Description

AN EXTENSION MECHANISM OF THE SPINDLE MEMBER

FOR THE MACHINE TOOL

Technical Field

[1] The present invention relates to an extension mechanism for attachment to a spindle member of a machine tool, and more particularly, to such an extension mechanism for attachment to a spindle member of a machine tool that can extend a spindle member in accordance with the shape of a workpiece or the surrounding conditions. Background Art

[2] Generally, machine tools are used to machine a workpiece to a predetermined shape, and have been disclosed in Korean Patent Laid-Open Publication Nos. 1998-0060780, 2006-0076885, and 2002-0049242. Further, the machine tools have been widely used in a variety of industrial fields, and an example of the prior art machine tools will be described below.

[3] FIG.1 is a schematic longitudinal, partial cross-sectional view showing a conventional machine tool. As shown in FIG.l, a conventional machine tool 10 includes a body 12, a spindle member 20 rotatably disposed at the body 12 by means of bearings, rotating means 30 disposed at the lower side of the body 12 so as to rotate the spindle member 20, advancing and retracting means 40 disposed at the rear side of the spindle member 20, and a tool-fixing part 50 mounted at the front end portion of the spindle member 20 so as to couple a tool for machining a workpiece thereto, the tool-fixing part 50 having a key k formed protrudedly on the rear surface thereof.

[4] In this case, the spindle member 20 includes: a cylindrical spindle 21 having a first through-hole 22 formed therein and a key indentation h formed at one side of the front end surface thereof so as to insert the key k of the tool-fixing part 50 thereto, the first through-hole 22 having a first large diameter portion 23, a small diameter portion 26 and a second large diameter portion 27 which are sequentially formed along the inner periphery thereof, the first large diameter portion being formed in a tapered shape in which the diameter thereof is gradually decreased in a direction from the front free end side to the rear end side and having a first annular groove 24 and a first annular projection 25 formed sequentially along the rear end periphery thereof; a push rod 28 mounted in the first through-hole 22 of the spindle 21 so as to detachably mount the tool-fixing part 50 thereto; a first collet chuck 29 mounted at one end thereof to the front end portion of the push rod 28 and engaged at the other end thereof with first annular groove 24 of the first large diameter portion 23 so as to allow the tool-fixing part 50 to be detachably mounted thereto; and a spring S disposed between the inner

periphery of the second large diameter portion 27 and the outer periphery of the push rod 28 so as to apply an elastic force to the push rod 28.

[5] The advancing and retracting means 40 is a hydraulic cylinder operated such that when a hydraulic pressure is introduced to a first inlet hole 42, the protruding portion formed along the rear end of the push rod 28 is pushed toward the front end portion of the spindle 21, and when the hydraulic pressure is introduced to a second inlet hole 44, the push rod 28 is pulled. When the advancing and retracting means 40 pulls the push rod 28, the first collet chuck 29 constrains the tool-fixing part 50 so as to mount the tool-fixing part 50 thereto. Contrarily, when the advancing and retracting means 40 pushes the push rod 28, the first collet chuck 29 releases the tool-fixing part 50 from the constrained state thereof so as to demount the tool-fixing part 50 therefrom.

[6] An operation for detachably mounting the tool-fixing part 50 to the conventional machine tool 10 as constructed above will be described with reference to a partially enlarged view of the machine tool in FIG.l. FIGs.2a and 2b are enlarged cross- sectional views showing the portion 'A' depicted by a circular dotted line in the conventional machine tool of FIG.l, wherein the operations for mounting the tool-fixing part 50 to the machine tool 10 are illustrated.

[7] Referring to FIG.2a, first, the first collet chuck 29 coupled to the front end portion of the push rod 28 is disposed along the first annular groove 24 formed along the first large diameter portion 23 of the spindle 21, at a state of being slightly widened at the distal end portion thereof. In this case, the push rod 28 is in a state of being slid forwardly by means of the advancing and retracting means 40.

[8] Referring next to FIG.2b, when the advancing and retracting means 40 is operated to allow the push rod 28 to be slid backwardly after the tool-fixing part 50 is inserted into the first large diameter portion 23 of the spindle 21, the first collet chuck 29 coupled to the front end portion of the push rod 28 is slid backwardly together with the push rod 28, and then, the first collet chuck 29 becomes narrow at the end portion thereof by means of the first annular projection 25 formed along the first large diameter portion 23 to constrain the tool-fixing part 50 thereon, thereby completing the mounting of the tool-fixing part 50 to the machine tool. At this time, of course, the key k of the tool- fixing part 50 is coupled to the key indentation h formed at one side of the front end surface of the spindle 21.

