Abstract:
A tool assembly in which a tool is removably secured to a tool holder. A sleeve of the tool is first fitted onto a shaft of the tool holder and then, by symmetrically radially expanding the shaft, the tool is secured to the tool holder.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a tool assembly comprising a tool holder and a cutting tool for metal cutting operations, the tool assembly being of the type wherein a sleeve of the tool fits on a shaft of the tool holder and is mechanically affixed thereto. 
   BACKGROUND OF THE INVENTION 
   In such tool assemblies a clearance is provided between the sleeve of the tool and the shaft of the tool holder so that the tool can slide onto the shaft before being finally secured to it. Many methods of mechanically securing the tool to the tool holder result in non-symmetrical securing, thereby giving rise to mis-alignment of the cutting tool relative to the tool holder causing radial runout. As is well known, runout decreases the precision and increases the wear of the cutting tool, and reduces the surface quality of the workpiece. 
   It is an object of the present invention to provide a tool assembly that significantly reduces or overcomes the aforementioned disadvantages. 
   The objects of the invention are attained with the subject matter in accordance with the respective claims. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention is directed to a tool assembly comprising a tool holder having a holder axis, and a cutting tool. 
   The tool holder comprises a holder body and a sliding device. The holder body comprising a shaft at a forward end thereof and a holder cavity, the shaft having a peripheral shaft face coaxial with the holder axis, the holder cavity having a holder wall coaxial with the holder axis, at least one section of the holder wall comprising a first forwardly tapering surface. The sliding device has a forward end and a rear end, and at least one peripheral section of the sliding device comprises a second forwardly tapering surface. The cutting tool has a tool axis defining a front to back direction and comprises a tool cavity having a tool wall coaxial with the tool axis. The tool assembly is adjustable between an unassembled position in which the tool holder and cutting tool are separated from one another; and a locked position. In the locked position, the cutting tool is removably secured to a forward end of the tool holder; the sliding device is releasably retained in the holder body with the first forwardly tapering surface abutting the second forwardly facing surface; and at least a portion of the shaft face abuts at least a portion of the tool wall. 
   The sliding device may comprise a flange and a bushing; the second forwardly tapering surface is associated with the flange; and the bushing is provided with an internal thread. 
   The holder cavity may open out to a forward end of the shaft via an aperture having an aperture diameter Da; the flange may has a maximum diameter dL, with dL&gt;Da. In the locked position, the flange is retained in the holder cavity with the first forwardly tapering surface of the holder wall being in abutment with the second forwardly tapering surface of the flange. 
   The flange and the bushing may be separate members. Alternatively the flange and bushing may form an integral one-piece member. 
   The tool assembly, may further comprise a clamping bolt having a clamping face and a threaded portion extending away from the clamping face. The sliding device may comprise a device cavity having a device wall, at least a portion of the device wall forming an internal thread, while the cutting tool comprises an axially oriented sleeve extending to a frontally facing sleeve face. In the locked position, the device wall is coaxial with the holder axis; the threaded portion of the clamping bolt is threadingly engaged in the internal thread; and the clamping face of the clamping bolt abuts the sleeve face of the cutting tool. 
   The tool holder may comprise a fastening screw threadingly engaged in the internal thread and the holder cavity may have a rear surface at a rear end thereof. In the locked position, a rear end of the fastening screw abuts the rear surface of the holder cavity. 
   The device cavity may open out to the forward and rear ends of the sliding device. 
   The cutting tool may have a backwardly facing tool face and an axially oriented sleeve extending to a frontally facing sleeve face, the sleeve extending in a direction away from the backwardly facing tool face. The tool may have a forwardly facing holder face and the tool holder&#39;s shaft extends forwardly and away from the holder face. In the locked position, the backwardly facing tool face at least partially abuts the forwardly facing holder face. 
   The shaft face and tool wall may each lie on a peripheral surface of a cylinder, while the first and second tapering surfaces may each lie on a peripheral surface of a truncated cone. 
   The cutting tool may have an axially oriented sleeve extending to a frontally facing sleeve face; the holder cavity may open out to the forward end of the holder body; and the tool cavity may out to the frontally facing sleeve face and a backwardly facing tool face. 
   The at least a portion of the shaft face may symmetrically abut the at least a portion of the tool wall. 
   In another aspect, the present invention is directed to a method of assembling a tool assembly of the sort discussed above. Such a method comprises: providing such a tool holder with its holder body and sliding device; providing such a cutting tool having a tool axis defining a front to back direction and comprising a tool cavity having a tool wall coaxial with the tool axis; inserting the shaft of the tool holder into the tool cavity of the tool; and urging the sliding device forwardly so that the first tapering surface bears against the second tapering surface and deforms the shaft face outwardly until at least a portion of the shaft face abuts the tool wall. 
   The method may also entail turning a clamping bolt having a threaded portion engaged to an internal thread formed in a device wall of the sliding device, to thereby urge the sliding device forwardly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a tool assembly showing a tool and a clamping bolt removed from a tool holder. 
