Abstract:
A drill having a replaceable cutting head, modified to eliminate forces which would distort the pocket of the drill shank and otherwise concentrate stresses which would cause failure of the drill. The cutting head has a frustoconical depending connecting member received in a receptacle formed in the shank. In different embodiments, contact between the pocket formed in the shank and the cutting head connecting member is limited. In one embodiment, angle of drive surfaces is modified from prior art practice. In another embodiment, transition of at curved joints between vertical and horizontal surfaces is made more gradual. The drill preferably has flutes formed collectively by the shank and cutting head when assembled.

Description:
FIELD OF THE INVENTION 
   The present invention relates to cutting tools, and more particularly to modular drills having replaceable cutting tips. 
   DESCRIPTION OF THE RELATED ART 
   Drills having replaceable cutting tips are known. Illustratively, such tools are shown in U.S. Pat. Nos. 5,957,631 and 6,059,492, both issued to Gil Hecht on Sep. 28, 1999, and May 9, 2000, respectively. The subject drills have replaceable cutting heads which are mounted on shanks. The cutting heads and shanks display continuous and complementing configuration as fluted drills. To this end, each shank has structure for retaining and rotating an associated cutting head. The associated cutting head has complementing structure for being retained and rotated by the shank. While these devices will operate under some circumstances, closer analysis reveals that their useful lives are potentially unduly limited. More specifically, the retaining and drive structure of the shank is subject to deformation and failure during its service life due to concentration of stresses imposed during ordinary service. 
   SUMMARY OF THE INVENTION 
   The present invention provides modifications to drills having replaceable cutting tips, of the type shown in the above referenced patents to Hecht. The modifications of the present invention alter stresses imposed on the shanks such that the shanks either do not undergo deformation and outright failure while in service or alternatively, increase the service life achievable before deformation renders the tool unusable. These modifications generally connote prevention of direct contact of a replaceable cutting head with the shank at certain specified locations. Also, orientations of certain abutting surfaces are modified so that stresses are imposed differently from the original design of Hecht. 
   One specific example of modifications is that of providing a gap between a frustoconical dovetail formed in the cutting head and a cooperating recess formed in the shank, at the forward and rearward areas of mutual contact. The area of contact is limited to that portion between the forward and rearward areas of contact. A second modification is that of altering the angle of drive or torque transmission surfaces from purely radial to inclined relative to a purely radial direction. This has the effect of redistributing forces which would otherwise act on the walls of a pocket formed in the shank. The pocket, which receives the connection structure of the cutting head, then better resists distorting forces. A third modification is that of lengthening at the walls of that portion of the body forming a pocket which receives the cutting head and eliminating sharp corners in this region of the body. In still another modification, the floor of the pocket is modified in the manner of the third modification. 
   These modifications redistribute distorting forces away from portions of the shank which are more susceptible to distortion to portions of the shank better able to withstand these forces. The ultimate effect is to increase the useful service life of the shank due to reduced distortion of the pocket. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the present invention, as well as the advantages derived therefrom, will become clear from the following detailed description made with reference to the drawings in which: 
       FIG. 1  is a partial, exploded perspective view of one embodiment of the modular drill of the present invention. 
       FIG. 2  is an end elevational detail view of the lower end of the upper component of  FIG. 1 , but showing an alternative embodiment thereof. 
       FIG. 3  is a cross sectional view of a further embodiment of the invention. The cross section corresponds to that which could be taken through the components of  FIG. 1  if the components of  FIG. 1  were assembled in axial abutment. 
       FIG. 4A  is a cross sectional view of a still further embodiment of the invention, corresponding to  FIG. 3  but with structure modified therefrom. 
       FIG. 4B  is a cross sectional view of still another embodiment of the invention, corresponding to  FIG. 4A , but with structure modified therefrom. 
       FIG. 5  is a top plan view of an alternative embodiment of the lower component of  FIG. 1 . 
       FIG. 6  is a partial, exploded view of another embodiment of the invention. 
