Abstract:
It is an object of the invention to provide a tap holder in which even when an error is brought about in synchronizing spindle feeding and rotation of a tapper body and a tap collet of a tap holder in correspondence with a machine tool spindle, the synchronization can be established by absorbing the error by a simple constitution. As means therefor, the tap holder is characterized in that a tapper body and a tap collet are inserted by a locking member at portions of the tapper body and the tap collet overlapping each other, and the tap collet is fixed to the tapper body by engaging the locking member with at least one of the tap collet and the tapper body in a state of being interposed with an elastic member on both sides thereof in an axial direction X.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a tap holder for holding a tap for tapping and for equipping with a machine tool spindle. 
     When tapping is carried out by a machine tool by utilizing synchronization with feeding and rotation of a machine tool spindle, rotation and feeding of the machine tool spindle are controlled to synchronize in accordance with a pitch of a tap. However, in actual tapping, owing to a phenomenon referred to as servo delay, an amount of running a tap while machining by rotating becomes larger, or conversely smaller than a tap pitch per rotating the machine tool spindle, tapping is progressed fast or slow by an incoincidence of spindle feeding and rotation, and therefore, a deviation is brought about among an amount of spindle feeding per rotation and a tap pitch. Although in a background art, the incoincidence is prevented by providing floats on both sides in an axial direction of a tap holder, in recent years, the floats are eliminated and the tap holder are an integral structure is constituted by a promotion in an accuracy of synchronizing (synchronizing) spindle rotation and feeding by a development of a mechanism or a control technology. 
     Further, a tap holder deals therewith by being separated into a tapper body and a tap collet to allow a size of a tap by the tap collet. Also a synchronized tap holder constituting an object of complete synchronization is separated into a tapper body and a tap collet and when the tapper body and the tap collet are connected, the tap collet is attached thereto as gapless as possible. 
     However, although a synchronization accuracy of the machine tool is promoted, for example, when a spindle feeding direction and a spindle rotating direction are switched in order to draw a tap from a subject work, rotation of a machine tool spindle does not synchronize with spindle feeding and a small sift of the tap in an axial direction cannot completely be excluded from being brought about, and therefore, there is a drawback of enlarging or leaning a screw thread. 
     As a constitution of absorbing such a synchronization error, there is proposed a constitution in which a tap mounting portion is made to be movable (able to sift) in a rotating axis direction of a spindle by connecting a spindle mounting portion and the tap mounting portion by way of a leaf spring (refer to Patent Reference 1, paragraph No. [0011] shown below), or a constitution in which as in a background art, a tension spring and a compression spring are urged in directions reverse to each other in an axial direction between a spindle and a tap collet and the tap collet is stopped at a position for balancing urge forces, when an error of feeding the spindle is brought about in tapping and a feed amount and a pitch of a tap are incoincident, the spindle is slid slightly in a direction of making the feed amount and the pitch coincident by reacting with an external force from the tap at a front end thereof (refer to Patent Reference 2, paragraph number [0030], FIG. 2 shown below), or a constitution in which a tap driver is provided with a spiral coil having a compressing performance and an extending performance, an attachment body is moved by a small amount in an axis line direction in accordance with a predetermined force exerted to a tap to be able to synchronize (refer to Patent Reference 3, paragraph number [0018], FIG. 2). 
     However, the constitutions described in Patent References 1 through 3 pose a problem that structures are complicated in any of the cases and cost becomes expensive. 
     Further, although Patent Reference 4 shown below describes a tap holding apparatus in which in order to lock a tap to a tap holding shaft, a lock bolt is used, at a position opposed to the lock bolt, an elastically deformable bush is filled between a fixing pin brought into contact with an outer peripheral face of a handle portion and an inner wall of a long hole provided at the tap holding shaft, the fixing pin and a lock ring is made to be pivotable in a circumferential direction relative to the tap holding shaft, and the bush is filled also at a gap between the fixing pin in an axial direction and the inner wall of the long hole (page 8, line 14 through page 9, line 10), such a tap holding apparatus prevents the lock bolt from being loosened by restraining a rotational force and a force in a direction of pressing the tap from being operated to the lock bolt and is not for restraining a synchronization error of spindle feeding and rotation of a spindle. 
