Abstract:
A versatile toolholder system is provided that is used by a numerically controlled machine tool. The toolholder system has an attachment portion that has a standardized shape to allow the toolholder to be used by conventional numerically controlled machine tools. The toolholder is comprised of a toolholder body, a collet adaptor that allows a desired collect to fit into the toolholder body, a pull-up means to pull a collet to fasten the collect in the toolholder body. Various sizes and configurations of collet adaptor can be used to accommodate various collets.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a toolholder for a numerically controlled machine tool, and more particularly, to a versatile toolholder for use with a numerically controlled machine tool that can hold a wide variety of tools by utilizing conventional collets.  
       BACKGROUND OF THE INVENTION  
       [0002]     Numerically controlled machine tools are widely used today for machining works. Typically, a numerically controlled (NC) machine tool includes a wide variety of tools to allow precise machining by automatically controlling an operation of the machining tools and are primarily used for cutting, shaping, milling, turning, boring, drilling, grinding, or polishing of solid parts, such as metals. An example of basic configuration of an NC machine tool is shown a schematic diagram of  FIG. 1 .  
         [0003]     As shown in  FIG. 1 , a typical NC machine tool  20  comprises a bed  12 , with a table  6  which is carried on the bed  12  to be horizontally (X and X directions) and vertically (Z direction) movable on the bed  12 . A work (not shown) to be machined is placed on the table  6  through a fixing means. A tool attachment mechanism (spindle)  8  is positioned over the table  6  for mounting a toolholder that holds a tool appropriate to a current process of machining. A control box  5  includes input means  4  such as a keyboard and a monitor  2  such as a CRT or an LCD display panel. The input means  4  functions as a man-machine interface and allows a user to input instructions and parameters to the NC machine tool  20 . The monitor  2  displays the user&#39;s input data, current operation, various parameters for machining the work, etc.  
         [0004]     An automatic tool exchanging device  10  is provided for automatically changing the tools appropriate for the types of machining process for the tool attachment mechanism  8 . The automatic tool exchanging device  10  generally stores a plurality of tools from which it selects a suitable tool for the current job. The tools in the automatic tool exchanging device  10  are attached to the corresponding toolholders so that the selected tool is attached to the tool attachment mechanism  8  by the tool exchanging device  10 .  
         [0005]     Generally, toolholders to be used for NC machine tools are standardized in outer size and shape at the part which engages with the tool attachment mechanism. Thus, the tools can fit to an automatic tool exchanging device as well as to a tool attachment mechanism regardless of manufacturers or models of NC machine tools. The toolholders for NC machine tools for holding various tools are readily available in the market. One example of such a toolholder is illustrated in a front view of  FIG. 2A .  
         [0006]     A toolholder  30  shown in  FIG. 2A  is comprised of a tool holding portion  34  and an attachment portion  32 . The attachment portion  32  has a hook  36  that will be inserted in the tool attachment mechanism  8 . The attachment portion  32  is standardized so that the toolholder  30  can be used any standard NC machine tools. The tool holding portion  34  holds a tool (not shown), and the attachment portion  32  is fixed to the tool attachment mechanism  8  of the NC machine tool  20 . The tool holding portion  34  is able to hold tools of different sizes and shapes.  
         [0007]     As noted above, the outer shape and size of the attachment portion  32  is standardized to allow the toolholder  30  to be attached to the tool attachment mechanism  8  regardless of the manufacturer or type of the particular NC machine tools. Thus, as long as the toolholder  30  has the standardized shape and size of the attachment portion  32  as shown in  FIG. 2A , the toolholder  30  can be used by different NC machine tools. When a tool is mounted on the tool attachment mechanism  8  through the toolholder  30 , the NC machine tool knows the size and shape of the tool because of the machining program and controls the movement of the tool attachment mechanism (spindle)  8  and the table  6  incorporating the size and shape of the tool.  
         [0008]     The toolholders  30  for NC machine tools described above have drawbacks in that they are generally expensive and can be financially burdensome especially for individual machinists to purchase many toolholders. Moreover, a user must have several different types of toolholders to accommodate various tools used for a project because inner structures of the toolholders are frequently different for accommodate different types of tools. It can be financially burdensome to purchase a new toolholder that is needed for a tool used only for a special project. Even when a machinist has a particular toolholder required for a project, a multiplicity of the same type of such toolholders may be necessary to complete the particular project.  