       FIG. 7  is a perspective detail view of a further embodiment of the upper component of  FIG. 1 . 
       FIG. 8  is a partial, side elevational view of a still further embodiment of the invention. 
       FIG. 9  is an enlarged perspective detail view of the embodiment of  FIG. 8 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The documents, patents and patent applications referred to herein, including those pertaining to the prior art, are hereby incorporated by reference in their entirety.  FIG. 1  of the drawings shows a first embodiment of a cutting tool assembly  10  for conducting rotary cutting operations on a work piece (not shown), comprising a tool shank  12  and a replaceable cutting head  14  which is installed on and engages tool shank  12 . Cutting tool assembly  10  is a modular drill which in the preferred embodiments is of the so-called twist drill type, having helical flutes disposed along the sides of the drill. In the embodiment of  FIG. 1 , two flutes are provided in diametric opposition to one another, only one flute being visible. The visible flute has a lateral recess forming part of a flute, or cutting head flute portion  16  formed in cutting head  14 . A corresponding or complementing lateral recess or shank flute portion  18  is formed in shank  12 . The depiction of  FIG. 1  shows cutting head  14  in a position for initially being installed on shank  12 . In this initial position, cutting head  14  is rotated about ninety degrees with respect to rotational axis  20  of cutting tool  10 , which rotational axis  20  is common to both shank  12  and also cutting head  14 . Installation of cutting head  14  requires that cutting head  14  be lowered into abutment or near abutment with shank  12  and rotated in a direction opposite that of rotation during cutting operations. This installation procedure will both interlock cutting head  14  with shank  12  at certain respective mating peripheral surfaces in a manner precluding disengagement in the axial direction, taken with respect to axis  20 , and will also assure abutment of driving surfaces  22 ,  24  of shank  12  with corresponding driven surfaces  26 ,  28  of cutting head  14 . Driving surfaces  22 ,  24  of shank  12  are oriented to abut and bear against driven surfaces  26 ,  28  of cutting head  14  and thereby rotate cutting head  14  in tandem with shank  12  when shank  12  is rotated by its associated cutting tool such as a hand drill, drill press, machine tool, or the like (none shown). 
   Once cutting head  14  is installed on shank  12 , the flute collectively formed by cutting head flute portion  16  and shank flute portion  18  will align to form a flute in generally continuous and undistorted fashion. A similar flute is of course formed on the other side of cutting tool  10 . Although two flutes are preferred, any number of flutes including only one is possible. 
   In the depiction of  FIG. 1 , cutting head flute portion  16  emerges at a leading end  30  of cutting tool  10 . Leading end  30  is defined for semantic purposes, and is that end which engages a work piece (not shown) when cutting. During cutting operations, cutting tool  10  is mounted in the rotary cutting tool, rotated, and advanced progressively into the work piece as cutting progresses. That end of cutting tool located oppositely leading end  30  is termed the trailing end  32 . The terms “leading end  30 ” and “trailing end  32 ” are semantic devices which apply equally to shank  12  and cutting head  14  as they connote directional orientation with respect to longitudinal and rotational axis  20  rather than specific structure. Leading end  30  is that which penetrates a work piece (not shown), and trailing end  32  is that end opposed to leading end  30 . 
   That portion of shank  12  which couples to and rotates cutting head  14  is referred to as pocket  34 . The principal elements of pocket  34  include two generally symmetrical and similar castellated wall sections  36 ,  38 . Wall section  36  will be described, it being understood that wall  38  is a generally symmetrical counterpart thereof. Wall section  36  is essentially a continuation of the body of shank  12  which projects upwardly in the depiction of  FIG. 1  past a central floor portion  40  of shank  12 , along the outer periphery of shank  12 . Wall section  36  has a smooth outer surface  42  which conforms to and is generally coextensive with the generally cylindrical outer surface of cutting tool  10 . At the interior of wall section  36 , the term “interior” referring to those surfaces facing axis  20 , wall section  36  has an internally facing, generally cylindrical face  44  and a frustoconical face  46 . Wall section  36  also has an upwardly facing upper face  48 , an upwardly facing lower face  50 , and a lateral face  52 . Lateral face  52  is located on a side opposite that of driving surface  22 . 
