Patent Publication Number: US-2013230361-A1

Title: Rotational locking collet machine tool holder

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a nonprovisional patent application of U.S. Provisional Patent Application No. 61/606,390, filed Mar. 3, 2012, and titled ROTATIONAL LOCKING COLLET MACHINE TOOL HOLDER, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to a machine tool assemblies, and more particularly to a collet chuck machine tool holders for a machine tool spindle. 
     Many milling machines, machining centers, and other machine tools have a machine tool spindle with a tapered recess for receiving a machine tool holder assembly. A conventional machine tool holder assembly includes a tool holder, a cutting tool, a spring collet, and a collet nut. The conventional tool holder, for example a collet chuck such as those available from Techniks, Inc., of Indianapolis, Ind., includes a tapered machine end that couples with the tool spindle tapered recess. The tool holder generally includes a through hole axially formed through the tool holder, both for receiving the spring collet and the cutting tool on the distal chuck end (tool end), and for supplying coolant from the machine tool spindle to the work piece, either through or around the cutting. 
     The distal end of the through hole in the tool holder includes a tapered recess or chuck that is shaped to receive and compress the spring collet. The spring collet includes a through bore that receives the shank of the cutting tool. Tightening of the collet nut onto the distal end of the tool holder axially drives the spring collet deeper into the tapered recess, compressing the spring collet radially, and thus clamping the shank of the cutting tool within the interior bore of the spring collet, fixing the cutting tool within the tool holder. Such collet machine tool assemblies also sometimes include a set screw axially installed in the through hole of the holder, for example, behind the collet. The set screw can be used as a stop to adjust the depth within the through hole to which the cutting tool shank extends, also preventing the cutting tool from translating axially further into the collet chuck during cutting. 
     Although the collet nut and associated tapers of the collet and collet chuck portion of the tool holder do compress and clamp cutting tool within the spring collet, the strength with which the spring collet clamps the cutting tool is sometimes insufficient. The cross sectional shapes of the cutting tool and the through hole of the tool holder are round, so a relative rotation (twist) between the tool holder and the cutting tool may still occur during use. For example, the relatively small diameter of the shank of the cutting tool that is held by the interior bore of the collet may, under sufficient operating torque, lead to the cutting tool shank rotating within the collet. Such rotation can also cause axial pullout of the cutting tool from the tool holder because of the twisting action. 
     Rotational slippage and axial pullout can cause damage to the cutting tool and/or work piece. To avoid rotational slippage and axial pullout, feed rates and RPM must be limited, which is often impractical. Therefore, an improved the conventional machine tool holding assembly that prevents tool rotation is desired. This is also true with collets that are other than the spring type. 
     To overcome the shortcomings, the present invention provides a machine tool holder and assembly to mitigate the aforementioned problems. 
     SUMMARY 
     The present invention may comprise one or more of the features recited in the attached claims, and/or one or more of the following features and combinations thereof. 
     The main objective of the invention is to provide a machine tool holder assembly that prevents a relative rotation between a cutting tool and a tool holder collet. 
     A machine tool assembly has a tool holder, a cutting tool, a collet, and a collet nut. The tool holder defines a keyed recess having multiple corners and/or multiple flats formed around an inner surface of the keyed recess. The keyed recess can be integral with the tool holder or can be a separate positioning chuck rotationally and axially secured within the tool holder. The cutting tool is inserted into the collet and has multiple edges and/or multiple flats formed on a keyed end of shank that are matingly received by the keyed recess to prevent relative rotation between the tool holder and the cutting tool and make the cutting tool rotationally and axial fixed within the tool holder. The keyed recess can include a spacer preventing the keyed end of the cutting tool from contacting a base of the keyed recess, thereby preventing radial misalignment of the cutting with the axis of the tool holder from the axial translation and force applied during tightening of the collet nut and collet. 
