the spindle  3  has a center axis, which is designated C 3 , while the individual center axes of the holder  2 , the basic body  4  and the loose top  5  are designated C 2 , C 4  and C 5 , respectively. Essential for the machining precision of the tool is that the center axis C 5  of the loose top  5  is coincident with the center axis C 3  of the spindle  3  during a drilling operation. Thus, the object of the invention is to guarantee that the center axis C 5  of the loose top  5  coincides with the center axis C 3  of the spindle  3 , while it is incidental whether the center axes C 2  and C 4  are absolutely concentric with the axes C 3  and C 5 . It shold be noted that an “axis” is considered herein to be endless, i.e., it does not lie only in the boundaries of its respective rotary element. Thus, two axes “coincide” with one another when they are exactly aligned with one another. 
     Reference is now made to  FIG. 2 , which illustrates the design of an interface between the drill or the basic body  4  and the loose top  5  in accordance with a first embodiment of the invention. 
     In the axial front end of the basic body  4 , a groove  11  is formed, in the bottom surfcae  14  of which a slot  12  mouths. The slot, together with the groove  11 , separates two elastically deflectable legs  13  from one another. The groove  11  is delimited by the bottom surface  14  and two side surfaces  15 , the latter defining a jaw, the shape of which tapers (narrows) in a wedge-shaped way in the forward direction (upward in the drawing). In one of the legs  13 , there is a hole  16  for a tightening screw (not shown) that can abut the other leg, by means of which the two legs can be elastically distanced somewhat from each other by deflection in order to widen the groove and enable an axial insertion of the loose top  5  into the groove  16 . 
     The loose top  5  has a rotationally symmetrical basic shape in that it has a circular outer contour shape adjacent to a cylindrical or rearwardly slightly conical envelope surface  17 . The front surface  18  (see also  FIGS. 4 and 5 ) on the loose top is conical and ends in a central tip  19 . Generally, the loose top has an outer diameter, which is somewhat larger than the diameter of the basic body  4 . In the envelope surface  17  on the loose top, two concavely curved limiting surfaces  20  are formed, which connect to the surfaces  10  and define chip channels in the loose top. In the front part of the loose top, cutting edges  21  are formed adjacent to the chip channels  20 , which edges are diametrically opposed each other, i.e., equidistantly spaced-apart by 180°. In other words, the loose top has a symmetrical basic geometry. At the rear or inner end thereof, the loose top has an axially rearwardly extending male part  22  for engagement with the groove  11 . Said male part is delimited by a rearwardly facing end surface  23  and two flank surfaces  24 , which are inclined in order to correspond to the wedge-shape of the groove defined by the inclined side surfaces  15 . On both sides of the male part  22 , there are planar, axial facing force-transmitting surfaces  25  for co-operation with uniform surfaces  26  located on both sides of the groove  11 . 
     On the rear end surface  23  of the male part  22 , a projection  27  is formed intended to engage a seating, or recess,  28  in the bottom surface  14  of the groove  11 . 
     The loose top  5  is made entirely or partly from cemented carbide or other wear-resistant material, while the basic body  4  is made from a material having considerably greater elasticity, e.g., steel. Steel is preferred by virtue of the inherent elasticity or flexibility thereof, which makes it possible to resiliently deflect the legs  13  that are spaced-apart by the slot  12 . 
     As far as the shown tool has been described hitherto, the same is in all essentials previously known. Characteristic of previously known tools is that the projection  27  has had the purpose of centring the loose top in an immovable state in relation to the basic body, more precisely by having such a shape, that the projection, upon insertion in the seating  28 , gets in close (snug) contact with the seating. 
     Characteristic of the tool according to the present invention is that a dimension of the seating  28  in a direction parallel to the surfaces  15 ,  24  is larger than a corresonding dimension of the projection  27 , in order to enable the male part  22  of the loose top  5  to move reciprocatingly (with “play”) in the groove  11  during a cutting operation and thereby allow self-centring of the loose top with reference to the axis C. More precisely, due to such “play” the loose top  5 , despite being frictionally clamped by the legs  13 , is allowed to slide and assume a centered position, in which the center axis C 5  thereof coincides with the center axis C of the spindle  3 , without the center axis C 4  of the basic body  4  necessarily coinciding with the axis C 3 . 
     In the embodiment example according to  FIGS. 2–7 , the projection  27  and the seating  28  have a quadrangular basic shape. Thus, the projection  27  is defined by four planar flank surfaces  29 , as well as a lower end surface  30 , which suitably is planar. As is clearly seen in  FIGS. 6 and 7 , the flank surfaces  29  are inclined in relation to the end surface  23  of the male part, more precisely in the direction inward toward each other so that the projection generally tapers in a direction away from the surface  23 . The seating  28  may advantageously have generally the same shape as the projection, in that the same is delimited by four planar and inclined side surfaces  31  and a planar bottom surface  32 . However, in general the seating is larger than the projection. In this connection, it should be pointed out that surface contact between the loose top  5  and the basic body  4  is established solely between the end surfaces  25 ,  26  and between the side surfaces  15  of the groove and the flank surfaces  24  of the male part, respectively. This means that the end surface  23  of the male part is distanced from the bottom surface of the groove  14 , such as clearly is seen in  FIGS. 6 and 7 . Furthermore, the height of the projection  27  is so adapted in relation to the depth of the seating  28 , that the surfaces  30  and  32  do not contact each other. In other words, the projection does not bottom-out in the seating. 