       FIG. 2  is an exploded perspective view of the tool assembly shown in  FIG. 1 , seen with a two-piece embodiment of a sliding device; 
       FIG. 3  is a partial cross sectional view of the tool holder taken in the plane III-III shown in  FIG. 1 ; 
       FIG. 4  is a perspective view of a one piece embodiment of a sliding device; 
       FIG. 5  is the partial cross sectional view shown in  FIG. 3  with the tool placed on the tool holder and the clamping bolt removed; 
       FIG. 6  is similar to  FIG. 5  but with the sliding device in a forward position; and 
       FIG. 7  is similar to  FIG. 6  but with the clamping bolt threadingly engaged in an internal thread of the two piece sliding device. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Attention is first drawn to  FIGS. 1 and 2  showing a tool assembly  10  having a tool  12  and a clamping bolt  14  in a detached position from a tool holder  16 . The tool holder  16  has a holder body  18 , an anti-rotation screw  20 , a fastening screw  22  and a sliding device  24  which consists of a bushing  26  and a flange  28 . The holder body  18  receives the anti-rotation screw  20 , the fastening screw  22  and the sliding device  24  to form the tool holder  16  for detachably mounting the tool  12 . 
   It should be noted that directional terms appearing throughout the specification and claims, e.g. “forward”, “rear”, “front”, “back” etc., (and derivatives thereof) are used as terms of convenience to distinguish the location of various components of the parts as they appear in the tool assembly  10 . The directional terms are for illustrative purposes only, and are not intended to limit the scope of the appended claims. 
   The tool  12 , which can be used for rotary face or end milling operations, has a tool axis A defining a front to back direction. The tool  12  has a tool body  29  provided with cutting inserts  30  on its periphery, a substantially cylindrical base  31  connected to the body  29 , a hollow sleeve  32  formed proximate a front end of the tool and a tool cavity  34  formed proximate a rear end of the tool. The tool body  29  has a backwardly facing tool face  36  located at a back end of the tool  12  and a frontally facing body face  38 . The sleeve  32 , which has a substantially cylindrical internal surface, extends axially away from the body face  38  at a front end of the tool  12  to a frontally facing sleeve face  40  formed intermediate the body face  38  and the tool face  36 . The tool cavity  34  opens out to the sleeve face  40  and tool face  36  and has a cylindrical shaped tool wall  42  coaxial with the tool axis A and having a tool diameter Dt. Thus, the tool cavity  34  communicates with the sleeve  32 . The base  31  of the tool  12  has two identical key ways  44  which are distributed with 180° symmetry about the tool axis A. 
   Attention is now additionally drawn to  FIG. 3 . The holder body  18 , anti-rotation screw  20 , fastening screw  22  and sliding device  24  will each be described from hereon in its respective position in the tool holder  16  and in relation to a holder axis B of the tool holder  16 . The holder axis B defines a forward to rear direction. The holder body  18  has a forwardly facing holder face  46 , two identical drive keys  48 , a shaft  50 , a holder cavity  52  and a transversely directed threaded bore  64 . The drive keys  48  are distributed with 180° symmetry about the holder axis B and in the tool assembly  10  are located within the key ways  44  of the tool  12  for transferring torque thereto. 
   The shaft  50  has a cylindrical peripheral shaft face  54  coaxial with the holder axis B and extending away from the holder face  46 . The shaft face  54  has a shaft diameter Dc. The holder cavity  52  opens out to a forward end of the shaft  50  via an aperture  56  having an aperture diameter Da. The holder cavity  52  has an axially extending holder wall  58  and a forwardly facing rear surface  60  at a rear end thereof. A forward section of the holder wall  58  lies on a first tapering surface  62  which tapers forwardly to the aperture  56 . The first tapering surface  62  forms a peripheral surface of an imaginary truncated cone. The threaded bore  64  has a longitudinal bore axis C which is perpendicular to the holder axis B, opens out to a peripheral surface of the holder body  18  adjacent the shaft  50  and communicates with the holder cavity  52 . 
   The sliding device  24  extends along the holder axis B from a rear end thereof to a forward end thereof. The sliding device  24  has a device cavity  66 . The device cavity  66  (See  FIG. 3 ) has a device wall  68  which is coaxial with the holder axis B, extends through the flange  28  and bushing  26  and opens out to the forward and rear ends of the sliding device  24 . The flange  28  has a peripheral surface which comprises two tapering sections  70  and two flat sections  72  (only one flat section  72  can be seen in  FIG. 2 ). The tapering sections  70  are identical and are distributed with 180° symmetry about the holder axis B. Each flat section  72  is located circumferentially between the tapering sections  70  on opposing sides of the peripheral surface of the flange  28 . The flat sections  72  are parallel to each other and are spaced apart by a first distance d 1 . The tapering sections  70  taper forwardly from a maximum diameter dL to the forward end of the sliding device  24  and lie on a second tapering surface  74  which forms a peripheral surface of an imaginary truncated cone. 