     That is, the fixing pin arranged with the bush is brought into contact with an outer peripheral face of the tap operated with a force in an axial direction to lock when the synchronization error of feeding and rotation of the spindle of the machine tool is brought about, and therefore, the force in the axial direction operated to the tap is not sufficiently transmitted to the fixing pin, and even when the elastically deformable bush is arranged on a front side in the direction of pressing the fixing pin, a difference between an amount of moving the top holding shaft and an amount of spontaneously running the tap cannot be absorbed. 
     Further, Patent Reference 5 shown below discloses a tapper mechanism in which a first member and a second member are connected by a connecting pin and an elastic member in a ring-like shape, further, a clutch for reverse rotation and a connecting member (key member) are connected by the connecting pin and the elastic member (refer to paragraph numbers [0009], [0018] FIGS. 3, 7). However, even the elastic member arranged at either of the connecting pins is for alleviating an impact when a clutch for regular rotation is engaged, or for absorbing attachment error of the connecting member and the clutch for reverse rotation, and not for restraining a synchronization error between spindle feeding and rotation of the spindle.
     Patent Reference 1: JP-A-7-60544   Patent Reference 2: JP-A-2004-142033   Patent Reference 3: JP-A-2002-46020   Patent Reference 4: JP-UM-A-59-8725   Patent Reference 5: JP-A-2000-61729   

     SUMMARY OF THE INVENTION 
     The invention has been carried out in consideration of the above-described point and it is an object thereof to provide a tap holder in which in a constitution of separating a tap holder in correspondence with a machine tool spindle to a tapper body and a tap collet, even when an error is brought about in synchronizing feeding and rotation of the machine tool spindle, an error between the tapper body and the tap collet can be absorbed by a simple constitution to synchronize the feeding and the rotation. 
     A tap holder according to the invention is including a tap collet for chucking a tap at one end thereof, and a tapper body for receiving an outer face side of other end of the tap collet in an axial direction to fix unrotatably, and attached to a machine tool having a tap synchronizingly feeding mechanism, and characterized by in which the tap collet and the tapper body are inserted with a locking member at portions of the tap collet and the tapper body overlapping each other, and in which the locking member engages the tap collet and the tapper body in a state of interposing an elastic member on both sides in an axial direction between the locking member and at least one of the tap collet and the tapper body. 
     According to the invention, an error of synchronizing spindle feeding and rotation of a machine tool spindle can be absorbed by a simple constitution by producing a small amount of movement in an axial direction between a tapper body and a tap collet. 
     Further, the tapper body and the tap collet as well as the locking member and the elastic member can be fabricated with high productivity and inexpensively by a simple structure by reducing basic constituent elements. 
     Further, by interchanging the elastic member, a difference in a tap size or a difference in a machined material, wear or an aging change can easily be dealt with. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a tap holder according to a first embodiment of the invention. 
         FIG. 2  is a sectional view enlarging an essential portion of the tap holder according to the first embodiment of the invention. 
         FIG. 3  is a sectional view taken along a line A-A of  FIG. 1 . 
         FIG. 4  is a disassembled view of the tap holder according to the first embodiment of the invention. 
         FIG. 5  is a sectional view enlarging an essential portion of a tap holder according to a modified example of the first embodiment of the invention. 
         FIG. 6  is a sectional view enlarging an essential portion of a tap holder according to a modified example of the first embodiment of the invention. 
         FIG. 7  is a sectional view enlarging an essential portion of a tap holder according to a modified example of the first embodiment of the invention. 
         FIG. 8  is a sectional view enlarging an essential portion of a tap holder according to a second embodiment of the invention. 
         FIG. 9  is a sectional view enlarging an essential portion of a tap holder according to a modified example of the second embodiment of the invention. 
         FIG. 10  is a sectional view enlarging an essential portion of a tap holder according to a modified example of the second embodiment of the invention. 
         FIG. 11  is a sectional view enlarging an essential portion of a tap holder according to a third embodiment of the invention. 
