Patent Publication Number: US-2003228199-A1

Title: Tool holder

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a tool holder to be attached to a spindle of a machine tool. More particularly, the invention relates to a tool holder which allows adjustment of its rotational weight balance associated with rotation about its axis.  
       [0003] 2. Description of the Related Art  
       [0004] When a machine tool such as a machining center is used to cut a workpiece by means of a cutting tool such as a drill or an end mill, vibration of a tool holder including the cutting tool has an adverse effect on accuracy in machining the workpiece. A cause for this vibration is forced vibration induced by rotational imbalance of the tool holder.  
       [0005] A conventional tool holder which allows adjustment of its rotational imbalance is disclosed, for example, in Japanese Utility Model Registration No. 2512454.  
       [0006]FIGS. 1 and 2 show a conventional tool holder having such a balance adjustment mechanism. A tool holder  1  includes a tapered shank portion  2  to be attached to an unillustrated spindle of a machine tool; a flange portion  3  formed at a large-diameter end of the shank portion  2  and serving as a grip; and an arbor  4  formed integrally and coaxially on a side of the flange portion  3  opposite the shank portion  2 . A cutting tool (not shown) such as a drill is attached to an end portion of the arbor  4  by means of an unillustrated collet chuck.  
       [0007] A plurality of threaded holes  5  are formed at predetermined circumferential intervals on an end surface  3   a  of the flange portion  3  located on the side toward the arbor  4 . An adjustment weight(s)  6  is removably screwed into an appropriate threaded hole(s)  5  for adjusting dynamic weight balance of the tool holder  1  associated with rotation of the tool holder  1  about its axis.  
       [0008] However, in the conventional tool holder  1 , an adjustment weight(s)  6  is attached to the flange portion  3  such that the screw-type adjustment weight(s)  6  is merely screwed into a relevant threaded hole(s)  5  of the flange portion  3 . When vibration induced by high-speed rotation or vibration induced by machining is exerted on the tool holder  1 , the tool holder  1  potentially involves a problem such that the adjustment weight(s)  6  is loosened and comes out of the threaded hole(s)  5  with long-term use.  
       SUMMARY OF THE INVENTION  
       [0009] An object of the present invention is to provide a tool holder which allows reliable, low-cost implementation of coming-out prevention means for preventing detachment of a weight balance adjustment member.  
       [0010] According to a tool holder of the present invention, a weight balance adjustment member removably screwed into a threaded hole is prevented from coming out of the threaded hole by coming-out prevention means. Thus, detachment of the weight balance adjustment member can be reliably prevented, and the lock mechanism can be implemented at low cost.  
       [0011] According to a tool holder of the present invention, a plurality of threaded holes are formed at predetermined circumferential intervals on the outer circumferential surface of a flange portion in such a manner as to extend radially to a predetermined depth; balance adjustment members of the same length and the same mass are previously screwed into the threaded holes; and the adjustment member(s) is moved radially so as to adjust the tool holder to a condition free from rotational imbalance. Thus, there is no need to prepare various kinds of adjustment members of different lengths and masses, thereby facilitating storage management of adjustment members.  
       [0012] In the tool holder of the present invention, a detachment prevention member is provided on the outer circumferential surface of the flange portion, thereby preventing potential detachment of balance adjustment members from the threaded holes during use of the tool holder. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013] Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiments when considered in connection with the accompanying drawings, in which:  
     [0014]FIG. 1 is a partially sectional side view showing a conventional tool holder;  
     [0015]FIG. 2 is an end view viewed along line  2 - 2  of FIG. 1;  
     [0016]FIG. 3 is a longitudinal, partially sectional view of a tool holder having coming-out prevention means according to one embodiment of the present invention;  
     [0017]FIG. 4 is an end view viewed along line  4 - 4  of FIG. 3;  
     [0018]FIG. 5 is an enlarged sectional view of an adjustment member and a threaded hole portion in the embodiment of FIG. 3;  
     [0019]FIG. 6 is an enlarged sectional view of an adjustment member and a threaded hole portion in another embodiment of the present invention;  
     [0020]FIG. 7 is a side view of the adjustment member of FIG. 6;  
     [0021]FIG. 8 is an end view viewed along line  8 - 8  of FIG. 7;  
     [0022]FIG. 9 is a front view of an adjustment member in still another embodiment of the present invention;  
     [0023]FIG. 10 is a right-hand side view of the adjustment member of FIG. 9;  
     [0024]FIG. 11 is an explanatory view showing another manner of attachment in which the adjustment member having coming-out prevention means according to the present invention is attached to a flange portion of a tool holder;  
     [0025]FIG. 12 is an explanatory view showing still another manner of attachment in which the adjustment member having coming-out prevention means according to the present invention is attached to a connecting, stepped portion of a tool holder;  
     [0026]FIG. 13 is an explanatory view showing still another manner of attachment in which the adjustment member having coming-out prevention means according to the present invention is attached to a connecting, stepped portion of a tool holder;  
     [0027]FIG. 14 is a partially sectional side view of a tool holder according to still another embodiment of the present invention;  
     [0028]FIG. 15 is a side view of the adjustment member shown in FIG. 14;  
     [0029]FIG. 16 is an end view viewed along line  16 - 16  of FIG. 15; and  
     [0030]FIG. 17 is a perspective view of a detachment prevention member for preventing detachment of the adjustment members shown in FIG. 14. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0031] Embodiments of the present invention will next be described in detail with reference to the drawings.  