[9] Therefore, the machine tool 10 is configured such that the first collet chuck 29 coupled to the front end portion of the push rod 28 serves to mount the tool-fixing part 50 thereon, and the tool-fixing part 50 mounted to the first large diameter portion 23 of the spindle 21 of the spindle member 20 is rotated by means of the rotating means 30, thereby conducting the machining on the workpiece.

[10] As mentioned above, the conventional machine tool 10 has an advantage in that the

tool-fixing part 50 is mounted thereto or demounted therefrom easily by means of the advancing and retracting movements of the push rod 28, but it has some shortcomings in that since the spindle member 20 itself is limited in length, the body 12 may not approach a workpiece because of the shape of the workpiece or the surrounding conditions, which makes it difficulty to machine the workpiece. Therefore, there is an urgent need for an extension mechanism for attachment to the spindle member that can extend the spindle member 20 to which the tool-fixing part 50 is mounted. Disclosure of Invention Technical Problem

[11] Accordingly, the present invention has been made in an effort to solve the above problems occurring in the prior arts, and it is an object of the present invention to provide an extension mechanism for attachment to a spindle member of a machine tool that can easily extend a spindle member in accordance with the shape of a workpiece or the surrounding conditions, exhibits an excellent coupling force with the spindle member to stably machine the workpiece, thereby improving a working efficiency, and can allow a tool-fixing part to be mounted thereto or demounted therefrom in an automatic manner. Technical Solution

[12] To achieve the above object, there is provided an extension mechanism for attachment to a spindle member of a machine tool including: a rotary body formed entirely in a generally cylindrical shape and formed at the rear end portion thereof in a conical shape which is gradually decreased in diameter as it goes toward a distal end thereof, the cylindrical rotary body including: a flange part formed outwardly from the outer periphery at one side thereof, the flange part having a plurality of bolt-holes formed circumferentially thereon; a key indentation formed at one side of the front end surface thereof; and a through-hole formed therein and having a large diameter portion and a mounting groove having different diameters from each other in such a manner as to be spaced apart from each other by a predetermined distance, the large diameter portion having an annular groove and an annular projection formed sequentially along the rear end periphery thereof; and an operating rod member disposed inside the through-hole of the cylindrical rotary body in such a manner as to detachably mount a tool-fixing part at the front end portion thereof and to be coupled to the spindle member at the rear end portion thereof so as to be operated in cooperation with the spindle member.

[13] According to the present invention, preferably, the operating rod member includes: an operating rod having a retaining projection protruded outwardly from the outer periphery of the middle portion thereof so as to be fittingly seated in the mounting

groove of the cylindrical rotary body and a head portion disposed at the rear end portion thereof in such as manner as to be protruded outwardly from the through-hole of the rotary body so as to be coupled to the spindle member; a spring interposed between the retaining projection of the operating rod and the mounting groove of the cylindrical rotary body so as to provide an elastic force therebetween, thereby allowing the operating rod to be brought into closer contact with the inner periphery of the through-hole of the cylindrical rotary body; and a collet chuck coupled to the front end periphery of the operating rod in such a manner as to be disposed at the end portion thereof along the annular groove of the through-hole, thereby detachably mounting the tool-fixing part thereonto.

[14] According to the present invention, preferably, an extension mechanism for attachment to a spindle member of a machine tool further includes a guide means adapted to support the outer periphery of the cylindrical rotary body, thereby preventing the vibrations of the cylindrical rotary body, without giving any interference during the rotating operation thereof.

[15] According to the present invention, preferably, the guide means includes: a housing insertedly fit around the outer periphery of the cylindrical rotary body so as to be coupled to the machine tool at the rear end periphery thereof; and a plurality of bearings interposed between the inner periphery of the housing and the outer periphery of the cylindrical rotary body.

[16] According to the present invention, preferably, the guide means includes: a bracket having a vertical face member insertedly fit around the outer periphery of the cylindrical rotary body so as to support the front end periphery of the cylindrical rotary body and a horizontal face member extending backwardly from the vertical face member in such a manner as to be coupled to the machine tool; and a plurality of bearings interposed between the vertical face member of the bracket and the outer periphery of the cylindrical rotary body.