     The cutting tool has multiple edges and intervening flats formed on the machine tool end of its shank. When inserted within the collet and into the positioning chuck, the multiple edges of the cutting tool abut with the multiple corners of the keyed recess, which generally can includes the intervening flats on the machine tool end of its shank abutting flats formed between the multiple corners of the keyed recess. Because the cross sectional shape of the keyed recess is multilateral and has multiple corners which the multiple edges abut, the combination of the corners and the edges prevent relative rotation between the tool holder and the cutting tool, whether the keyed end matches the keyed recess, or simply mates with it. Clamping of the collet onto the cutting tool shank centers the cutting tool within the tool holder and prevents axial movement of the cutting tool relative to the tool holder. 
     One illustrative embodiment of a machine tool assembly includes a cylindrical tool holder having a connecting section, a collet section opposite to the connecting section, a flange section located between the connecting section and the collet section, and a through hole formed axially through the connecting section, the flange section and the collet section; a positioning chuck mounted securely in the through hole of the tool holder and having a first end, a second end opposite to the first end of the positioning chuck, an external threaded part formed around the first end of the positioning chuck and screwed in the through hole of the tool holder, and a keyed recess axially formed in the second end of the positioning chuck and having a non-circular cross section, an inner surface. and multiple corners formed around the inner surface of the keyed recess at intervals, a cutting tool inserted into the through hole of the tool holder and having a cutting area located outside the collet section; a keyed end being opposite to the cutting area and having an outer surface and multiple edges which are formed on the outer surface of the keyed end and abut the corners, and a shank formed between the cutting area and the keyed end; and a collet mounted in the through hole of the tool holder at the collet section and mounted securely around the shank of the cutting tool. 
     The machine tool holder can further include a spacer, and a counterbore defined in the center of the base of the keyed recess, the counterbore sized to receive a portion of the length of the spacer. The keyed end of the cutting tool can contact the spacer, thereby preventing the keyed end of the cutting tool from contacting the base of the keyed recess. 
     The keyed end of the cutting tool may have a cross sectional shape the same as that of the keyed recess, and the edges can respectively abut the corners. The positioning chuck can include a coolant hole axially formed through the positioning chuck and communicating with the keyed recess. The cutting tool can include a cutting tool aperture formed through the cutting tool and communicating with the keyed recess. The through hole of the tool holder can have a first segment axially formed through the connecting section and screwed securely on the external threaded part, and a second segment axially formed though the collet section and having a diameter larger than that of the first segment and a bottom, and the tool holder can have an annular abutting surface formed on the bottom of the second segment of the through hole of the tool holder and abutted by the positioning chuck. 
     The cross sectional shape of the keyed end can be rectangular and have four edges correspondingly implemented. Alternatively, the cross sectional shape of the keyed end can be triangular and three edges correspondingly implemented. 
     The positioning chuck can have a coolant hole axially formed through the positioning chuck and communicating with the keyed recess. The cutting tool can have a cutting tool aperture formed through the cutting tool and communicating with the keyed recess. The through hole of the tool holder can have a first segment axially formed through the connecting section and screwed securely on the external threaded part, and a second segment axially formed though the collet section and having a diameter larger than that of the first segment and a bottom, and the tool holder can have an annular abutting surface formed on the bottom of the second segment of the through hole of the tool holder and abutted by the positioning chuck. 
     Additional features of the disclosure will become apparent to those skilled in the art upon consideration of the following detailed description and drawings of the illustrative embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view in partial longitudinal section of a first embodiment of a machine tool assembly in accordance with the present invention; 
         FIG. 2  is an exploded perspective view in partial longitudinal section of the machine tool assembly in  FIG. 1 ; 
         FIG. 3  is a cross sectional side view of the machine tool assembly in  FIG. 1 ; and 
         FIG. 4  is a cross sectional side view of a portion of a second embodiment of a machine tool assembly in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 to 3 , a first illustrative embodiment of a machine tool holder and assembly in accordance with the present invention comprises a tool holder  10 , a positioning chuck  20 , a cutting tool  30  and a collet  40 . 
