Patent Publication Number: US-2007116539-A1

Title: Cutting Tool Assembly Having Three-Start Threaded Coupling system

Description:
FIELD OF THE INVENTION  
      The present invention relates to a cutting tool assembly and in particular to a cutting tool assembly employing threaded coupling to releasably secure replaceable cutting-heads to a tool shank.  
     BACKGROUND OF THE INVENTION  
      Such cutting tool assemblies are known in the art. U.S. Pat. No. 6,485,220, for example, discloses a cutting tool assembly having a longitudinal axis A and comprising a male member and a female member. Each of the male and female members is formed with a threaded coupling portion, an annular abutment surface disposed perpendicularly to the longitudinal axis A and a frustoconical centering portion extending between the annular shoulder and the threaded coupling portion. The male member is mounted in the female member and rotated relative thereto, till the frustoconical centering portion and the annular abutment surface of the male member abuts the frustoconical centering portion and the annular abutment surface of the female member. The abutment between the frustoconical surfaces ensures concentricity between the male and the female members.  
      U.S. Pat. No. 5,114,286 discloses an interchangeable cutting tool alignment and positioning system comprising a first tool segment having a male coupler and a second tool segment having a female coupler. The male coupler comprises a pilot, a male thread and a concentric aligner. The female coupler comprises a pilot bore, a female thread and a concentric bore. When the male thread is fully engaged with the female thread, the pilot extends to within the pilot bore, and the concentric aligner extends to within the concentric bore. The diametrical sizing of the concentric aligner and the pilot must match that of the concentric bore and the pilot bore, respectively, to a very close tolerance, in order to provide means by which axial misalignment of the first and second tool segments is prevented. The close tolerance fit of the concentric aligner to the concentric bore and of the pilot to the pilot bore, acting in concert at either ends of the male and female threads, essentially prevents bending moments which may cause misalignment of the assembled tool segments about the tool rotational axis.  
      It is the object of the present invention to provide a cutting tool assembly in which the cutting-head and the shank are axially aligned by the threaded coupling thereof. This object is attained with the subject matter in accordance with the claims.  
     SUMMARY OF THE INVENTION  
      In accordance with the present invention there is preferably provided a cutting tool assembly having a tool longitudinal axis T defining front-to-rear direction and comprising a cutting-head threadingly secured to a tool shank. The cutting-head comprises a three-start, threaded head coupling portion having three head threads. The tool shank has a shank forward portion which comprises a three-start, threaded shank coupling portion having three shank threads.  
      Preferably, the cutting-head comprises a forward cutting portion having a rearwardly facing cutting-head shoulder, and the tool-shank comprises a shank forward portion having a forwardly facing shank coupling shoulder in abutment with the cutting-head shoulder.  
      Further preferably, the cutting-head and tool shank shoulders are perpendicular to the tool longitudinal axis T.  
      Yet further preferably, the cutting-head and tool shank shoulders have an annular shape and are rotationally symmetrical with respect to the tool longitudinal axis T.  
      Typically, the three head threads have each a head thread start. The three head thread starts are circumferentially spaced apart from each other by a head thread start angle σ H . The three shank threads have each a shank thread start. The shank thread starts are circumferentially spaced apart from each other by a shank thread start angle σ S . The head and shank thread start angles σ H , σ S , are of 120°.  
      Preferably, each of the three head threads starts at the respective head thread start adjacent a head coupling rear end and extends forwardly to terminate adjacent the cutting-head shoulder.  
      If desired, the shank forward portion comprises a cylindrical relief bore extending rearwardly from the tool shank shoulder coaxially with the tool longitudinal axis T to merge with the shank coupling portion, so that a forward gap exists between the relief bore and the head coupling portion.  
      If further desired, the shank coupling portion extends rearwardly to a shank coupling rear end, and a rear gap exists between the head and shank coupling rear ends.  
      In another aspect, the present invention is directed to a cutting head having a head longitudinal axis H defining a front to rear direction, the cutting head comprising a three-start, threaded head coupling portion having three head threads. 
    