Advantageous Effects

[17] According to the present invention, there is provided an extension mechanism for attachment of a spindle member of a machine includes the cylindrical rotary body and the operating rod member mounted inside the cylindrical rotary body in a relatively simple structure, such that it almost does not cause any trouble during the operation, and if the extension of the spindle member is needed in accordance with the shape of the workpiece or the surrounding conditions, the spindle member can be easily extended by the bolt-coupling of the cylindrical rotary body to the spindle of the spindle member, which gives an excellent coupling force between the extension mechanism and the spindle member, thereby conducting the stable machining for the

workpiece and achieving a high working efficiency.

[18] Furthermore, in case where the push rod of the machine tool is moved forwardly and backwardly, it is slid together with the operating rod member of the spindle member extension mechanism, which allows the tool-fixing part to be detachably mounted automatically on the operating rod member, thereby improving the convenience in use. Brief Description of Drawings

[19] FIG.1 is a schematic cross-sectional view showing a conventional machine tool.

[20] FIGs.2a and 2b are enlarged cross-sectional views showing the portion 'A'depicted by a circular dotted line in the conventional machine tool of FIG.l, wherein the operations for mounting the tool-fixing part 50 onto the machine tool are illustrated.

[21] FIG.3 is a perspective view showing an extension mechanism for attachment to a spindle member of a machine tool according to a preferred embodiment of the present invention.

[22] FIG.4 is a longitudinal sectional view showing a cylindrical rotary body in the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[23] FIG.5 is a perspective view showing an operating rod member in the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[24] FIG.6 is a schematic assembled longitudinal sectional view showing the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[25] FIGs.7a and 7b are schematic cross-sectional views showing the use states of the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[26] FIGs.8a and 8b are schematic cross-sectional views showing the operations of the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[27] FIGs.9a and 9b are schematic cross-sectional views showing the examples of guide means in the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention. Best Mode for Carrying out the Invention

[28] Hereinafter, an explanation on an extension mechanism for attachment to a spindle member of a machine tool according to a preferred embodiment of the present invention will be given with reference to the attached drawings, wherein in the description of the present invention, the parts corresponding to those of the conventional practices are indicated by corresponding terms and reference numerals.

[29] FIG.3 is a perspective view showing an extension mechanism for attachment to a spindle member of a machine tool according to a preferred embodiment of the present invention, FIG.4 is a longitudinal sectional view showing a cylindrical rotary body in the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention, FIG.5 is a perspective view showing an operating rod member in the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention, and FIG.6 is a schematic assembled longitudinal sectional view showing the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[30] Referring to FIGs.3 to 5, an extension mechanism 100 for attachment to a spindle member of a machine tool according to a preferred embodiment of the present invention includes a rotary body 110 and an operating rod member 120.

[31] As shown in FIGs.3 and 4, first, the rotary body 110 is formed entirely in a generally cylindrical shape and formed at the rear end portion thereof in a conical shape which is gradually decreased in diameter as it goes toward a distal end thereof, the cylindrical rotary body 110 including: a flange part 117 formed outwardly from the outer periphery at one side thereof and having a plurality of bolt-holes 118 formed circum- ferentially thereon; a key indentation 119 formed at one side of the front end surface thereof; and a through-hole 112 formed therein and having a large diameter portion 113 and a mounting groove 116 having different diameters from each other in such a manner as to be spaced apart from each other by a predetermined distance, the large diameter portion 112 having an annular groove 114 and an annular projection 115 formed sequentially along the rear end periphery thereof.

[32] In this case, the aim of forming the rear end portion of the cylindrical rotary body

110 in the conical shape is to enable the conical shaped rear end portion of the cylindrical rotary body to be coupled to the first large diameter portion 23 of the spindle 21 of the spindle member 20 of the machine tool 10, and the large diameter portion 113 of the through-hole 112 formed in the cylindrical rotary body 110 has a tapered shape in which the diameter thereof is gradually decreased in a direction from the front free end side to the rear end side, that is, the same shape as that of the first large diameter portion 23 of the spindle 21 so as to insert the tool-fixing part 50 thereto.

[33] Further, the aim of forming the flange part 117 having the bolt-holes 118 formed cir- cumferentially thereon at one side of the rear end portion thereof is to enable the flange part to be coupled to the spindle 21 of the spindle member 20 by means of bolts B, and the aim of forming the key indentation 119 at one side of the front end surface of the cylindrical rotary body 110 is to enable the key k formed on the tool-fixing part 50 to

be coupled thereto.