         [0009]     Many machinists and machine houses generally have various collets that can attach to machine tools other than an NC machine tool. A collet is a type of toolholder for holding tools for traditional machine tool such as a lathe, milling machine, etc. An example of a collet is shown in a front view of  FIG. 2B . Advantages of collets are that collets are relatively less expensive than toolholders used for NC machine tools and collets are readily available in the market. Moreover, because collets are common and traditionally used devices, machinists and machine houses are more likely to have a stock of them.  
         [0010]     Accordingly, there is a need to combine the advantages of a collet used for traditional machining tools and a toolholder used for an NC machine tool, thereby allowing a desired tool to be used by an NC machine tool through a traditional collet without a NC machine toolholder for the particular tool.  
       SUMMARY OF THE INVENTION  
       [0011]     It is, therefore, an object of the present invention to provide a versatile toolholder for a numerically controlled machine tool to use a tool for other machine tool.  
         [0012]     It is another object of the present invention to provide a versatile toolholder for a numerically controlled (NC) machine tool for folding a collet for other machine tool for attachment of a tool to the NC machine tool.  
         [0013]     It is a further object of the present invention to provide a versatile toolholder for an NC machine tool for using a wide variety of tools for traditional machines by the NC machine tool through corresponding collets.  
         [0014]     In one aspect of the present invention, a versatile toolholder for a numerically controlled machine tool is comprised of: a toolholder body having an attachment portion that has a shape that allows the attachment portion to be attached to an attachment mechanism of a numerically controlled machine tool, and a tool holding portion having an inner space for storing a collect therein; a collet adaptor having an inner opening that snugly fits to a tapered portion of the collet, and an outer that snugly fits into a circumferential opening at an end of the toolholding portion of the toolholder body; and a pull-up means to pull the collet toward the inside of the toolholder body to fasten the tapered portion of the collet by the collet adaptor, thereby attaching the collet to the toolholder body; wherein the collet tightly clamps a tool for a traditional machine tool when it is pulled toward the inside of the toolholder body.  
         [0015]     In a further aspect of the present invention, the versatile toolholder for a numerically controlled machine tool further comprises a hook portion that is attached to the end of the attachment portion. The hook portion attached to the end of the attachment portion is inserted in the attachment mechanism of the numerically controlled machine tool when mounting the tool on the numerically controlled machine tool.  
         [0016]     In a further aspect of the present invention, in the versatile toolholder for a numerically controlled machine tool, the attachment portion has a conical shape whose size is standardized to match with attachment mechanisms of numerically controlled machine tools of different makes and types.  
         [0017]     In a further aspect of the present invention, in the versatile toolholder for a numerically controlled machine tool, the toolholder having the collet and the tool clamped by the collet is brought to the attachment mechanism of the numerically controlled machine tool by an automatic tool exchanging device to be mounted on the numerically controlled machine tool.  
         [0018]     In a further aspect of the present invention, in the versatile toolholder for a numerically controlled machine tool, wherein the pull-up means to pull the collet is a screw. The screw to pull the collet has a screw head that is hooked to a stopper wall provided at the inside of the toolholder body to fixate the screw.  
         [0019]     According to the present invention, the toolholder of the present invention has the standard size and shape at the attachment portion thereof while the toolholding portion is designed to accommodate traditional collets of different sizes. Thus, the toolholder of the present invention enables to attach the tool for the conventional machine tool to the NC machine tool through the collet. Since the tools and collets for traditional machine tools are less expensive and wide variety of them are readily available in the market, the toolholder of the present invention enables to use such tools on the NC machine tool at low cost.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a schematic diagram showing an example of basic configuration of a numerically controlled machine tool to apply a toolholder of the present invention.  
         [0021]      FIG. 2A  is a front view showing an example of toolholder used in a numerically controlled machine tool having an attachment portion and a toolholding portion,  FIG. 2B  is a side view showing an example of collet used in a traditional machine tool, and  FIG. 2C  is a front view of the collet of  FIG. 2B .  
         [0022]      FIG. 3A  is a front view of a versatile toolholder of the present invention to be used in a numerically controlled machine tool,  FIG. 3B  is a front view of the versatile toolholder where an inside cross sectional structure is also shown, and  FIG. 3C  is a perspective view of the versatile toolholder in the present invention.  
         [0023]      FIG. 4A  is a left side view of the versatile toolholder in the present invention shown in  FIGS. 3A-3C  to be used in a numerically controlled machine tool, and  FIG. 4B  is a right side view of the versatile toolholder in the present invention.  