     [0032]FIG. 3 is a longitudinal, partially sectional view of a tool holder having coming-out prevention means according to one embodiment of the present invention; FIG. 4 is an end view viewed along line  4 - 4  of FIG. 3; and FIG. 5 is an enlarged sectional view showing an adjustment member and a threaded hole portion in the present embodiment.  
     [0033] As shown in FIG. 3, a tool holder  10  includes a holder body  14  which in turn includes a tapered shank portion  11  to be attached to an unillustrated spindle of a machine tool; a flange portion  12  formed at a large-diameter end of the shank portion  11  and serving as a grip; and an arbor  13  (which serves as a tool attachment portion) formed integrally and coaxially on a side of the flange portion  12  opposite the shank portion  11 . A cutting tool  16  such as a drill is attached to an end portion of the arbor  13  by means of a collet chuck  15 .  
     [0034] As shown in FIGS. 3 and 4, a plurality of threaded holes  17  are formed at predetermined circumferential intervals on an end surface  12   a  of the flange portion  12  located on the side toward the arbor  13 . The threaded holes  17  extend in parallel with the axis of the holder body  14  and assume a predetermined depth. Screw-type adjustment members  18  are removably screwed into selected appropriate threaded holes  17  so as to adjust rotational weight balance of the tool holder  10  associated with rotation of the tool holder  10  about its axis. Each of the adjustment members  18  has coming-out prevention means  19  for preventing the same from coming out of the threaded hole  17 .  
     [0035] Various kinds of adjustment members  18  of different lengths and the same diameter are prepared such that weight differs slightly thereamong.  
     [0036] As shown in FIGS. 4 and 5, the lock mechanism  19  includes a ring member  191  such as an O-ring, and a stepped portion  192 . The ring member  191  is provided on the inner circumferential surface of the threaded hole  17  in such a manner as to partially project toward the center of the threaded hole  17 . The ring member  191  is formed from, for example, synthetic resin and is elastically deformable. The stepped portion  192  is formed on the outer circumferential surface of one end portion of the adjustment member  18 . When the adjustment member  18  is screwed into the threaded hole  17 , the stepped portion  192  is engaged with the ring member  191  so as to prevent detachment of the adjustment member  18 .  
     [0037] A tool engagement hole  18   a  is formed on an end surface of the adjustment member  18  located opposite a leading end of the adjustment member  18  to be screwed into the threaded hole  18 . The tool engagement hole  18   a  receives a tool for rotating the adjustment member  18  for attachment or detachment of the same.  
     [0038] In adjustment of the tool holder  10  of the above-described structure for rotational imbalance, the tool holder  10  is subjected to a balance test on a balancing machine. When any imbalance is involved, the balancing machine displays factors associated with the imbalance; specifically, excess mass, radius, and angle with respect to a reference position. On the basis of these values, the mass and attachment direction of the adjustment member(s)  18  are determined so as to correct the imbalance.  
     [0039] Then, the adjustment member(s)  18  of the above-obtained mass is selected and screwed into the threaded hole(s)  17  corresponding to the above-obtained direction. Since the stepped portion  192  of the adjustment member  18  screwed into the threaded hole  17  is engaged with the ring member  191  as shown in FIG. 5, the adjustment member  18  can be prevented from coming out of the threaded hole  17 .  