     In  FIG. 6 , the projection  27  is shown in a neutral intermediate position in the seating  28 , i.e., the two flank surfaces  29  on the projection are distanced from the corresponding side surfaces  31  in the seating. From this neutral position, which is defined by a reference line R, the projection  27  is movable reciprocatingly in the plane that is defined by the groove  11 , i.e., parallel to the side surfaces  15  of the groove. However, the projection cannot move perpendicularly to said plane, because the deflectable legs  13  are kept pressed against the flank surfaces  24  of the male part  22  and guide the male part linearly. In this connection, it should be emphasized that the mobility of the projection  27  in the groove  11  does not mean that the projection is freely movable. On the contrary, the deflectable legs  13  guarantee a prestress of the projection in the arbitrary position that the projection and the loose top assume in connection with the mounting. Therefore, lateral displacement of the loose top takes place first when the loose top has entered a workpiece and is subjected to considerable cutting forces which can overcome the clamping forces. In other words, the legs clamp the projection in any given position as long as the drill rotates without having entered the workpiece. 
     In  FIG. 7 , the projection  27 —after having been subjected to cutting forces—is shown displaced rightwards to an end position, in which the right flank surface  29  abuts against the right side surface  31  of the seating. The distance d, with which the projection is moved from the position according to  FIG. 6  to the position according to  FIG. 7 , constitutes a measure of the size difference between the seating and the projection. In other words, the measure d can be regarded to define the radial mobility of the loose top (the mobility diametrically=2d). 
     The difference between the width of the seating  28  and the width of the projection as seen in the longitudinal extension of the groove varies in practice depending on the diameters of the drills, more precisely in such a way that the difference is small in drills of small diameters and larger in drills of larger diameters. However, in all events, the difference between the width of the seating and the width of the projection (i.e., the “play”) should amount to at least 0.02 mm (d=0.01 mm) and at most 0.20 mm (d=0.10 mm). In practice, the difference between the width of the seating and the width of the projection may advantageously fall within the range of 0.04–0.16 mm, suitably 0.07–0.13 mm. 
     By the fact that the loose top is radially movable within the limits determined by the measure 2d, a self-centring of the same is enabled in connection with the entering of the drill into a workpiece. Thus, if the center axis C 4  of the basic body  4  in the area of the interface against the loose top, for one reason or the other, e.g., tolerances in the interface and/or minor shape defects in the basic body and/or the holder  2 , does not coincide with the center axis C 3  of the spindle  3 , then the loose top will be displaced to the center axis C 3 . This occurs when the loose top has entered the workpiece and is subjected to cutting forces that are considerably greater than the prestressing (clamping) force exerted by the legs  13  against the male part  22  of the loose top. 
     In the tool according to  FIGS. 2–7 , the seating  28  is entirely located to the half of the bottom surface  14  that is situated on one side of the slot  12 , in addition to which the projection  27  is laterally displaced correspondingly. 
     Reference is now made to  FIG. 8 , which illustrates an alternative embodiment of a drill  1 A, in which an elongate seating  28  bridges over the slot  12 . More precisely, in this case the seating is made by two uniform recess portions, which are axially forwardly open and mouth in the slot  12 . The projection  27  of the loose top  5  has the same elongate basic shape as the seating  28 , although the width of the projection measured between the side surfaces  29  is smaller than the width of the seating measured between the side surfaces  31 . By the fact that the elongate projection together with the seating are oriented perpendicularly to the radial direction of motion of the loose top  5 , the contact surfaces  29 ,  31  that form stops in the two outer positions of the loose top are enlarged. 
     Another difference between the previously described embodiment and the embodiment according to  FIG. 8 , is that the latter lacks a tightening screw for the deflection of the legs  13 . Instead, a cross-section-wise oval key recess  33  is formed adjacent to the slot  12  for a likewise cross-section-wise oval key, by means of which the legs can be bent apart. 
     In  FIG. 9 , an additional alternative embodiment of the drill  1 B is shown. In this case, a seating  28  is formed in the male part  22  of the loose top  5 . More precisely, the seating  28  is in the shape of an elongate, cross-section-wise V-shaped groove, which is countersunk in the surface  23  and extends along the entire width of the male part. A projection  27  is in turn formed in the groove of the basic body  4 . More precisely, the projection is of the shape of a cross-section-wise V-shaped bulge or ridge, which projects from the bottom surface of the groove  14 . Advantageously, the ridge extends along the entire width of the groove, although it is bisected by the slot  12 . In the above described way, the width of the groove  28  is larger than the width of the ridge  27 , in order to enable reciprocating displacement of the male part  22  a short distance in the groove. 
     Reference is now made to  FIGS. 10–12 , which illustrate that the groove  11  in the basic body  4  is oriented in a plane P. In  FIG. 12 , a symmetrical loose top is shown, the two equidistantly separated, i.e., diametrically opposed cutting edges  21  of which are intersected by a radial plane designated EP. It would be ideal to orientate the flank surfaces  24  of the male part  22  of the loose top parallel to the plane EP, but for reasons of geometry/construction, this is difficult or impossible (depending on the formation of the chip channels  10 ,  20 ). Therefore, the male part usually has to be sloped such that the flank surfaces  24  thereof are oriented at a certain angle a to the radial plane EP. This angle a, which in the example according to  FIG. 12  amounts to about 15°, should be as small as possible, and in all events not exceed 30°. Suitably, the angle a should be smaller than 20 to 25°. 
       FIG. 13  illustrates another embodiment of a loose top. In this case, the male part  22  is rotated clockwise in relation to the male part according to  FIG. 12 . Also in this case, the angle a should not exceed 30°. 
     FEASIBLE MODIFICATIONS OF THE INVENTION 
     The invention is not solely limited to the embodiments described above and illustrated in the drawings. Thus, the geometrical shape of the projection as well as the appurtenant seating may be varied in miscellaneous ways within the scope of the subsequent claims. For instance, the projection and the seating, respectively, may be of a rotationally symmetrical basic shape, such as cylindrical or slightly conical basic shape.