         FIG. 12  is a sectional view enlarging an essential portion of a tap holder according to modified example 1 of the third embodiment of the invention. 
         FIG. 13  is a sectional view taken along a line B-B of  FIG. 12 . 
         FIG. 14  is a sectional view enlarging an essential portion of a tap holder according to modified example 2 of the third embodiment of the invention. 
         FIG. 15  is a sectional view of a tap holder according to modified example 3 of the third embodiment of the invention. 
         FIG. 16  is a sectional view enlarging an essential portion of a tap holder according to modified example 4 of the third embodiment of the invention. 
         FIG. 17  is a sectional view taken along a line C-C of  FIG. 16 . 
         FIG. 18  is a partial sectional view of a tap collet in a state of being inserted with a locking member showing modified example 4 of the third embodiment of the invention. 
         FIG. 19  is a partial sectional view of a tap collet in a state of being inserted with a locking member showing modified example 4 of the third embodiment of the invention. 
         FIG. 20  is a partial sectional view of a tap collet in a state of being inserted with a locking member showing modified example 4 of the third embodiment of the invention. 
         FIG. 21  is a partial sectional view of a tap collet in a state of being inserted with a locking member showing modified example 5 of the third embodiment of the invention. 
         FIG. 22  is a partial sectional view of the tap collet in the state of being inserted with the locking member showing modified example 5 of the third embodiment of the invention. 
         FIG. 23  is a partial sectional view of the tap collet in the state of being inserted with the locking member showing modified example 5 of the third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     A first embodiment of the invention will be explained in reference to the drawings as follows. 
       FIG. 1  is a sectional view of a tap holder  10  according to a first embodiment of the invention,  FIG. 2  is a sectional view enlarging an essential portion of the tap holder  10 ,  FIG. 3  is a sectional view taken along a line A-A of  FIG. 1 , and  FIG. 4  is a disassembled view of the tap holder  10 . 
     The tap holder  10  according to the embodiment is a tap holder for mounting a tap  40  to a machine tool having a tap synchronizingly feeding mechanism, having a tapper body  20  including a shank portion  22  attachably and detachably mounted to a spindle  1  of the machine tool, a tap collet  50  having a tap holding member  42  for holding the tap  40  at a front end thereof, and attachably and detachably attached to the tapper body  20 , and a locking member  70  for connecting the tap collet  50  to the tapper body  20 . 
     The tapper body  20  is provided with an outer cylinder portion  24  integrally with the shank portion  22  at a front end side thereof, the outer cylinder portion  24  is formed with an attaching hollow portion  26  for inserting a shaft portion  52  of the tap collet  50 , and formed with through holes  28 ,  28  penetrated from an outer face of the outer cylinder portion  24  to the attaching hollow portion  26  in a diameter direction of the outer cylinder portion  24 . 
     Further, an inner portion of the tapper body  20  is formed with a flow path  30  for pressurizing a cutting fluid, and the flow path  30  is opened to the attaching hollow portion  26 . 
     The tap collet  50  includes the shaft portion  52  slidingly inserted into an inner peripheral face of the attaching hollow portion  26  of the tapper body  20  in a state of being brought into tight contact therewith, and a flange portion  54  provided at a front end side of the shaft portion  52 . 
     The shaft portion  52  is provided with a through hole  56  penetrated in a diameter direction at a position in correspondence with the through hole  28  provided at the tapper body  20 , the through hole  28  of the tapper body  20  and the through hole  56  of the tap collet  50  are communicated by inserting the shaft portion  52  into the attaching hollow portion  26 , thereby, the locking member  70  is made to be able to be inserted to the outer cylinder portion  24  and the shaft portion  52  at which the tap collet  50  and the tapper body  20  are overlapped. 