[34] On the other hand, the rotary body 110 is formed of a unitary body in the preferred embodiment of the present invention, but it may be implemented such that two parts are bolt-coupled to each other by the formation of the flanges on the coupled portions thereof so as to achieve easy coupling of the operating rod member 120 and easy maintenance thereof.

[35] Next, as shown in FIG.5, the operating rod member 120 includes an operating rod

122, a spring 125, and a collet chuck 126.

[36] First, the operating rod 122 is formed entirely in an elongated, bar-like shape, having a retaining projection 123 protruded outwardly from the outer periphery of the middle portion thereof so as to be fittingly seated in the mounting groove 116 of the rotary body 110 and a head portion 124 disposed at the rear end portion thereof so as to be coupled to the spindle member 20.

[37] Next, the spring 125 is interposed between the retaining projection 123 of the operating rod 122 and the mounting groove 116 of the rotary body 110 so as to provide an elastic force therebetween, such that the operating rod 122 is brought into closer contact with the inner periphery of the through-hole 112 of the rotary body 110.

[38] Then, the collet chuck 126 is coupled to the front end periphery of the operating rod

122 in such a manner as to be seated at the end portion thereof along the annular groove 114 of the through-hole 112, thereby allowing the tool-fixing part 50 to be detachably mounted thereto.

[39] The collet chuck 126 has been already explained when the spindle member 20 is di scussed, and since it is well known to those skilled in the art, the detailed construction and operation thereof will be omitted. Hereinafter, however, the construction and operation of the collet chuck 126 will be described briefly.

[40] That is, the collet chuck 126 includes a body 126a coupled to the operating rod 122, a plurality of blade portions 126b formed circularly at the outside of the front end periphery of the body 126a, and a band 126c adapted to provide an elastic force in such a manner as to allow the ends of the blade portions 126b to be widened toward the outside.

[41] On the other hand, the collet chuck 126 has been proposed in a variety of shapes, and hence, it will be clearly apparent that the collet chucks having another shape also fall into the scope of the present invention, as long as they implement the same operations as in the present invention.

[42] Now, the coupling relation between the rotary body 110 and the operating rod member 120 will be explained with reference to FIG.6.

[43] The operating rod member 120 is provided inside the through-hole 112 formed along the inner periphery of the rotary body 110. At this time, the head portion 124 formed at

the rear end periphery of the operating rod 122 of the operating rod member 120 is protruded outwardly from the through-hole 112 of the rotary body 110, and the retaining projection 123 formed outwardly from the middle portion of the operating rod 122 is disposed into the mounting groove 116 formed in the through-hole 112 in such a manner as to be pushedly mounted at the rear end of the mounting groove 116 by means of the elastic force of the spring 125 disposed between the retaining projection 123 and the mounting groove 116. The opened end portions of the collet chuck 126 coupled to the front end portion of the operating rod 122 are disposed along the annular projection 115 formed in the through-hole 112, thereby maintaining slightly narrow state.

[44] On the other hand, since the operating rod 122 is moved to the rear end portion of the rotary body 110 by means of the elastic force of the spring 125, the opened end portions of the collet chuck 126 coupled to the front end portion of the operating rod 122 are disposed along the annular projection 115, thereby maintaining slightly narrow state, but if the operating rod member 120 is coupled to the spindle member 20, the operating rod 122 is moved to the front end portion of the rotary body 110, such that the opened end portions of the collet chuck 126 are disposed inside the annular groove 114, thereby maintaining an opened state to insert the tool-fixing part 50 thereto.

[45] FIGs.7a and 7b are schematic cross-sectional views showing the use states of the extension mechanism for attachment to the spindle member of a machine tool according to the preferred embodiment of the present invention, and FIGs.8a and 8b are schematic cross-sectional views showing the operations of the extension mechanism for attachment to a spindle member of a machine tool according to the preferred embodiment of the present invention.

[46] Referring to FIG.7a, first, the cross-section of the front end portion of the machine tool 10 is partially illustrated. Here, the machine tool 10 as mentioned above includes: the body 12; the spindle member 20 rotatably disposed at the body 12 by means of bearings; the rotating means 30 disposed at the lower side of the body 12 so as to rotate the spindle member 20; the advancing and retracting means 40 disposed at the rear side of the spindle member 20; and the tool-fixing part 50 mounted at the front end portion of the spindle member 20 so as to couple a tool for machining a workpiece thereto. In this figure, only a portion of the body 12 and the spindle member 20 is illustrated. At this time, the spindle 21 of the spindle member 20 has a plurality of bolt-holes 118a formed circumferentially on the front end surface thereof in such a manner as to be coupled to the extension mechanism 100 for attachment to the spindle member.