     The cylindrical tool holder  10  has a main body  11  and a collet nut  12 . The main body  11  has a connecting section  111 , a collet section  112 , a flange section  113 , a though hole  114 , and an abutting surface  115 . The connecting section  111  of the main body  11  is defined at an opposite machine tool end from the collet section  112 . The flange section  113  is located between the connecting section  111  and the collet section  112 . The outer surface  116  of the connecting section  111  is tapered or semi-conical for engagement with a machine spindle (not shown). The collet section  112  is defined at a distal or cutting tool end. The interior surface of the collet section  112  portion of the through hole  114  defines a collet receptacle (chuck)  118  for receiving the collet  40 . With reference to  FIGS. 1 to 3 , the collet  40  is mounted in the through hole  114  at the collet section  112  and is mounted securely around the shank  33  of the cutting tool  30 . The collet  40  may be conventional and requires no modification, for example a standard sealed or unsealed spring collet. 
     The hole  114  is optionally a through hole that provides not only the collet receptacle  118 , but also a coolant flow path from the machine spindle (not shown) to the collet  40  and/or the cutting tool  30 . In the illustrated embodiment, the through hole  114  is axially formed through the connecting section  111 , the flange section  113 , and the collet section  112 . 
     The through hole  114  in the illustrative embodiment includes a first segment  1141  and a second segment  1142 . The first segment  1141  is axially formed through the connecting section  111 . The second segment  1142  is axially formed though the collet section  112  and has a diameter larger than that of the first segment  1141 . An annular abutting surface  115  is formed on the bottom of the second segment  1142  of the through hole  114 , at the intersection with the first segment  1141 . 
     The collet nut  12  is mounted on a distal end of the collet section  112 . As the collet nut  12  is tightened onto the tool holder body  11 , is translates the collet  40  axially toward the connecting section  111 , deeper into the tapered collet receptacle  118 , thereby partially radially collapsing the collet, radially compressing the interior bore  42  onto the shank  33  of the cutting tool  30 , thereby securing the cutting tool relative to the tool holder  10 . As the interior bore  42  compresses onto the shank  33  and the collet nut  12  is further tightened, the tool  30 , including the shank  33  may also translate deeper into the tool holder body  11 . Further features of the tool holder  10 , except various features of the through hole  114  and keyed recess  22 , may be conventional and a further detailed description is therefore omitted. 
     The positioning chuck  20  is mounted securely in the through hole  114  of the tool holder  10 . A shoulder  24  is defined between a first end  26  and a second end  28  of the positioning chuck  20 . The shoulder  24  of the chuck  20  can abut the abutting surface  115 , thereby securing the positioning chuck  20  rotationally and axially relative to the tool holder body  11 . 
     The positioning chuck  20  may be similar to prior art set screws used to limit axial depth of the cutting tool shank  33  in the tool holder body  11 ; however, a keyed recess  22  is axially formed in the second end  28  of the positioning chuck  20 . The keyed recess  22  has an inner surface defining multiple corners (or points)  221  and/or interleaving multiple flats  222 , each at intervals around the interior circumference of the keyed recess, and thus the keyed recess  22  has a non-circular cross-section. The multiple corners  221  and multiple flats  222 , collectively (whether one or both are present) referred to as a keyed recess, are axially aligned with the through hole  114 . The positioning chuck  20  can also include a coolant hole  23  axially formed through the positioning chuck  20  and communicating with the keyed recess  22 , thus allowing for liquid coolant flow from the machine spindle (not shown) to the cutting tool  30 . 
     An external thread  21  is formed around the first end  26  of the chuck  20  and is screwed into a matching threaded portion of the first segment  1141  of the through hole  114 . The external thread  21  must be oriented so that position chuck  20  will tighten and not loosen during cutting. Because machine tool spindles typically rotate clockwise, the external thread  21  and associated matching threaded portion of the first segment are typically right-hand threads (which is opposite of that typically used for prior art set screws). The chuck  20  can be rotated so that external threads  21  engage with the threaded portion of the first segment  1141  until shoulder  24  contacts annular abutting surface  115 , effectively securing the chuck  20  rotationally and axially relative to the through hole  114  and tool holder body  11 . 