   The bushing  26  has a cylindrical peripheral surface having a bushing diameter Db and an internal thread  76  formed on a portion of the device wall  68  passing therethrough. A holding recess  78  formed on the peripheral surface of the bushing  26  opens out to the rear end of the sliding device  24 . The bushing diameter Db is smaller than the aperture diameter Da so that the bushing  26  may be received in the holder cavity  52  via the aperture  56 . However, the maximum diameter dL of the tapering sections  70  is larger than the aperture diameter Da. To accommodate the flange  28  in the holder cavity  52 , the first distance d 1  of the flange  28  is smaller than the aperture diameter Da so that the flange  28  may be received in the holder cavity  52  via the aperture  56  when the flange is oriented on its side in such a manner that its tapering sections  70  generally intersect the holder axis B and its flat sections  72  are generally parallel to the holder axis B. 
   The sliding device  24 , comprising the flange  28  and the bushing  26 , may be formed as a single one-piece integral member, and therefore the tapering section  70  of the flange  28  may extend along its full peripheral circumference ( FIG. 4 ). In such a case, the shaft  50  would have to be made of two separable portions separably joined at a join, so that the forward portion of the shaft can be separated from the rear portion of the shaft to enable the sliding device  24  to be positioned in the holder cavity  52 . 
   The sliding device  24  is slidably retained in the holder cavity  52 . Rotation of the bushing  26  in a given direction around the holder axis B is prevented in the tool holder  16  by the anti-rotation screw  20  which is threadingly engaged in the threaded bore  64  of the holder body  18  and protrudes into the holding recess  78  of the bushing  26 . The fastening screw  22  has a cylindrical shape and is threadingly engaged in the internal thread  76  of the bushing  26 . 
   Attention is now drawn to  FIGS. 5 to 7  to show how the tool  12  is mounted on the tool holder  16 . The tool  12  is first placed on the tool holder  16  in such a manner that the shaft  50  of the holder body  18  is located in the tool cavity  34 , each drive key  48  is located in a respective key way  44  (not shown) and the tool face  36  faces the holder face  46  ( FIG. 5 ). The tool diameter Dt is slightly larger than the shaft diameter Dc to form a clearance which enables the shaft  50  to easily slide into the tool cavity  34 . This clearance may increase non-alignment in the tool assembly  10  between the tool axis A and the holder axis B and thereby increase the wear of the cutting means of the tool  12  and reduce surface quality of a workpiece being machined. The fastening screw  22 , which is then screwed further into the internal thread  76  of the bushing  26 , abuts the rear surface  60  of the holder cavity  52  with a rear end  23  thereof and then urges the sliding device  24  forwardly towards a forward position which brings the tool assembly  10  towards a locked position ( FIG. 6 ). As a result, the tapering sections  70  of the flange  28  which lie on the second tapering surface  74  abut and bear against the forward portion of the holder cavity  52  which lies on the first tapering surface  62  and thereby cause the shaft  50  to elastically deform and symmetrically expand radially outwardly. 
   This symmetrical radial expansion will continue until, at least adjacent the tapering surfaces  62 ,  74 , the clearance between the shaft face  54  and the tool wall  42  is eliminated and at least a portion of the shaft face  54  symmetrically abuts at least a portion of the tool wall  42 . It should be noted that the symmetrical radial expansion of the shaft  50  helps center the tool  12  on the tool holder  16  and thereby increases alignment between the tool axis A and the holder axis B. The clamping bolt  14  has a cross shaped bolt head  45  (best seen in  FIGS. 1 and 2 ) having a rearwardly facing clamping face  82  and a cylindrical threaded portion  84  extending away from the clamping face  82 . The threaded portion  84  is finally screwed into the internal thread  76  of the bushing  26  until the clamping face  82  and the sleeve face  40  abut. By screwing the threaded portion  84  further into the internal thread  76 , the tool  12  is urged rearwardly until the backwardly facing tool face  36  and the forwardly facing holder face  46  abut and then the sliding device  24  is urged further forwardly to the forward position thereby causing the shaft  50  to elastically deform and radially expand further more until the locked position of the tool assembly  10  is achieved ( FIG. 7 ). 
   It will be appreciated that if the flange  28  shown in  FIG. 2  is used (with the two flat section  72 ), then in the locked position the shaft  50  will be elliptical in shape, so that it will have 180° symmetry about the tool axis A, whereas if the flange  28  shown in  FIG. 4  is used, then in the locked position the shaft  50  will be circular in shape, so that it will be completely symmetrical about the tool axis A. 
   There are situations in which it is not required to use the fastening screw  22  in addition to the clamping bolt  14 . In these situations, the clamping bolt  14  will both urge the sliding device  24  forwardly to radially expand the shaft  50  until its shaft face  54  symmetrically abuts the tool wall  42 , and urge the tool  12  rearwardly until the tool face  36  and holder face  46  abut. 
   Although the present invention has been described to a certain degree of particularity, it should be understood that various alterations and modifications could be made without departing from the scope of the invention as hereinafter claimed.