         [0024]      FIGS. 5A  to  5 H show collet adapters and collets for use with the toolholder of the present invention.  FIGS. 5A-5C  show relationship between a small collet and a collet adaptor designed for the small collet where  FIG. 5A  is a front view of the collet adaptor,  FIG. 5B  is a side view of the collet adaptor, and  FIG. 5C  is a front view of the small collet.  FIGS. 5D-5F  show relationship between a large collet and a collet adaptor designed for the large collet where  FIG. 5D  is a front view of the collet adaptor,  FIG. 5E  is a side view of the collet adaptor, and  FIG. 5F  is a front view of the large collet.  FIG. 5G  is a front view showing the condition where the collet adaptor and the small collet of  FIGS. 5A-5C  are attached to one another, and  FIG. 5H  is a front view showing the condition where the collet adaptor and the large collet of  FIGS. 5D-5F  are attached to one another.  
         [0025]      FIGS. 6A and 6B  show a hook portion screw to be attached to an end of the versatile toolholder of the present invention where  FIG. 6A  is a front view thereof and  FIG. 6B  is a side view thereof.  
         [0026]      FIGS. 7A and 7B  show a collet screw that is used to pull up a collet inside the versatile toolholder of the present invention where  FIG. 7A  is a front view thereof and  FIG. 7B  is a side view thereof.  
         [0027]      FIGS. 8A-8F  schematically show structural relationships among a collet, a collet adaptor, a toolholder body, a screw for the collet, and a hook portion screw of the toolholder where  FIG. 8A  shows a collet,  FIG. 8B  shows a collet adaptor,  FIG. 8C  shows a cylindrical body of the toolholder body,  FIG. 8D  shows a conical body at the attachment portion of the toolholder body,  FIG. 8E  shows a collet screw, and  FIG. 8F  shows a hook portion screw of the toolholder.  
         [0028]      FIG. 9  is a schematic view showing an assembled condition of the collet, collet adaptor, toolholder body, collet screw, and hook portion screw in the present invention, where structural relationships among these members when assembled in the toolholder are also illustrated.  
         [0029]      FIG. 10  is a schematic view showing an outer appearance of the assembled condition of the collet, collet adaptor, toolholder body, collet screw, and hook portion screw in the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     The present invention will be described in detail with reference to the accompanying drawings. Under the present invention, a versatile toolholder is adaptable to a numerically controlled (NC) machine tool. The versatile toolholder is able to accommodate a collet therein so that a tool attached to the collet can be used by the NC machine tool. In other words, the versatile tool holder of the present invention has the standard size and shape at its outside of the attachment portion for an NC machine tool while having a specific inner structure to install a collet therein. Accordingly, any traditional tool for traditional machine tools for drilling, cutting, etc., that can be clamped by the collet can be used by the NC machine tool. Thus, various tools can be used for the NC machine tool through the traditional collets.  
         [0031]      FIGS. 3A-3C  show the toolholder of the present invention to be used in an NC machine tool through the attachment mechanism  80  of the NC machine tool ( FIG. 1 ). In a front view of  FIG. 3A , a toolholder (toolholder body)  70  in the present invention is conceptually divided into an attachment portion  72  and a holding portion  74 . The attachment portion  72  is a standardized configuration for use in NC machine tools through the attachment mechanism. The holding portion  74  has an inner space to install a selected collet with a collet adaptor therein.  
         [0032]     Since the attachment portion  72  is standardized, the shape and size of the attachment portion  72  is substantially the same as that of the conventional toolholder&#39;s attachment portion shown in  FIG. 2A  except that the attachment portion  72  does not have the hook portion shown in  FIG. 2A . However, a part that is equivalent to the hook portion will be attached when assembling the toolholder as will be described in detail later. In a preferred embodiment, the toolholder  70  is made of aluminum although many other metal material can be used for this purpose.  
         [0033]      FIG. 3B  is a view corresponding to the front view of  FIG. 3A  and further shows a cross sectional inner structure of toolholder. The toolholder  70  has an inner hole extending from the left end of the holding portion  74  to the right end of the attachment portion  72 . The inner hole is to install a traditional collet for a machine tool so that a variety of tools such as a drilling tool, boring tool, etc, can be attached to the NC machine tool.  