     [0040] As described above, the tool holder  10  of the present embodiment is configured such that the stepped portion  192  of the adjustment member  18  screwed into the threaded hole  17  of the holder body  14  is engaged with the ring member  191  provided on the inner circumferential surface of the threaded hole  17  so as to prevent the adjustment member  18  from coming out of the threaded hole  17 . Thus, even when vibration induced by high-speed rotation or vibration induced by machining is exerted on the holder body  14 , the adjustment member  18  can be reliably prevented from coming out of the threaded hole  17 . Prevention of detachment of the adjustment member  18  is implemented merely through provision of the ring member  191  such as an O-ring on the inner circumferential surface of the threaded hole  17  and thus can be implemented at low cost.  
     [0041] Next, coming-out prevention means for preventing detachment of an adjustment member from a tool holder according to another embodiment of the present invention will be described with reference to FIGS.  6  to  8 .  
     [0042]FIG. 6 is an enlarged sectional view of an adjustment member and a threaded hole portion in the present embodiment; FIG. 7 is a side view of the adjustment member of FIG. 6; and FIG. 8 is an end view of the adjustment member of FIG. 7.  
     [0043] The adjustment member and the threaded hole portion shown in FIG. 6 will be described below, while structural features similar to those of FIG. 3 are denoted by common reference numerals. Threaded holes  17  similar to those of FIG. 3 are formed on the end surface  12   a  of the flange portion  12  located on the side toward the arbor  13 . A screw-type adjustment member(s)  20  is removably screwed into a selected appropriate threaded hole(s)  17  so as to adjust rotational weight balance of the tool holder  10  associated with rotation of the tool holder  10 . The adjustment member  20  has coming-out prevention means  21  for preventing the same from coming out of the threaded hole  17 .  
     [0044] Various kinds of adjustment members  20  of different lengths and the same diameter are prepared such that weight differs slightly thereamong.  
     [0045] As shown in FIGS.  6  to  8 , the lock mechanism  21  includes a plurality of elastic portions (in the present embodiment, four elastic portions)  211  formed on one end portion (a leading end portion to be screwed into the threaded hole  17 ) of the adjustment member  20 . Specifically, a cross slit  20   a  is formed on the leading end surface of the adjustment member  20  in such a manner as to extend axially, thereby dividing the leading end portion of the adjustment member  20  into the elastic portions  211  along the circumferential direction. As shown in FIG. 7, the elastic portions  211  are radially spread beyond the diameter of the threaded hole  17 .  
     [0046] A tool engagement hole  20   b  is formed on an end surface of the adjustment member  20  located opposite the leading end of the adjustment member  20  to be screwed into the threaded hole  17 . The tool engagement hole  20   b  receives a tool for rotating the adjustment member  20  for attachment or detachment of the same.  
     [0047] When rotational weight balance of the tool holder  10  is to be adjusted by use of the adjustment member  20  having the lock mechanism  21 , as in the case of the embodiment of FIG. 3, the tool holder  10  is subjected to a balance test on a balancing machine. When any imbalance is involved, on the basis of factors associated with the imbalance; specifically, excess mass, radius, and angle with respect to a reference position, the mass and attachment direction of the adjustment member(s)  20  are determined so as to correct the imbalance. Then, the adjustment member(s)  20  of the thus-obtained mass is selected, and is screwed into the threaded hole(s)  17  corresponding to the thus-obtained direction in such a manner that the lock mechanism  21  serves as a leading end for screwing. As a result of the screw engagement, the elastic portions  211  which are radially spread as shown in FIG. 7 are elastically squeezed radially inward to thereby come into close contact with the inner circumferential surface of the threaded hole  17 .  
     [0048] Thus, according to the tool holder of the present embodiment, even when vibration induced by high-speed rotation or vibration induced by machining is exerted on the holder body, the adjustment member  20  can be reliably prevented from coming out of the threaded hole  17 . Since the lock mechanism  21  for preventing detachment of the adjustment member  20  is formed such that the cross slit  20   a  is formed on one end surface of the adjustment member  20  to thereby divide the end portion into a plurality of elastic portions  211  along the circumferential direction, prevention of detachment of the adjustment member  20  can be implemented at low cost.  
     [0049] Next, coming-out prevention means for preventing detachment of an adjustment member from a tool holder according to still another embodiment of the present invention will be described with reference to FIGS. 9 and 10.  
     [0050]FIG. 9 is a front view of an adjustment member in the present embodiment; and FIG. 10 is a right-hand side view of the adjustment member of FIG. 9.  