   Cutting head  14  has cutting edges (only cutting edge  54  is visible in  FIG. 1 ), a peripheral generally cylindrical outer surface  56 , and a leading conical surface  58  which conical surface  58  is of course interrupted or incomplete due to presence of the flutes. Cutting edge  54  and leading conical surface  58  collectively form a cutting portion which performs cutting operations to the work piece. 
   Any or all of central floor portion  40 , faces  48  and  50 , and faces formed in wall portion  38  corresponding to faces  48  and  50  serve as abutment surfaces which abut cutting head  14  when cutting head  14  is installed on shank  12 . 
   Cutting head  14  has a shank connection portion opposite the cutting portion, or alternatively stated, facing the trailing end of cutting head  14 , in the form of an interlocking member arranged to retain cutting head  14  within pocket  34  of shank  12 . In the embodiment of  FIG. 1 , this interlocking member comprises a dovetail member  60  which is located centrally along rotational axis  20 . Dovetail member  60  is so-called due to its characteristic frustoconical lateral surface  62  which surface  62  is arranged at an obtuse angle to rotational axis  20 . Dovetail member  60  provides an interlocking member corresponding to and engaging pocket  34 , which pocket  34  serves as an interlocking member of shank  12 . Surrounding dovetail member  60  is a peripheral base surface facing pocket  34 , comprising cutting head faces  64 ,  66 ,  68 , which face downwardly in the depiction of  FIG. 1 . It should be understood at this point that cutting head  14  is generally bilaterally symmetrical, so that cutting head face  64  is generally a mirror image of cutting head face  68 . Similarly, there exists a cutting head face not visible in  FIG. 1  and not identified by reference numeral, which is diametrically opposed to and generally rotationally symmetrical about the central axis. In those embodiments wherein there may be three flutes, for example, there will accordingly be three rather than two similar cutting head faces corresponding to cutting heads  64 ,  66  disposed about the periphery of the cutting head. 
   Faces  64 ,  66  may be stepped, or located at different levels or points along axis  20 , in the same manner as and to correspond to the axial spacing apart of faces  48  and  50  of shank  12 . Any or all of faces  64 ,  66  serve as abutment surfaces for abutting shank  12 . Abutment of faces  64 ,  66  with their corresponding surfaces  48 ,  50  of shank  12  seats cutting head  14  on shank  12  responsive to compressive axial loading. When rotated into the interlocked position with respect to pocket  34 , dovetail member  60  will engage interior frustoconical face  46  of pocket  34 , thereby preventing disengagement in the axial direction away from shank  12 . 
   It is an important feature of the invention that contact between frustoconical face  46  and frustoconical lateral surface  62  be limited such that contact not occur over the entire extent of face  46  or lateral surface  62 . Rather, frustoconical face  46  and frustoconical lateral surface  62  are dimensioned and configured to abut mutually along part of the extent of surface  62  and to avoid making contact along the balance of lateral surface  62 . This characteristic enables pocket  34  to experience minimized forces imposed thereon during cutting operations by cutting head  14 , which forces would otherwise tend to spread or distort pocket  34 . Alternatively stated, although tangential forces remain unchanged, forces imposing a radially outward component are minimized at critical areas. Pocket  34  is thus less subject to distorting forces which would otherwise cause pocket  34  to spread over time of use, thereby shortening the useful life of shank  12 . Representative areas  70 ,  72  of non-contact between face  46  and surface  62  are shown stippled in  FIG. 1 . 