     The locking member  70  includes a male screw portion  72 , and a locking shaft portion  74  formed on a front end side of the male screw portion  72  and inserted to the through holes  28  and  56 . A peripheral face of the locking shaft portion  74  is formed with a plurality of first recessed portions  76  in a groove-like shape continuous in a peripheral direction to be spaced apart from each other by predetermined intervals thereamong in an axial direction of the locking shaft portion  74 , and the respective first recessed portions  76  are arranged with elastic members  78  to project from the locking shaft portion  74  to an outer side. The elastic member  78  is a ring-like member formed by a synthetic resin having an elasticity of nylon or the like or rubber and is removably arranged to the locking member  70 . 
     The locking member  70  is fixed to the tapper body  20  by screwing the male screw portion  72  with a female screw portion  32  provided at an inner peripheral face of the through hole  28  in a state of inserting the locking shaft portion  74  to the through hole  28 ,  56 , thereby, the tap collet  50  is engaged with the locking member  70  in a state of interposing the elastic members  78  on both sides in an axial direction of the tap collet  50  indicated by an arrow notation X, and is unrotatably fixed to the tapper body  20 . 
     Further, an end face  52   a  of the shaft portion  52  opposed to a bottom face  26   a  of the attaching hollow portion  26  is arranged with a plurality of resin balls  60  to project from the end face  52   a , and the bottom face  26   a  of the attaching hollow portion  26  and the resin balls  60  are brought into contact with each other. Further, the plurality of resin balls may be constituted by one O ring. 
     As shown by  FIG. 3 , an inner portion of the tap collet  50  is formed with a flow path  62  for pressurizing a cutting fluid, and an outer peripheral face of the shaft portion  52  is provided with an opening portion communicated with the flow path  62 . The outer peripheral face of the shaft portion  52  is arranged with a pair of the O rings  66  by interposing the opening portion, in a state of connecting and fixing the tap collet  50  to the tapper body  20 , the flow path  62  formed at the inner portion of the tap collet  50  is communicated with the flow path  30  formed at the inner portion of the tapper body  20 , and the cutting fluid supplied from a side of the machine tool is pressurized to a blade tip portion of the tap  40  therethrough. 
     A side of the flange  54  of the tapper body  20  is formed with a projection  68  engaged with a key groove  34  formed at an opening edge of the hollow portion  26 , and a rotational shift of the tap collet  50  relative to the tapper body  20  is hampered. 
     As described above, according to the tap holder  10  for the embodiment, the locking shaft portion  74  inserted into the through hole  56  of the tap collet  50  is engaged with the tap collet  50  in the state of interposing the elastic members  78  on both sides in the axial direction of the tap collet  50  indicated by the arrow mark notation X, and therefore, even when a force in either direction of a pressing direction and a pulling direction is generated at the tap collet  50  by the synchronization error of feeding and rotating the spindle  1  of the machine tool, the force is operated to the locking member  74  by way of the elastic member  78 , a difference between an amount of moving the tapper body  20  and an amount of spontaneously running the tap  40  is absorbed by elastically deforming the elastic member  78  and highly accurate tapping can be carried out. 
     Further, the elastic member  78  is arranged to be removably fitted to the first recessed portion  76 , and therefore, when the elastic member  78  is worn to deteriorate, the elastic member  78  can be interchanged by a new one thereof, a high tapping function can be maintained over a long period of time, an easiness of bending of the elastic member  78  can be adjusted by attaching the elastic member  78  having a different hardness to the first recessed portion  76 , and the tap holder  10  suitable for working various kinds of materials can be provided. 
     Further, although according to the embodiment, the elastic members  78  are arranged to all of the plurality of first recessed portions  76  provided at the locking shaft portion  74 , as exemplified in  FIG. 5 , by arranging the elastic members  78  at portions of the first recessed portions  76  and changing a number of the elastic members  78  interposed between the locking shaft portion  74  and the tap collet  50 , the easiness of bending the elastic members  78  can be adjusted, and the tap holder  10  suitable for working various kinds of materials can be provided. 
     Further, although according to the embodiment, the locking shaft portion  74  is provided with the plurality of first recessed portions  76 , and the respective first recessed portions  76  are respectively arranged with single pieces of the elastic members  78 , the invention is not limited thereto but, for example, as shown by  FIG. 6  and  FIG. 7 , a single one of the first recessed portion  76  may be arranged with a plurality of the elastic members  78 . 