     [0051] According to the present embodiment, coming-out prevention means  23  of an adjustment member  22  for adjusting weight balance of a tool holder includes a thin film layer  231  shown in FIGS. 9 and 10. The thin film layer  231  is formed in the following manner. Synthetic resin is applied to the outer circumferential surface of the screw-type adjustment member  22  in such a manner as to assume the form of a strip extending in parallel with the axis of the adjustment member  22 . When the adjustment member  22  is screwed into a threaded hole, the thin film layer  231  partially fills the gap between the threaded hole and the adjustment member  22 , thereby restraining rotation of the adjustment member  22 .  
     [0052] Thus, according to the tool holder of the present embodiment, even when vibration induced by high-speed rotation or vibration induced by machining is exerted on the holder body, the adjustment member  22  can be reliably prevented from coming out of the threaded hole. Since the thin film layer  231  which partially constitutes the lock mechanism  23  can be formed merely through application of synthetic resin in the form of a strip to the outer circumferential surface of the adjustment member  22 , prevention of detachment of the adjustment member  22  can be implemented at lower cost.  
     [0053] With regard to attachment of the adjustment member(s)  18  having coming-out prevention means to the flange portion  12 , the present invention is not limited to that of FIG. 3 in which the adjustment member  18  extends in parallel with the axis of the arbor  13 .  
     [0054] For example, attachment of the adjustment member(s)  18  may be as shown in FIG. 11. Specifically, threaded holes  17 A are formed on the end surface  12   a  of the flange portion  12  in such a manner as to extend along respective directions that intersect with the axis of the arbor  13  at an acute angle. The adjustment member(s)  18  having the lock mechanism  19  is removably screwed into an appropriate threaded hole(s)  17 A. Such attachment of the adjustment member(s)  18  yields action and effect similar to those which the embodiment of FIG. 3 yields.  
     [0055] In FIG. 11, structural features similar to those of FIG. 3 are denoted by common reference numerals.  
     [0056] With regard to attachment of the adjustment member(s)  18  having coming-out prevention means to the holder body  14 , the present invention is not limited to that of FIG. 3 in which the adjustment member(s)  18  is attached to the flange portion  12 .  
     [0057] For example, attachment of the adjustment member(s)  18  may be as shown in FIG. 12. Specifically, a plurality of threaded holes  17 B are formed at predetermined circumferential intervals on the outer circumferential surface of a connecting, stepped portion  24  which connects the flange portion  12  and the arbor  13 , in such a manner as to radially extend. The adjustment member(s)  18  having the lock mechanism  19  is removably screwed into an appropriate threaded hole(s)  17 B. Such attachment of the adjustment member(s)  18  yields action and effect similar to those which the embodiment of FIG. 3 yields.  
     [0058] In FIG. 12, structural features similar to those of FIG. 3 are denoted by common reference numerals.  
     [0059] Alternatively, the adjustment member(s)  18  may be attached as shown in FIG. 13. An edge part of the connecting, stepped portion  24  which connects the flange portion  12  and the arbor  13  is obliquely cut off so as to form an inclined end surface  241 . A plurality of threaded holes  17 C are formed on the inclined end surface  241  in such a manner as to extend along respective directions that intersect with the axis of the connecting, stepped portion  24  at an acute angle and to be arranged at predetermined intervals on the same circle whose center is located on the axis of the connecting, stepped portion  24 . The adjustment member(s)  18  having the lock mechanism  19  is removably screwed into an appropriate threaded hole(s)  17 C. Such attachment of the adjustment member(s)  18  yields action and effect similar to those which the embodiment of FIG. 3 yields.  
     [0060] In FIG. 13, structural features similar to those of FIG. 3 are denoted by common reference numerals.  
     [0061] Next, a tool holder according to still another embodiment of the present invention will be described with reference to FIGS.  14  to  17 .  
     [0062]FIG. 14 is a partially sectional side view of the tool holder according to the present embodiment; FIG. 15 is a side view of the adjustment member shown in FIG. 14; FIG. 16 is an end view viewed along line  16 - 16  of FIG. 15; and FIG. 17 is a perspective view showing a detachment prevention member for preventing detachment of the adjustment members shown in FIG. 14.  
     [0063] In FIG. 14 showing a tool holder  10 , structural features similar to those of FIG. 3 are denoted by common reference numerals, and repeated description thereof is omitted. Description below focuses on structural features that differ from those of FIG. 3.  