   Non-contact of face  46  and surface  62  may be accomplished in several ways. Turning now to  FIG. 2 , dovetail member  60  is seen in bottom plan. The periphery of dovetail member  60  includes reliefs  74 ,  76  to allow for chip flow after installation, arcuate sections  78 ,  80 , and chamfers  82 ,  84 ,  86 ,  88 . Chamfers  82 ,  84 ,  86 ,  88  reduce the overall diameter of trailing surface  90  of dovetail member  60 . The resulting discrepancy between the full diameter and that at any of chamfer  82 ,  84 ,  86 , or  88  is indicated by arrowheads as gaps  92 ,  94 ,  96 ,  98  which exist between respective chamfers  82 ,  84 ,  86 ,  88  and extensions (shown in broken lines) of the arcuate configuration of the periphery of surface  90 . In the embodiment of  FIG. 2 , then, contact between dovetail member  60  and face  46  of pocket  34  is made along arcuate sections  78  and  80 , but is avoided at chamfers  82 ,  84 ,  86 ,  88 , where the diameter of dovetail member  60  is reduced. The pocket of the shank (neither shown) which corresponds to dovetail member  60  thus contacts only first and second arcuate portions  78 ,  80  of dovetail member  60 , and avoids contacting chamfered portions  82 ,  84 ,  86 ,  88 . 
   Referring now to  FIG. 3 , which is an end view of a dovetail member  100  of a cutting head (not shown in its entirety) installed in a pocket (not shown in its entirety) of a shank, a similar effect is obtained by chamfering walls  102 ,  104  of the pocket. The cutting head associated with dovetail member  100  may be essentially similar to cutting head  14  of  FIG. 1 . The shank of  FIG. 3 , apart from chamfering discussed herein, is essentially similar to shank  12  of  FIG. 1 , similarity extending to the pocket. In the embodiment of  FIG. 3 , chamfered portions  106 ,  108 ,  110 ,  112  formed in internally facing surfaces of pocket walls  102 ,  104  create gaps  114 ,  116 ,  118 ,  120  which provide functions similar to those of gaps  92 ,  94 ,  96 ,  98  of the embodiment of  FIG. 2 . Gaps  114 ,  116 ,  118 ,  120  separate the arcuate sections (not specifically called out by reference numeral) of pocket walls  102 ,  104  from dovetail member  100  at the ends of pocket walls  102 ,  104 . Thus the internally facing surfaces of pocket walls  102 ,  104  contact dovetail member  100  only at their respective arcuate sections and avoid making contact at chamfered portions  106 ,  108 ,  110 ,  112 . The difference between the embodiments of  FIGS. 2 and 3  is that in the embodiment of  FIG. 2 , dovetail member  90  receives chamfering, whereas in the embodiment of  FIG. 3 , walls  102 ,  104  of the pocket of the shank receive chamfering. 
   The dovetail member is limited to an extent less than the full extent of the internally facing surfaces of the pocket when the cutting head is installed in the pocket. More particularly, it is presently preferred that the zone of contact extend along the interior of each of walls  124 A and  126 A within a range of about fifteen to about seventy-five degrees. 
     FIG. 4A  shows an embodiment of the invention utilizing a third way of limiting contact between a dovetail member  122 A of a cutting head (not shown in its entirety) and the pocket of a shank (not shown in its entirety). In  FIG. 4A , walls  124 A,  126 A of the pocket may be identical to their counterparts in  FIG. 1 . In the embodiment of  FIG. 4A , dovetail member  122 A is non-circular in cross section, such as oblong. Radius R 1  defines that part of the outer contour of dovetail member  122 A which contacts wall  124 A, it being understood that a similar radius defines the opposing end of dovetail member  122 A. Radius R 2  defines the inner contours of wall  126 A (a similar radius defines the inner contour of wall  124 A). In the embodiment of  FIG. 4A , the radius of curvature of the interior wall of the pocket is greater than the radius of curvature of the exterior surface of dovetail member  122 A. These radii and related dimensions and configuration are selected and arranged such that contact of dovetail member  122 A with the inside surfaces of walls  124 A,  126 A occurs along only a portion of the inside surfaces of walls  124 A,  126 A. End zones  128 A,  130 A,  132 A,  134 A of walls  124 A,  126 A are not contacted by dovetail member  122 A. This leaves gaps such as gap  136 A at zone  130 A, corresponding gaps (not identified by reference numerals) existing at the other end zones  128 A,  132 A,  134 A. 