    
     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 side view and a partial section view of detached cutting-head and tool shank of a cutting tool assembly in accordance with the present invention;  
       FIG. 2  is a rear view of the cutting-head shown in  FIG. 1 ;  
       FIG. 3  is a front view of the shank shown in  FIG. 1 ;  
       FIG. 4  is a side view and a partial section view of attached cutting-head and tool shank of the cutting tool assembly shown in  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Attention is drawn to  FIG. 1 . A cutting tool assembly  20  is formed by detachably securing a cutting-head  22  to a tool shank  24 . The cutting tool assembly  20  has a tool longitudinal axis T defining front-to-rear direction. The cutting-head  22  is preferably made of cemented carbide or other appropriate materials (such as ceramics or cermets).  
      The cutting-head  22  has a cutting portion  26  integrally formed with and extending forwardly from a head coupling portion  28 . The cutting portion  26  and the head coupling portion  28  are coaxial, having a common head longitudinal axis H. The cutting portion  26  has a rearwardly facing, annular cutting-head shoulder  30  which is rotationally symmetric about the head longitudinal axis H and is perpendicular thereto. The head coupling portion  28  extends rearwardly from the cutting-head shoulder  30  coaxially with the head longitudinal axis H to a head coupling rear end  36 .  
      The head coupling portion  28  has the form of a three-start, threaded cylindrical stem, having three independent, substantially identical, parallel head threads  38 ′,  38 ″,  38 ″′ which are external, or “male”, threads. Each of the three head threads  38 ′,  38 ″,  38 ′″ starts at a head thread start  40 ′,  40 ″,  40 ′″ adjacent the head coupling rear end  36  and extends forwardly to terminate in a head thread end (only one head thread end  42 ″ is seen) adjacent the cutting-head shoulder  30 . The head thread starts  40 ′,  40 ″,  40 ′″ are circumferentially spaced apart by a head thread start angle σ H  of 120° ( FIG. 2 ).  
      The tool shank  24  has a shank body portion  50  which extends rearwardly from a shank forward portion  52 . The shank body portion  50  terminates at a shank body rear end (not shown) adapted to be attached to a metal cutting machine (not shown). The tool shank  24 , shank body portion  50  and shank forward portion  52  are coaxial, having a common shank longitudinal axis S. The shank forward portion  52  terminates in an axially forwardly facing tool shank shoulder  54 . A shank coupling portion  56 , in the form of a threaded cylindrical bore, merges with the tool shank shoulder  54  through a cylindrical relief bore  57  and extends rearwardly therefrom , terminating at a shank coupling rear end  60 . The relief bore  57  and the shank coupling portion  56  are coaxial with the shank longitudinal axis S. The tool shank shoulder  54  is annular in shape, and extends radially outwardly from the relief bore  57  to a shank forward peripheral surface  62 , and is rotationally symmetric with respect to the shank longitudinal axis S and perpendicular thereto.  
      The shank coupling portion  56  corresponds in shape and dimensions to the head coupling portion  28  and is designed to threadingly cooperate therewith. The shank coupling portion  56  has three inner, or “female”, substantially identical, parallel shank threads  64 ′,  64 ″,  64 ′″. The head and shank threads  38 ′,  38 ″,  38 ′″,  64 ′,  64 ″,  64 ′″ are trapezoidal threads. Each of the shank threads  64 ′,  64 ″,  64 ′″ starts at a shank thread start  66 ′,  66 ″,  66 ′″ adjacent the tool shank shoulder  58  and extends rearwardly to terminate in a shank thread end  68 ′,  68 ″,  68 ′″ adjacent the shank coupling rear end  60  (only one shank thread end  68 ′″ is seen in  FIG. 1 ). The shank thread starts  66 ′,  66 ″,  66 ′″ are circumferentially spaced apart from each other by a shank thread start angle σ S  of 120° ( FIG. 3 ).  
      Attention is now drawn to  FIG. 4 . In order to assemble the cutting tool assembly  20 , the cutting-head  22  is brought axially rearwardly towards the tool shank  24  so that the head coupling portion  28  passes through the relief bore  57  and enters the shank coupling portion  56 . The cutting-head  22  is then rotated relative to the tool shank  24  so that the head threads  38 ′,  38 ″,  38 ′″ engage the shank threads  64 ′,  64 ″,  64 ′″. Rotation of the cutting-head  22  continues until the cutting-head shoulder  30  abuts the tool shank shoulder  54 . The abutment between the cutting-head and tool shank shoulders  30 ,  54  provides the cutting-head  22  with axial support.  
      The cutting-head  22  and the tool shank  24  must be coaxially aligned to assure proper functioning of the cutting tool assembly  20 . In the present invention, the coaxial alignment is provided by the threaded coupling of the cutting-head  22  and the tool shank  24 . With the cutting-head  22  and the tool shank  24  threadingly engaged, each of the three shank threads  64 ′,  64 ″,  64 ′″ communicates with a corresponding head thread  38 ′,  38 ″,  38 ′″, to draw the head coupling portion  28  rearwardly into the shank coupling portion  56 . In each cross-section, taken perpendicularly to the tool longitudinal axis T through the threadingly engaged head and shank coupling portions  28 ,  56 , there are three contact regions at which the male and female threads abut. At each contact region, each female thread  64 ′,  64 ″,  64 ′″ exerts a clamping force on the abutting male thread  38 ′,  38 ″,  38 ′″.  
      Due to the trapezoidal shape of the male and female threads  38 ′,  38 ″,  38 ′″,  64 ′,  64 ″,  64 ′″, each clamping force has a centripetal clamping component which extends from the contact region towards the tool longitudinal axis T, in the plane of each cross-section. Therefore, the mutual engagement of the head and the shank threads  38 ′,  38 ″,  38 ′″,  64 ′,  64 ″,  64 ′″ centers the head coupling portion  28  relative to the shank coupling portion  56  at each cross-section, bringing the head and shank longitudinal axes H, S to coaxially align and form the tool longitudinal axis T, and assuring proper functioning of the cutting tool assembly  20 .  
      When the cutting-head  22  is secured to the tool shank  24 , a forward gap  70  exists between the head coupling portion  28  and the cylindrical relief bore  57 , and a rear gap  72  exists between the head coupling rear end  36  and the shank coupling rear end  60 , so that undesired contact between the cutting-head and shank coupling portions, which may adversely affect the axial alignment thereof with the tool longitudinal axis T, is prevented  
      The present invention potentially provides one or more advantages. Included among these may be providing positioning repeatability and coaxial alignment of the cutting-head relative to the shank of the cutting tool assembly, by employing the threaded coupling of the cutting-head and the shank as the centering and coaxial alignment means, thereby simplifying production of the cutting-head and shank.  
      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.