         [0034]      FIG. 3C  is a perspective view of the toolholder  70  of the present invention. As shown, the toolholder  70  is configured by an attachment portion  72  having a conical body  112  and the holding portion  74  having a cylindrical body  110  and a circumferential opening  90 . The circumferential opening  90  is provided at the end of the holding portion  74 . As will be explained later in detail, the circumferential opening  90  holds a collet adaptor prepared for the toolholder  70  for tightly attaching the collet clamping a tool.  
         [0035]     Referring back to  FIG. 3B , the toolholder  70  has an inner circular opening from one end to the other end thereof. The toolholder  70  is configured by the attachment portion  72  having the conical body  112  and the holding portion  74  having the cylindrical body  110 . The toolholder  70  has a first circumference opening  90  at the end of the cylindrical body  110 , a first opening end (first step)  92 , a second circumference opening  94 , a second opening end (second step)  96 , a third circumference opening  98 , a third opening end (third step)  100 , a screw opening  102 , a stopper wall  104 , and a screw opening  106 .  
         [0036]     The first circumference opening  90  and the first opening end  92  are used to hold a collet adaptor created for a collet which will be explained in detail with reference to  FIGS. 5A-5F . The second circumference opening  94  and the second opening end  96  serve as a storage space for a collet that clamps a selected tool. The third circumference opening  98 , the third opening end  100 , and the screw opening  102  serve as a hole through which a collet screw (pull-up screw)  190  penetrates to tightly attach the collet in the storage space of the toolholder  70 . The screw opening  106  has thread on its inner wall for attaching a hook portion screw  186  of the toolholder  70  which is required for the standard attachment mechanism of the NC machine tool.  
         [0037]      FIG. 4A  is a side view of the toolholder body  70  as viewed from the holding portion  74 , i.e, the end of the cylindrical body.  FIG. 4B  is a side view of the toolholder body  70  as viewed from the attachment portion  72 , i.e., the end of the conical body. As shown in  FIGS. 4A and 4B , the toolholder body has a substantially tubular shape and holes of different sizes are formed on the same axis from one end to the other end. The numerals for the openings in  FIGS. 4A and 4B  correspond to those in  FIG. 3B .  
         [0038]      FIGS. 5A  to  5 F show collet adapters and their relationship with corresponding collets. The collet adaptor is to match the size of the collet with the first circumference opening  90  of the toolholder  70  of  FIGS. 3A-3C  when the collet with a tool is attached to the toolholder. In other words, the toolholder of the present invention is able to accommodate collets of different sizes with use of corresponding collet adapters. Since the tools and collets for traditional machine tools are less expensive and wide variety of them are readily available in the market, the toolholder of the present invention enables to use such tools on the NC machine tool at low cost.  
         [0039]     The collets of different size and corresponding collet adapters are shown in the drawings. As noted above, collets are used as toolholder for traditional machine tools and collets of various sizes are readily available in the market. Collets are widely used for machine tools other than NC machine tools and are less expensive than the toolholder for NC machine tools. Since the toolholder of the present invention can attach the collets, tools for traditional machine tools can be used for the NC machine tool.  
         [0040]      FIGS. 5A-5C  show the relationship between a collet of relatively small size and a collet adaptor designed for the small collet.  FIG. 5A  is a front view of the collet adaptor,  FIG. 5B  is a side view of the collet adaptor, and  FIG. 5C  is a front view of the small collet.  FIGS. 5D-5F  show the relationship between a collet of relatively large size and a collet adaptor designed for the large collet.  FIG. 5D  is a front view of the collet adaptor,  FIG. 5E  is a side view of the collet adaptor, and  FIG. 5F  is a front view of the large collet.  
         [0041]     A collet adaptor  150  shown in  FIGS. 5A-5B  is designed for a small collet  40  shown in  FIG. 5C . The outer surface of the collet adaptor  150  is designed to fit the first circumferential opening  90  of the toolholder body  70 . The collet  40  has a plurality of slits  46  so that a tool (not shown) can be inserted in a center opening at the left end of the collet  40  in  FIG. 5C . The collet  40  has a tapered portion  44  where the slits  46  are formed, thus, when the tapered portion  44  is tightened, the tool is firmly attached to the collet  40 . The collet  40  also has a screw thread  50  at the right end of  FIG. 5C .  
         [0042]     The collet adaptor  150  of  FIGS. 5A and 5B  has a tapered portion  154  which is designed to snugly fit with the tapered portion  44  of the collet  40 . As will be described later, when the collet  40  is pulled toward the right by fastening a collet screw in the screw thread  50 , the tapered portion  44  of the collet  40  is tightened by the tapered portion  154  of the collet adaptor  150 . Thus, the collet  40  can tightly close the center opening to securely hold the tool (not shown) while being attached to the toolholder  70  for use with an NC machine tool.  