     FIG. 4B  shows an alternative to the embodiment of  FIG. 4A . In the embodiment of  FIG. 4B , the radius of curvature of the interior walls of the pocket exceeds the radius of curvature of the exterior surface of the contacting portion of the dovetail member, although this is achieved in a manner different from that of the embodiment of  FIG. 4A . In  FIG. 4B , radius R 1  of dovetail member  122 B originates at the rotational axis of the tool holder. As employed here, the interior surface is that surface of pocket wall  124 B or  126 B which contacts the dovetail member  122 B. 
   The aforementioned embodiments all relate to ways of limiting contact of a dovetail member with pocket walls. The effect of limiting contact in this manner is that the uncontacted portion of the walls of the pockets of the embodiments of  FIGS. 1 ,  2 ,  3 ,  4 A, and  4 B serve to allow tangential deflection of the pocket walls mitigating radial deflection which would create additional stress on the pocket walls. In another type of modification, and referring now to  FIG. 5 , structure is introduced to accommodate forces acting on a pocket of a shank  138 . The pocket of shank  138  includes two walls  140 ,  142  bearing respective driving surfaces  144 ,  146 . In the view of  FIG. 5 , driving surfaces  144 ,  146  are inclined relative to axis of rotation  148 , and thus are visible in this end view. Orientation of surfaces  144 ,  146  is such that if hypothetically extended, as shown by straight projection lines  150 ,  152 , these projection lines  150 ,  152  avoid overlying axis of rotation  148 . Surfaces  144 ,  146  are oriented with respect to the direction of rotation of shank  138 , which as indicated by arrows in  FIG. 5  is counterclockwise. It will be seen that the innermost portion of surface  144 , that being the closer to axis of rotation  148 , is the leading side, whereas the outermost portion of surface  144  is the trailing side. If the direction of rotation were reversed (although this embodiment is not shown), then projection line  150  associated with surface  144  would extend not from the upper left to the lower right, but rather from the lower left to the upper right. The same relationships hold true but in mirror image for surface  146 . By contrast, in the prior art devices, driving surfaces corresponding to surfaces  144  and  146  are generally arranged radially from the axis of rotation. The modification of the present invention redistributes forces which would promote greater or more quickly occurring opening or spreading of the pocket in the prior art designs. 
     FIG. 6  shows a modification to the embodiment of  FIG. 1 . In  FIG. 1 , dovetail member  60  has a relief  154  which modifies the otherwise frustoconical configuration, and an extension  156 . This configuration is modified in the embodiment of  FIG. 6  such that an extension  158  is formed in dovetail member  160  below frustoconical lateral surface  162  of a cutting head  164 . As in the embodiment of  FIG. 1 , lateral surface  162  is oriented at an obtuse angle to axis of rotation  168 . Extension  158  has an outer partially cylindrical surface  166  which is in addition to surface  162 , and a recessed incuse partial surface  170 . To accommodate this additional structure, pocket  172  of shank  174  has surfaces (only surface  176  is visible in  FIG. 6 ) corresponding to surface  166  of extension  158  that do not make contact. Extension  158  also has a beveled or a radiused surface including partial beveled surface  178  and incuse partial beveled or radiused surface  180 . Pocket  172  has corresponding surfaces (only radiused surface  182  is visible) to enable cutting head  164  to be received in pocket  172 . In other respects, both cutting head  164  and shank  174  are similar to their counterparts in other embodiments. 