     Furthermore, although according to the embodiment, the locking shaft portion  74  is engaged with the tap collet  50  by way of the elastic member  78 , the locking shaft portion  74  may be engaged with the tapper body  20  in a state of interposing the elastic members  78  on both sides in the axial direction indicated by the arrow notation X. 
     Second Embodiment 
     A second embodiment will be explained in reference to  FIG. 8  through  FIG. 10 . Elements the same as or corresponding to those of the first embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 8  through  FIG. 10  are sectional views enlarging an essential portion of the tap holder  10  according to the embodiment. 
     Although according to the first embodiment, the elastic member  78  is arranged at the first recessed portion  76  provided at the locking member  70 , according to the tap holder  10  of the embodiment, an elastic member unit  80  including an elastic member  82  is interposed between the locking shaft portion  74  and the tap collet  50 . 
     Specifically, the elastic member unit  80  includes, for example, a cylinder member  84  in a circular cylindrical shape formed by a material having a rigidity larger than that of the elastic member  82  having a material the same as that of the tap collet  50  and the elastic member  82  arranged at the cylinder member  84  and removably fitted to the through hole  56  provided at the shaft portion  52  of the tap collet  50 , and a hollow portion  88  of the cylinder member  84  is inserted with the locking shaft portion  74  of the locking member  70 . 
     As shown by  FIG. 8  through  FIG. 10 , the elastic member unit  80  may be provided with a plurality of second recessed portions  86  continuous in one peripheral face of the inner peripheral face and an outer peripheral face of the cylinder member  84  or in both of the peripheral faces in a peripheral direction and to be spaced apart from each other by predetermined intervals thereamong in an axial direction, and the second recessed portion  86  may be arranged with the elastic member  82 . 
     As described above, even in the tap holder  10  of the embodiment, by elastically deforming the elastic member  82 , the difference between the amount of moving the tapper body  20  and the amount of spontaneously running the tap  40  can be absorbed and the highly accurate tapping can be carried out. 
     Further, by providing the second recessed portion  86  arranged with the elastic member  82  only at the outer peripheral face of the cylinder member  84 , even when the locking member  70  is drawn or inserted in interchanging the tap collet  50  or the like, the locking shaft portion  74  and the elastic member are not rubbed directly by each other, and therefore, a durability of the elastic member  82  is promoted. 
     Third Embodiment 
     Next, a third embodiment will be explained in reference to  FIG. 11 . Elements the same as or corresponding to those of the first embodiment and the second embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 11  is a sectional view enlarging an essential portion of the tap holder  10  according to the embodiment. 
     A characteristic of the embodiment resides in that the elastic member for absorbing the difference between the amount of moving the tapper body  20  and the amount of spontaneously running the tap  40  is arranged at the tap collet  50 . 
     That is, as shown by  FIG. 11 , the shaft portion  52  of the tap collet  50  is provided with a third recessed portion  90  penetrated in a diameter direction at a position in correspondence with the through hole  28  provided at the tapper body  20 , and by inserting the shaft portion  52  into the attaching hollow portion  26 , the through hole  28  at the tapper body  20  and the third recessed portion  90  at the tap collet  50  are communicated. 
     The third recessed portion  90  formed at the shaft portion  52  is removably fitted with an elastic member  92  in a cylindrical shape formed by a synthetic resin having an elasticity of nylon or the like or rubber, and the elastic member  92  is arranged at the third recessed portion  90  such that a hollow portion  94  of the elastic member  92  is communicated with the through hole  28  formed at the outer cylinder portion  24 . The elastic member  92  is pressed to be fixed by a bolt  96  penetrated from the end face  52   a  of the shaft portion  52  to the third recessed portion  90 . 
     The through hole  28  formed at the outer cylinder portion  24  and the hollow portion  94  of the elastic member  92  are inserted with the locking shaft portion  74  of the locking member  70  in the state of being brought into tight contact therewith, and the locking member  70  is fixed to the tapper body  20  by screwing the male screw portion  72  of the locking member  70  with the female screw portion  32  formed at the inner peripheral face of the through hole  28 . Thereby, the tap collet  50  is engaged with the locking member  70  in the state of interposing the elastic member  92  on the both sides in the axial direction indicated by the arrow mark notation X to be fixed to the tapper body  20  unrotatably. 