     [0064] The tool holder  10  of FIG. 14 differs from that of FIG. 3 in the following: a plurality of threaded holes  26  are formed at predetermined circumferential intervals on the outer circumferential surface of a flange portion  12  in such a manner as to extend radially to a predetermined depth; and balance adjustment members  27  which are sufficiently shorter than the depth of the threaded holes  26  are screwed into the threaded holes  26  such that position thereof is adjustable along a radial direction of the flange portion  12 . The adjustment members  27  are adapted to adjust rotational weight balance of the holder body, and each have coming-out prevention means  28  for preventing the same from coming out of the corresponding threaded hole  26 .  
     [0065] Notably, the adjustment members  27  used in the present embodiment assume the same length and the same mass.  
     [0066] As shown in FIGS. 15 and 16, the lock mechanism  28  includes an insert member  283  and a plurality of elastic portions  281  formed through circumferentially dividing one end portion of the adjustment member  27 . The insert member  283  is made of a metal material resembling a round bar or an elastic metal material and is fitted into a gap  282  between the elastic portions  281  so as to spread the elastic portions  281  beyond the diameter of the threaded hole  26 .  
     [0067] As shown in FIG. 14, a detachment prevention member  29  for preventing detachment of the adjustment members  27  from the threaded holes  26  is provided on the outer circumferential surface of the flange portion  12  where the threaded holes  26  are formed.  
     [0068] As shown in FIG. 17, the detachment prevention member  29  is formed in the following manner: a narrow metal plate material is formed into the shape of a ring which fits the outside diameter of the flange portion  12 . Tool insertion holes  291  are formed in the detachment prevention member  29  at positions which face the corresponding threaded holes  26 , in order to allow insertion of a tool  30  for adjusting the position of the adjustment member  27  screwed in the threaded hole  26 , along a radial direction of the flange portion  12 . The detachment prevention member  29  is fixedly attached to the outer circumference of the flange portion  12  by means of clamp screws  31  inserted through respective mounting holes  292  which are formed at opposite end portions of the detachment prevention member  29 .  
     [0069] In adjustment of the tool holder  10  of the above-described structure for rotational imbalance, the adjustment members  27  each having the lock mechanism  28  are screwed into the threaded holes  26 , for example, in such a manner as to reach the respective bottoms of the threaded holes  26 . Furthermore, the detachment prevention member  29  is fixedly attached to the flange portion  12 . In this state, as in the case of the embodiment of FIG. 3, the tool holder  10  is subjected to a balance test on a balancing machine. When any imbalance is involved, on the basis of factors associated with the imbalance; specifically, excess mass, radius, and angle with respect to a reference position, the mass and attachment direction of the adjustment member(s)  27  are determined so as to correct the imbalance. The adjustment member(s)  27  corresponding to the thus-obtained direction is rotated so as to be moved in a radial direction of the flange portion  12 , by use of the tool  30  inserted through the corresponding tool insertion hole  291  of the detachment prevention member  29 , whereby the tool holder  10  is adjusted to a condition free from rotational imbalance.  
     [0070] Thus, according to the tool holder  10  of the present embodiment, even when vibration induced by high-speed rotation or vibration induced by machining is exerted on the holder body  14 , the adjustment members  27  can be reliably prevented from coming out of the threaded holes  26 . Since the insert member  283  and the elastic portions  281  formed at one end portion of the adjustment member  27  constitute the lock mechanism  28 , prevention of detachment of the adjustment members  22  can be implemented at lower cost.  
     [0071] According to the present embodiment, the adjustment members  27  of the same length and the same mass are previously screwed into the threaded holes  26 , and the adjustment member(s) is moved radially so as to adjust the tool holder  10  to a condition free from rotational imbalance. Thus, there is no need to prepare various kinds of adjustment members  27  of different lengths and masses, thereby facilitating storage management of the adjustment members  27 .  
     [0072] According to the present embodiment, the detachment prevention member  29  is provided on the outer circumferential surface of the flange portion  12 , thereby preventing potential detachment of the adjustment members  27  screwed into the threaded holes  26  during use of the tool holder  10 .  
     [0073] The embodiment shown in FIG. 14 is described while mentioning the case where the adjustment members  27  of the same length and the same mass are screwed into all of the threaded holes  26 , respectively. However, the present invention is not limited thereto. For example, an adjustment member(s) similar to that shown in FIG. 3 may be screwed into an appropriate threaded hole(s) as in the case of FIG. 3.  
     [0074] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.