   It would be possible to eliminate cylindrical surfaces  166 ,  170  from extension  158 . As seen in  FIG. 7 , this is the case in cutting head  184 , which has a dovetail member  186  bearing an upwardly facing frustoconical surface  188  for interlocking to a pocket of a shank (not shown), and a downwardly facing frustoconical surface  190 . An incuse recess  192  is formed in dovetail member  186 . The shank which is to be used with cutting head  184  would of course have configured therein surfaces to accommodate surfaces  188 ,  190 ,  192  of cutting head  184  to assure secure retention of cutting head  184  by surface  188  and the corresponding surface in the pocket. In other respects, both cutting head  184  and its associated shank are functionally and structurally similar to their counterparts in other embodiments of the invention. It will be appreciated that surface  190  does not contact the pocket walls. 
   The effect of the modifications of the embodiments of  FIGS. 6 and 7  is to increase the overall length of frustoconical lateral surface  62 , which in the embodiment of  FIG. 1  is not extended. This increased length, regardless of whether the added length extends straight down (surface  166  of  FIG. 6 ) or is tapered (surface  190  of  FIG. 7 ) allows for a smooth transition between either of the surfaces corresponding to frustoconical surfaces  162  and  188  ( FIGS. 6 and 7 ) of the pocket in relation to the pocket floor thereby minimizing stress concentration. 
   Turning now to  FIG. 8 , a further embodiment is shown wherein a cutting head  194  is installed to a shank  196 . Cutting head  194  has a dovetail member  198  bearing an end surface  200 . Pocket  202  of shank  196  is dimensioned and configured to contact base surface  204  of cutting head  194  for resisting compressive axial forces. Contact with end surface  200  of cutting head  194  is avoided. A shelf  208  and a relief trough  206  are formed in the floor or upwardly facing central surface of pocket  202 . Trough  206  projects into shank  196 , extending towards the trailing end of the tool assembly comprising cutting head  194  and shank  196 . Trough  206  extends across and fully spans the floor from one flute  222  to opposed flute  224 . A better understanding of the geometry of shank  196  will be obtained by also referring to  FIG. 9 . The floor of pocket  202 , which floor collectively encompasses trough  206 , shelf  208 , and shelf  216 , separates and spaces apart one pocket wall  218  from opposed second pocket wall  220 . Referring especially to  FIG. 9 , shelves  208 ,  216  each extend laterally across the floor at respective upper edges  226 ,  228  of relief trough  206 . Each shelf  208  or  216  is associated with one pocket wall  218  or  220 . Relief trough  206  is angularly oriented relative to rotational axis  230  such that each shelf  208  or  216  intersects only flute  222  or  224 , being separated from the other flute  224  or  222  by trough  206 . By way of further explanation, it will be seen that shelf  216  terminates at the right side, as depicted in  FIG. 9 , at flute  224 , whereas at the left side in  FIG. 9 , shelf  216  is spaced apart from flute  222  by a surface  221  which appears as an upward extension of trough  206 . 
   A consequence of this geometry is that trough  206  has at one end a curved end edge  210  which meets the side profile  214  of dovetail member  198  (see  FIG. 8 ) at a tangent at a portion of dovetail member  198 . Curved edge  210  has a significantly greater radius of curvature than does end edge  212  (see  FIG. 8 ) located oppositely from end surface  210 . The greater radius of curvature provides a transition in wall thickness which is gentler than the relatively small curvature seen at edge  212 . Stress concentrations are thereby minimized at the corners of the walls of pocket  202  where dovetail member  198  terminates near the floor of the pocket at relief trough  206 . 
   It will be appreciated that while the dovetail portion of the connector of the cutting head is described in terms of being frustoconical, it would be possible to utilize any configuration wherein there is an upwardly facing surface which can engage one or more corresponding surfaces formed in the retaining structure of the shank. It is preferred to form the dovetail of the connector as frustoconical merely because rotary machining and other inexpensive methods may be employed to form the dovetail. 
   The novel features presented herein may be present in combinations within a single tool made according to the present invention, where such embodiments are geometrically compatible, for example surface  221  also reduces the contact area between the dovetail and the pocket. 
   It will further be appreciated that relative locations of connecting and drive structure of the cutting head and of the shank may be reversed if desired, with appropriate accommodation being made to account for differences in the directions in which forces are imposed. 
   While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.