         [0043]     A collet adaptor  160  shown in  FIGS. 5D-5E  is designed for a large collet  170  shown in  FIG. 5F . The outer surface of the collet adaptor  170  is designed to fit the first circumference opening  90  of the toolholder body  70 . Thus, the shape and size of the outer surface of the collet adaptor  150  of FIGS.  5 A-SB and that of the outer surface of the collet adaptor  160  of the collet  170  are identical to one another. The collet  170  of  FIG. 5F  has a plurality of slits  176  so that a tool (not shown) can be inserted in a center opening at the left end of the collet  170  in  FIG. 5F . The collet  170  has a tapered portion  174  where the slits  176  are formed, thus, when the tapered portion  174  is tightened, the tool is firmly attached to the collet  170 . The collet  170  also has a screw thread  52  at the right end of  FIG. 5F .  
         [0044]     The collet adaptor  160  of  FIGS. 5D and 5E  has a tapered portion  164  which is designed to snugly fit with the tapered portion  174  of the collet  170 . As will be described later, when the collet  170  is pulled toward the right by fastening a collet screw in the screw thread  52 , the tapered portion  174  of the collet  170  is tightened by the tapered portion  154  of the collet adaptor  160 . Thus, the collet  170  can tightly close the center opening at the left end to securely hold the tool (not shown) while being attached to the toolholder  70  for use with an NC machine tool.  
         [0045]      FIG. 5G  is a front view showing the condition where the collet adaptor  150  and the small collet  40  of  FIGS. 5A-5C  are attached to one another.  FIG. 5H  is a front view showing the condition where the collet adaptor  160  and the large collet  170  of  FIGS. 5D-5F  are attached to one another. In the condition of  FIG. 5G , the tapered portion  44  of the small collet  40  is snugly fit to the tapered portion  154  of the collet adaptor  150 . In the condition of  FIG. 5H , the tapered portion  174  of the large collet  170  is snugly fit to the tapered portion  164  of the collet adaptor  160 . Such conditions will arise when the collet having a tool is installed and fastened in the toolholder  70  through a collet screw  190  of  FIGS. 7A and 8E .  
         [0046]     Although the above example of the collet adaptor has circular openings to hold a cylindrical collet, the opening of the collet adaptor may take various shapes to accommodate a particular shape and configuration of a collet to be used. Thus, the shape of the opening of the collet adaptor is not limited to a circular opening described in the description and drawings. However, the outer shape of the collet adaptor has to match the inner shape of the first circumference opening  90  of the toolholder body  70 .  
         [0047]      FIGS. 6A and 6B  show a hook portion screw  186  which is inserted in the toolholder body  70 . The hook portion screw is to attach the toolholder body  70  to the NC machine tool through the standard attachment mechanism  8  shown in  FIG. 1 . Thus, the hook portion screw  186  is the same as the hook  36  of the toolholder  30  shown in  FIG. 2A .  FIG. 6A  is a front view showing the shape of the hook screw portion  186 , and  FIG. 6B  is a side view of the hook screw portion  184  as seen from the right end of  FIG. 6A . The hook screw portion  186  is configured by a thread portion  188 , a screw head  184 , and an end portion  187 . The screw portion  188  fits the screw opening  106  of the toolholder body  70 .  
         [0048]     Thus, when the hook screw portion  186  is completely screwed in the toolholder body  70 , the attachment portion  72  will become identical to the attachment portion  32  of the standard toolholder  30  shown in  FIG. 2A . The attachment portion  72  is identical to the standardized shape and size of the toolholder for an NC machine tool. Thus, the toolholder body  70  of the present invention can be used by an NC machine tool while using a tool for a traditional machine tool through a traditional collet.  
         [0049]      FIGS. 7A and 7B  show a collet screw (pull-up screw)  190  which is used for pulling a collet toward the inward of the toolholder  70 . When the collet is pulled in this manner, the opening of the collet having a tool is fastened by the taper portion of the collet adaptor to tightly hold the collet in the toolholder  70 .  FIG. 7A  is a front view showing the pull-up screw  190  configured by a thread portion  194  and a head  192 .  FIG. 7B  is a side view of the pull-up screw  190  as seen from the right end of  FIG. 7A . The thread portion  194  screws in the screw thread  50  or  52  ( FIGS. 5A and 5F ) of the collet.  