[47] As mentioned in the conventional machine tool, the spindle 21 has the first through- hole 22 formed along the inner periphery thereof and having the first large diameter portion 23, the first annular groove 24 and the first annular projection 25, and the push

rod 28 mounted along the inner periphery of the through-hole 22 is coupled at the front end portion thereof to the first collet chuck 29. In this case, the end portions of the first collet chuck 29 are disposed along the first annular groove 24, thereby maintaining a slightly outwardly widened state.

[48] It should be appreciated that in the state where the outwardly opened state of the end portions of the first collet chuck 29 is maintained, the push rod 28 is moved forwardly by means of the advancing and retracting means 40 which is not shown.

[49] On the other hand, the machine tool 10 has been explained in the description on the conventional practices, and hence, the coupling relation of the machine tool 10 with the extension mechanism 100 for attachment to a spindle member of a machine tool according to the present invention will be described hereinafter.

[50] The extension mechanism 100 for attachment to the spindle member according to the present invention is coupled to the spindle member 20 of the existing machine tool 10 as constructed above. As shown in FIG.7b, that is, after the conical-shaped rear end portion of the rotary body 110 is inserted into the first large diameter portion 23 formed inside the spindle 21, the bolt-holes 118 formed on the flange part 117 formed along the outer periphery of the rotary body 110 are coupled correspondingly to the bolt-holes 118a formed on the front end surface of the spindle 21 by means of the bolts B, thereby rigidly fixing the rotary body 110 to the spindle 21.

[51] The rear end portion of the operating rod 122 provided along the through-hole 112 of the rotary body 110, that is, the head portion 124 comes into close contact with the top surface of the first collet chuck 29 coupled to the front end portion of the push rod 28, such that the retaining projection 123 of the operating rod 122 slightly contracts the spring 125 disposed inside the mounting groove 116, thereby slightly pushing the operating rod 122 toward the front end portion of the rotary body 110. Thus, the end portions of the collet chuck 126 coupled to the front end portion of the operating rod 122, that is, the ends of the blade portions 126b are moved into the annular groove 114 formed in the through-hole 112 of the rotary body 110 and are slightly opened by means of the elastic force of the band 126c so as to mount the tool-fixing part 50 thereto.

[52] Therefore, the extension mechanism 100 for attachment to the spindle member according to the present invention serves to extend the spindle member 20 of the machine tool 10, while being ready to mount the tool-fixing part 50 for machining the workpiece.

[53] Now, an operation of the extension mechanism 100 for attachment to the spindle member of a machine tool according to the present invention will be explained hereinafter.

[54] Referring to FIG.8a, after the general tool- fixing part 50 is inserted into the large

diameter portion 113 formed along the front end portion of the through-hole 112 of the rotary body 110, the push rod 28 of the spindle member 20 is slid backwardly by using the advancing and retracting means 40 of the machine tool 10. At this time, the key k formed on the tool-fixing part 50 is inserted into the key indentation 119 formed on the front end surface of the rotary body 110.

[55] As shown in FIG.8b, next, the end portions of the first collet chuck 29 coupled to the front end periphery of the push rod 28 are disposed along the first annular projection 25 and constrains the head portion 124 of the operating rod 122, such that the first collet chuck 29 is slid backwardly together with the head portion 124. Thus, the collet chuck 126 coupled to the front end periphery of the operating rod 122 is also slid backwardly, while the end portions of the blade portions 126b are being narrow by means of the annular projection 115 formed inside the through-hole 112, such that a head 52 of the tool-fixing part 50 inserted into the large diameter portion 113 is constrained and mounted thereto. At this time, the collet chuck 126 can hold the mounted tool- fixing part 50 more rigidly by means of the expansion force of the spring 125 disposed in the mounting groove 116 formed inside the through-hole 112.