     Modified Example 1 of Third Embodiment 
     Modified example 1 of the embodiment will be explained in reference to  FIG. 12  and  FIG. 13 . Elements the same as or corresponding to those of the embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 12  is a sectional view enlarging an essential portion of the tap holder  10  according to the modified example and  FIG. 13  is a sectional view taken along a line B-B of  FIG. 12 . 
     A point of a change from the embodiment resides in that the third recessed portion  90  formed at the shaft portion  52  of the tap collet  50  is not penetrated through the shaft portion  52 . 
     That is, as shown by  FIG. 12  and  FIG. 13 , a plurality (for example, three) of the third recessed portions  90  are arranged in the peripheral direction at equal intervals without penetrating the shaft portion  52  and each of the third recessed portions  90  is fitted with the elastic member  92  in the cylindrical shape. Also a plurality of the through holes  28  are formed at the outer cylinder potion  24  in correspondence with the third recessed portions  90  to be communicated with the hollow portions  94  of the elastic members  92 , and the tap collet  50  is fixed to the tapper body  20  by engaging the tap collet  50  and the locking member  70  by way of the elastic member  92  on the both sides in the axial direction indicated by the arrow mark notation X by inserting the locking shaft portion  74  of the locking member  70  to the through hole  28  and the hollow portion  94  of the elastic member  92 . 
     Modified Example 2 of Third Embodiment 
     Modified example 2 of the embodiment will be explained in reference to  FIG. 14 . Elements the same as or corresponding to those of the embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 14  is a sectional view enlarging an essential portion of the tap holder  10  according to the modified example. 
     As shown by  FIG. 14 , according to a characteristic of the modified example, a side face  92   a  of the elastic member  92  in the cylindrical shape inserted to the third recessed portion  90  formed at the shaft portion  52 , for example, a face thereof brought into contact with an inner wall  90   a  partitioning the third recessed portion  90  is constituted by a recessed and projected face. 
     By providing the side face  92   a  of the elastic member  92  by the recessed and projected face in this way, an easiness of bending the elastic member  92  can easily be adjusted by changing a contact area of the tap collet  50  and the elastic member  92 , and the tap holder  10  suitable for machining various kinds of materials can be provided by only changing the elastic member  92 . Although according to the modified example, the recessed and projected face is provided at the side face  92   a  constituting an outer periphery of the elastic member  92 , otherwise, the recessed and projected face may be provided only at an inner periphery thereof, or the recessed and projected faces may be provided at both side faces. 
     Further, the contact area of the tap collet  50  and the elastic member  92  may be changed by a front side and a rear side of a direction of pressing the tap collet  50 , in other words, by a case of operating a force in a pressing direction to the tap collet  50  and a case of operating a force in a direction of pulling thereto, thereby, the easiness of bending the elastic member  92  can respectively separately be adjusted for the force in the direction of pressing the tap collet  50  and the force in the direction of pulling the tap collet  50 . 
     Modified Example 3 of Third Embodiment 
     Modified example 3 of the embodiment will be explained in reference to  FIG. 15 . Elements the same as or corresponding to those of the embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 15  is a sectional view of the tap holder  10  according to the modified example. 
     A characteristic of the modified example resides in that the elastic member  92  is arranged at the tapper body  20 . 
     That is, as shown by  FIG. 15 , the outer cylinder portion  24  of the tapper body  20  is arranged with a plurality (three in the embodiment) of the third recessed portions  90  in the peripheral direction without penetrating the outer cylinder potion  24 . Each of the third recessed portions  90  is fitted with the elastic member  92  in the cylindrical shape, and the hollow portion  94  of the elastic member  92  is communicated with a stop hole  66  provided at a position in correspondence with each of the third recessed portions  90  at the shaft portion  52  of the tap collet  50 . The tap collet  50  is fixed to the tapper body  20  by engaging the tap collet  50  and the locking member  70  by way of the elastic member  92  on the both sides in the axial direction indicated by the arrow mark notation X by inserting the locking shaft portion  74  of the locking member  70  into the stop hole  66  formed at the shaft portion  52  and the hollow portion  94  of the elastic member  92 . 