         [0050]     When the pull-up screw  190  is fastened in the toolholder  70 , the head portion  192  is fitted to the stopper wall end  104  ( FIG. 3B ). By further screwing the pull-up screw  190 , the collet is moved to the direction of the hook portion screw  186 , i.e, in the direction opposite to the first circumferential opening  90  of the toolholder body  70 . Because of the tapered portions of the collet adaptor and the collet, the slits of the collet are fastened as the collet is pulled by the pull-up screw  190 , thereby fastening the tool in the center opening of the collet. Thus, the collet having the tool is firmly attached to the toolholder  70 .  
         [0051]      FIGS. 8A-8F  schematic diagrams showing as to how the components described above are assembled with one another to form the toolholder of the present invention.  FIG. 8A  shows the collet  70  for clamping a tool,  FIG. 8B  shows the collet adaptor  160  for tightening the collet  170 ,  FIG. 8C  shows a cylindrical body (holding portion  74  shown in  FIG. 3B ) of the toolholder body  70 ,  FIG. 8D  shows a conical body (attachment portion  72  shown in  FIG. 3B ) of the toolholder body  70 ,  FIG. 8E  shows the collet screw (pull-up screw)  190  for pulling the collet  170  toward the inside of the toolholder body  70 , and  FIG. 8F  shows the hook portion screw  186  of the toolholder.  
         [0052]     The tapered portion of the collet  170  of  FIG. 8A  fits to the tapered portion of the collet adaptor  160  of  FIG. 8B  as shown in  FIG. 5H . The outer surface of the collet adaptor  160  fits to the first circumference opening  90  of the toolholder body  70  of  FIG. 8C . The pull-up screw  190  of  FIG. 8E  is inserted from the opening provided at the attachment portion of the toolholder body  70  of  FIG. 8D . The head portion  192  of the pull-up screw  190  is small enough to pass through the opening  106  but is large enough to act as a hook against the end (stopper wall)  104 . Thus, when the pull-up screw  190  is tightened, the collet  170  is pulled toward the inside of the toolholder  70 , thereby fastening the collet  170  by the collet adaptor  160 .  
         [0053]     The hook screw  186  is screwed into the screw opening  106  of the toolholder body  70  of  FIG. 8D  to close the opening  106 . The hook screw  186  forms a hook at the end of the attachment portion  72 , thereby creating the standardized shape of the toolholder for the attachment with the NC machine tool through the attachment mechanism  8  ( FIG. 1 ). Accordingly, the toolholder of the present invention enables to attach the tool for the conventional machine tool to the NC machine tool through the collet.  
         [0054]      FIG. 9  is a partial cross sectional view of the toolholder of the present invention showing the assembled components. The collet  170  is inserted in the collet adaptor  160  as shown in  FIG. 5H  and is inserted in the first circumferential opening  90  at the left end of the toolholder  70 . The collet  170  is pulled by the pull-up screw  190  toward the right, thus, the tool (not shown) at the left end of the collet  170  is tightened by the collet adaptor  160 . As a consequence, the tool (not shown) and the collet  170  clamping the tool are tightly attached to the toolholder  70 . The hook portion screw  186  closes the screw opening  106  at the right end of the toolholder to form the standardized shape and size of the attachment portion  72  of the toolholder  70  for the NC machine tool.  
         [0055]      FIG. 10  is a schematic diagram showing an outer appearance of the toolholder in the present invention when the assembly is completed. The attachment portion  72  is identical to the attachment portion  32  of the conventional toolholder shown in  FIG. 2A . The holding portion  74  has a shape and size different from the toolholder of  FIG. 2A  to accommodate the collet  170  having a tool  78  to use the traditional tool  78  for the ordinary machine tool through the collet.  
         [0056]     According to the present invention, the toolholder of the present invention has the standard size and shape at the attachment portion thereof while the toolholding portion is designed to accommodate traditional collets of different sizes. Thus, the toolholder of the present invention enables to attach the tool for the conventional machine tool to the NC machine tool through the collet. Since the tools and collets for traditional machine tools are less expensive and wide variety of them are readily available in the market, the toolholder of the present invention enables to use such tools on the NC machine tool at low cost.  
         [0057]     Although the invention is described herein with reference to the preferred embodiment, one skilled in the art will readily appreciate that various modifications and variations may be made without departing from the spirit and scope of the present invention. Such modifications and variations are considered to be within the purview and scope of the appended claims and their equivalents.