[56] Although not shown, the operations opposite to the mounting operations are conducted so as to release the tool-fixing part 50 from its constrained state and to demount the tool-fixing part 50 from the collet chuck 126 of the operating rod 122. In other words, when the push rod 28 of the machine tool 10 is slid forwardly, the operating rod 122 coupled to the push rod 28 is also slid forwardly, and thus, the end portions of the blade portions 126b of the collet chuck 126 are disposed into the annular groove 114 formed inside the through-hole 112, thereby maintaining an outwardly opened state. As a result, the tool-fixing part 50 is released from its constrained state and is easily demounted from the collet chuck 126 of the operating rod 122.

[57] Like this, the extension mechanism 100 for attachment to the spindle member according to the present invention is mounted on the machine tool 10, and after the tool-fixing part 50 is mounted on the extension mechanism 100 if the spindle 21 is rotated by using the rotating means 30 of the machine tool 10, the extension mechanism 100 for attachment to the spindle member having the rotary body 110 coupled to the spindle 21 and the operating rod member 120 coupled to the push rod 28 is rotated together with the tool-fixing part 50 mounted on the collet chuck 126 of the operating rod member 120 and coupled to the key indentation 119 of the rotary body 110 through the key k, thereby conducting the machining on the workpiece.

[58] FIGs.9a and 9b are schematic cross-sectional views showing guide means in the extension mechanism 100 for attachment to the spindle member of a machine tool according to the preferred embodiment of the present invention.

[59] First, even in case where the length of the extension mechanism 100 for attachment to the spindle member is relatively short, it does not matter, but in case where it is relatively long, vibrations, that is, movements may be generated during the machining of the workpiece. Therefore, the extension mechanism 100 for attachment to the spindle member of the present invention further includes guide means 130 adapted to support the extension mechanism 100 for attachment to the spindle member, without giving any interference during the rotating operation thereof.

[60] The guide means 130 may be formed in a variety of shapes, and in the preferred embodiment of the present invention, the guide means 130 having two shapes will be explained.

[61] Referring first to FIG.9a, the guide means 130 includes a housing 132 insertedly fit around the outer periphery of the cylindrical rotary body 110 so as to be coupled to the machine tool 10 at the rear end periphery thereof by means of bolts B and bearings 134 interposed between the inner periphery of the housing 132 and the outer periphery of the rotary body 110. As a result, the housing 132 coupled to the body 12 of the machine tool 10 by means of the bolts B serves to support the rotary body 110 of the extension mechanism 100 for attachment to the spindle member through the bearings 134, thereby preventing the rotary body 110 from being vibrated and at the same time giving no interference during the rotating operation of the rotary body 110, such that the rotary body 110 is more stably rotated by the formation of the guide means 130.

[62] Referring next to FIG.9b showing another example of the guide means 130, the guide means 130 includes a bracket 136 having a vertical face member insertedly fit around the outer periphery of the rotary body 110 so as to support the front end periphery of the rotary body 110 and a horizontal face member extending backwardly from the vertical face member in such a manner as to be coupled to the machine tool 10 by means of bolts B; and bearings 138 interposed between the vertical face member of the bracket 136 and the outer periphery of the rotary body 110. As a result, the bracket 136 coupled to the body 12 of the machine tool 10 by means of the bolts B serves to support the front end periphery of the rotary body 110 of the extension mechanism 100 for attachment to the spindle member through the bearings 138, thereby preventing the rotary body 110 from being vibrated and at the same time giving no interference during the rotating operation of the rotary body 110, such that the rotary body 110 is more stably rotated by the formation of the guide means 130.

[63] According to the present invention, therefore, the extension mechanism 100 for attachment to the spindle member of the machine tool includes the rotary body 110 and the operating rod member 120 mounted inside the rotary body 110 in a relatively simple structure, it almost does not cause the trouble during the operation, and if the extension of the spindle member 20 is needed in accordance with the shape of the

workpiece or the surrounding conditions, the spindle member 20 can be easily extended by the bolt-coupling of the rotary body 110 to the spindle 21 of the spindle member 20, which gives an excellent coupling force between the extension mechanism 100, thereby conducting the stable machining on the workpiece and achieving a high working efficiency.

[64] Furthermore, when the push rod 28 of the machine tool 10 is moved forwardly and backwardly, it is slid together with the operating rod member 120 of the extension mechanism 100, which allows the tool-fixing part 50 to be detachably mounted automatically on the operating rod member 120, thereby improving the convenience in the use.

[65] Moreover, although the length of the extension mechanism 100 is relatively long, the guide means 130 is further provided to prevent the movements of the extension mechanism 100, thereby advantageously achieving more stable operations.

[66] While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.