     Modified Example 4 of Third Embodiment 
     Modified example 4 of the embodiment will be explained in reference to  FIG. 16  through  FIG. 20 . Elements the same as or corresponding to those of the embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 16  is a sectional view enlarging an essential portion of the tap holder  10  according to the modified example,  FIG. 17  is a sectional view taken along a line C-C of  FIG. 16 , and  FIG. 18  through  FIG. 20  are partial sectional views of the tap collet  50  in the state of being inserted with the locking member  70 . 
     A characteristic of the modified example resides in that a clearance  98  constituting a margin of escaping the deformed elastic member  92  is provided between the elastic member  92  and the locking member  70 . 
     Specifically, as exemplified in  FIG. 16  and  FIG. 17 , the clearance  98  is formed by forming an inner diameter of the hollow portion  94  of the elastic member  92  to be larger than an outer diameter of the locking shaft portion  74  and bending the elastic member  92  by pressing a bolt  96  to an outer peripheral face of the elastic member  92 . 
     The clearance  98  constitutes the margin of escaping the elastic member  92  elastically deformed by the synchronization error of feeding and rotation of the spindle  1  of the machine tool. Therefore, for example, the easiness of bending the elastic member  92  can be adjusted by changing a size of the clearance  98  by changing a size of the hollow portion  94  or the like, and the tap holder  10  suitable for machining various kinds of materials can be provided. 
     Further, the contact area of the locking shaft portion  74  and the elastic member  92  can be made to differ from each other by the case of operating the force in the pressing direction to the tap collet  50  and the case of operating the force in the pulling direction thereto, and the easinesses of bending the elastic member  92  in the respective cases can individually be adjusted. 
     Further, other than the modified example, for example, the clearance  98  may be formed between the locking shaft portion  74  and the elastic member  92  by inserting the elastic member  92  substantially in a shape of a concentric cylinder into the third recessed portion  90  sectional shapes of which are provided in an elliptical shape, a shape of a triangle having rounded corners and the like as shown by  FIG. 18  through  FIG. 20 . In this way, also the sectional shape of the hollow portion  94  can be changed by changing the sectional shape of the third recessed portion  90 , and therefore, the contact area of the locking shaft portion  74  and the elastic member  92  can be changed by the case of operating the force in the pressing direction to the tap collet  50  and the case of operating the force in the pulling direction thereto, and the easinesses of bending the elastic member  92  can separately be adjusted in the respective cases. 
     Modified Example 5 of Third Embodiment 
     Modified example 5 of the embodiment will be explained in reference to  FIG. 21  through  FIG. 23 . Elements the same as or corresponding to those of the embodiment are attached with the same notations and a duplicated explanation thereof will be omitted.  FIG. 21  through  FIG. 23  are partial sectional views of the tap collet  50  in the state of being inserted with the locking member  70 . 
     According to the modified example, as exemplified in  FIG. 21  through  FIG. 23 , the elastic member  92  interposed between the locking shaft portion  74  and the shaft portion  52  of the tap collet  50  on one side in the axial direction indicated by the arrow mark notation X (front side in a direction of pressing the tap collet  50  according to the modified example) is formed to be more thick-walled than the elastic member  92  interposed between the locking shaft portion  74  and the shaft portion  52  of the tap collet  50  on other side (rear side in the direction of pressing the tap collet  50  according to the modified example). Thereby, the easinesses of bending the elastic member  92  can respectively separately be adjusted in the case of operating the force in the pressing direction to the tap collet  50  and the case of operating the force in the pulling direction thereto. 
     Further, although according to the modified example, the elastic member  92  on the front side in the pressing direction of the tap collet  50  is provided to be more thick-walled, the elastic member  92  on the rear side in the pressing direction of the tap collet  50  may be provided to be more thick-walled.