     With reference to  FIGS. 1 to 3 , the cutting tool  30  is mounted securely in tool holder  10 , extending through the collet nut  12 , into the through hole  114 , and includes a cutting end  31 , a shank  33 , and a keyed end  32  defined at an end of the shank  33  opposite the cutting end. Features related to keyed end  32  are sometimes referred to as the driving end or tang on tapping tools. When assembled with the tool holder  10 , the cutting end  31  is located outside the collet section  112  and the keyed end  32  and at least a portion of the shank  33 , is located within the tool holder  10 . In the illustrative embodiment, the cutting tool  30  with the special features of the keyed end  32  is a milling cutter, in this example, a milling cutter having an indexable insert, for example, an end mill. 
     The keyed end  32  has an outer surface defining multiple edges (or points)  321  and/or interleaving multiple flats  322 , each at intervals around its periphery. The edges  321  can be formed by having a tool shank  33  having a single diameter and forming flats  322  around the circumference of the shank adjacent the keyed end  32 . The multiple edges  321  and multiple flats  322 , collectively (whether one or both are present) referred to as the keyed end, are axially aligned with the shank  33 . The keyed recess  22  in positioning chuck  20  is sized and the multiple corners  221  and/or flats  222  formed to receive the keyed end  32  such that the edges  321  abut the corners  221 , and/or the flats  322  abut the flats  222 , thus prevented relative rotation of the positioning chuck  20  and the cutting tool  30 . Additionally or alternatively, surfaces between the edges  321  of keyed end  32  and surfaces between corners  221  of keyed recess  22  are cooperatively adjacently positioned to prevent relative rotation. Specifically, depending to the relative cross-sections and fit, the engagement of the keyed end  32  into the keyed recess  22  may impede all relative rotation, or may allow only partial rotation before abutting of the edges  321  and corners  221  and/or associated flats  322  and  222  prevents further rotation. The surfaces between edges  321  and corners  221  may be, but are not required to be planar surfaces, so long as the cooperation of features of the keyed recess  22  and keyed end  32  prevent all relative or at least continuing rotation. 
     The keyed end  32  can have a cross-sectional shape the same as that of the keyed recess  22 , so the edges  321  respectively abut the corners  221 . For example, the cross sectional shape of the keyed end  32  can be rectangular and four edges  221 . Alternatively, the cross-sectional shape of the fixing segment  1141  may be different from that of the keyed end  32 . For example, the cross-sectional shape of the fixing segment  1141  can be hexagonal and the cross sectional shape of the keyed end  32  can be triangular. The present invention does not limit the cross sectional shapes of the keyed end  32  and the keyed recess  22  as a number of geometrically differing, but engage cross sections are known in the art that prevent continuing rotation of the cutting tool relative to the keyed recess  22  and thus the machine tool body  11 . In the illustrative embodiment, the keyed recess  22  and keyed end  32  each have four matching corners (or points)  221  and  321  formed by interleaving matching flats  222  and  322 ; however, other numbers of corners and or flats, or other shapes and features, for example, as are known in the fastening and driving art, can be used, as long as the coupling of the keyed recess  22  and keyed end  32  prevents relative rotation of the cutting tool  30  about the machine tool body  11 . 
     Because cross sectional shape of the keyed recess  22  of the positioning chuck  20  is multilateral and has multiple corners  221  which the edges  321  of the cutting tool  30  abut, the combination of the corners  221  and the edges  321  and/or the flats  222  and  322  prevent relative rotation between the tool holder  10  and the cutting tool  30 , making the cutting tool  30  securely rotationally fixed with the tool holder  10  and thus preventing rotational slippage, axial pullout, and related problems. 
     As shown in  FIG. 3 , the cutting tool  30  can have a coolant aperture  34  formed through the cutting tool  30  and communicating with the keyed recess  22 . Accordingly, coolant supplied by the machine spindle (not shown) can flow through the coolant hole  23  in the positioning chuck  20  and through the cutting tool aperture  34  in the cutting tool  30 , to cool the cutting tool  30  and a work piece. 
     Referring to  FIG. 3 , optionally, in the illustrative embodiment, a spacer  29  is positioned between the end of the keyed end  32  of the cutting tool  30  and the base  223  of the keyed recess  22 . The spacer  29  prevents the end of the keyed end  32  of the cutting tool  30  from contacting the base  223  of the keyed recess  22 , and is made from a slightly axially compressible material, for example, a length of poly tubing, for example, but not limited to, polyethylene, polypropylene, or polyurethane tubing. If keyed end  32  were to contact the base  223  during the tightening of the collet nut  12  on the collet  40  and onto the shank  33  of the tool  30 , as the collet  40  is further tightened, the resulting axial translation of tool  30  toward the base  223  can induce axial misalignment of the cutting tool  30  with the tool holder  10 , the shank  33  being radially off of machine center, cutting run out, vibration, and/or excessive tool cutter wear. The spacer serves to initially axially position the keyed end of the cutting tool distal enough from the base so as to prevent the keyed end from contacting the base of the keyed recess as the cutting tool translates toward the base during tightening of the collet nut. 
     In the illustrative embodiment, the spacer  29  is received by a counterbore  25  formed in the center of the base  223  of the keyed recess  22 . The counterbore  25  can be sized in depth to receive a portion of the length of the spacer  29  and can be sized in diameter to receive the spacer  29 . For example, the diameter of the counterbore  25  can be a press fit or other fit so that spacer  29  is retained in counterbore  25  once inserted into the counterbore, and a length of the spacer  29  that prevents the cutting tool  30  from contacting the base  223  can extend outside of counterbore  25 , for example, at least about  0 . 010  inches. 
     For example, the length of spacer  29  extending from the counterbore  25  and the material selected for spacer  29  should allow some compression, and resistant excess compression that would allow the cutting tool  30  to contact base  223 . Specifically, preventing contact of cutting tool  30  and base  223  upon the collet  40  and collet nut  12  being loosely assembled to the tool holder  10 , the cutting tool  30  inserted within the collet  40  so that the keyed end  32  extends into the keyed recess  22  and into contact with the spacer  29 , and the collet nut  12  tightened sufficiently on the collet  30  and cutting tool shank  33  to perform cutting, for example, torque to about 140 ft/lbs. 
     Using tubing as the material for spacer  29 , or otherwise providing an axial coolant passage though the spacer, provides the added benefit of allowing the coolant or other fluid to be transmitted from coolant hole  23  in the positioning chuck  20  to the coolant aperture  34  in the cutting tool  30 . Because the spacer  29  will slightly compress between the cutting tool  30  and positioning chuck  20  as the collet nut  12  is tightened, axially translating the cutting tool  30  toward base  115 , for example, about 0.003 to about 0.009 inches, the opposite ends of the spacer  29  will form a seal between coolant hole  23  and coolant aperture  34 . This seal prevents fluid from escaping into the spaces between the features of the keyed end  32  and the keyed recess  22  and from flowing on around the shank  33  and toward the collet  40 . This added advantage of fluid sealing may allow the use of a standard non-sealed collet  40 , rather than a standard steel sealed or other type of sealed collet that would otherwise be required to ensure fluid is transmitted through the aperture  34  in the cutting tool  30 , rather than through the collet. 
     Alternatively, the base  223  of the keyed recess can provide a stop surface, whether compressible or not compressible, that prevents axial translation of the cutting tool  30  toward the connecting section  111  (machine spindle end), thus fixing the cutting tool axial relative to the machine tool holder body  11 . 
     Referring to  FIG. 4 , a portion of a second illustrative embodiment of the machine tool holder  10 ′ is shown to illustrate an alternative feature of the keyed recess  22 . Specifically, rather than the keyed recess  22  being formed in a separate positioning chuck  20  as discussed above, the keyed recess  22  can be integral with the tool holder  10 ′. More specifically, the keyed recess  22  can be formed by the tool holder body  11  along a portion of the through hole  114 , and/or the keyed recess  22  can be in communication with the collet receptacle  118 . Further features of keyed recess  22  discussed herein can similarly be defined integrally by the tool holder body  11 , including the multiple corners  221 , flats  222 , bottom  223 , counterbore  25 , and cooling hole  23 . 
     While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit and scope of the invention as defined in the claims and summary are desired to be protected.