Abstract:
A rotatable chuck for clamping a shank portion of a rotatably operating machining tool includes a rotatable chuck body provided with a cylindrical bore concentric with a rotation axis of the chuck body. The circumferential surfaces of a clamping portion of the bore are arranged to apply a clamping force around the circumference of the shank portion of the tool when it is mounted in the chuck to fixate the tool in the chuck. The chuck is provided with auxiliary pull out preventing means for preventing inadvertent pull out of the tool in the axial direction of the bore during machining operation, as well as auxiliary rotary preventing means for preventing inadvertent rotation in at least one direction in relation to the chuck during machining operation. The auxiliary pull out and rotary preventing means include an attachment member positionable in an inner portion of the bore and attachable to the shank portion to be clamped, such that the tool and the attachment member will be prevented from being pulled apart in the axial direction and from being rotated in at least one direction in relation to each other.

Description:
TECHNICAL FIELD 
     The present disclosure relates to a rotatable chuck for clamping a shank portion of a rotatably operating machining tool. 
     BACKGROUND 
     Chucks for clamping a shank portion of a rotatable machining tool, such as a milling cutter or a drill, are well known within the machining industry, especially for machining work pieces of steel or other metals, but also for wood and plastics. Such a chuck is in its turn mounted in a suitably designed machine for rotatably driving of the chuck. Usually, the attachment of the tool is accomplished purely by frictional clamping, such that clamping surfaces within a clamping bore of the chuck are tightened around the shank portion. The clamping force can be generated in different ways, such as mechanical displacement of clamping jaws inside the clamping bore, hydraulic deflection of a clamping insert or collet inside the clamping bore or thermal crimping of the chuck body around the shank portion. 
     One problem with a purely frictional clamping of the shank portion of the machining tool is that, despite applying a maximal possible clamping force, the machining tool may during operation tend to rotate and/or be displaced in the axial direction in relation to the chuck. The reason for this is usually to be found in the combination of the vibrations to which the machining tool is exposed during the machining operation, especially when the machining is performed at high rotational speed, and the tangential and axial forces acting on the tool during operation. 
     The above problem can be overcome by a frictional clamping chuck and a milling cutter as disclosed in U.S. Pat. No. 8,505,893, in which the inner end portion of the milling cutter is provided with helical or L-shaped locking grooves, which are adapted to engage with balls or pin-shaped locking elements. In an alternative embodiment in that document, the circumferential surface at the inner end portion of the shank of the machining tool is provided with a male thread, which is in engagement with a female thread in the inner portion of the bore. With a chuck formed in this way, the machining tool will, due to the locking grooves or threads, be prevented from rotation, in at least one direction, as well as be prevented from being pulled out in the axial direction from the bore. 
     However, there are also several drawbacks with a chuck and machining tool designed as in U.S. Pat. No. 8,505,893. Since the envelope surface of the tool shank is provided with some kind of threads or locking grooves, the clamping zone between the chuck and the tool will be negatively affected in one way or the other. For example the clamping portion of a hydraulic expansion chuck is not well suited to clamping around threads or grooves, since this could cause permanent deformation of the hydraulically deflectable sleeve inside the chuck. Also, the ball- or pin-shaped locking elements cannot be allowed to penetrate through the channels and spaces for hydraulic fluid between the deflectable collet and the chuck body, nor can a female thread be formed in the deflectable collet. Accordingly, in this case the clamping portion of the chuck has to be made shorter, which will render the frictional clamping forces acting on the tool lower, or alternatively to make the tool shank and the chuck bore longer, which will increase the quantity of material for manufacturing the tool, and hence increase the costs, and take up more space inside the chuck, which accordingly also has to be made longer. 
     For a mechanically operated draw-in collet chuck, the ball- or pin-shaped locking elements will complicate the design and disturb the function of the clamping jaws and a female thread cannot be formed in the clamping jaws. Accordingly, the clamping zone between the clamping jaws and the tool shank will be reduced due to the threads or locking grooves with lowered frictional clamping force as a result, unless this is compensated by an extended tool shank and chuck bore. Also, in case of a thermal expansion chuck the thread or the locking grooves may reduce the frictional clamping force, which may have to be compensated by an extended tool shank and chuck bore. Moreover, should the machining tool break such that only the tool shank is left inside the chuck bore, the remaining tool shank is very difficult to remove from the chuck bore. 
     In addition to the above mentioned drawbacks, the embodiment having a male thread on the envelope surface of the tool shank and a female thread inside the chuck bore will be difficult and hence costly to produce, since the female thread has to be shaped in the bottom of a rather narrow bore. 
     SUMMARY 
     An aspect of the present disclosure is to provide a rotatable chuck, which in addition to being able to fasten a rotatable operating machining tool by applying a frictional clamping force around a shank portion of the tool, can in a simple and reliable way, lock the tool in the chuck against rotation in at least one direction, as well as against pull out from the chuck in its axial direction, and also to release the tool from the chuck. At least this aspect is achieved by a chuck having a rotatable chuck body provided with a cylindrical bore being concentric with a rotation axis of the rotatable chuck body, wherein circumferential surfaces of a clamping portion of the bore are arranged to apply a clamping force around the circumference of the shank portion of the tool when it is mounted in the chuck to fixate the tool in a well-defined position in the chuck, and wherein the chuck also is provided with auxiliary pull out preventing means, for preventing inadvertent pull out of the tool in the axial direction of the bore during machining operation, as well as auxiliary rotary preventing means for preventing inadvertent rotation in at least one direction in relation to the chuck during machining operation. 
     Accordingly, this aspect may be achieved by a chuck including an attachment member positionable in an inner portion of the bore and attachable to the shank portion to be clamped such that the tool and the attachment member will be prevented from being pulled apart in the axial direction, as well as be prevented from being rotated in at least one direction in relation to each other. The rotatable chuck body also has an axial pull out preventing means, as well as a rotary preventing means in at least one direction arranged to engage with the attachment member. There are several advantages with arranging the pull out and rotary preventing of the machining tool by an auxiliary attachment member. For example, in case it is desirable to change the rotary direction of the tool, only the tool and the attachment member need to be exchanged without the need for exchanging the entire chuck body. Also, in case the machining tool should break, such that only the tool shank is left inside the chuck bore, it is easy to release the remaining tool shank by releasing the attachment member from the chuck body. 
     Within this overall aspect, a chuck according may be formed in many different ways. For example, in the hereinafter described and illustrated embodiments, the engagement coupling between the tool shank and the attachment member is formed as a conical thread or a bayonet coupling, by which the male parts of the conical thread and the bayonet coupling are formed in the end of the shank portion, whereas the female parts are formed in the attachment member. However, it is to be understood that many other types of engagement couplings could be conceivable. For example, to form the threads as ordinary straight threads on a shank portion having a uniform cross-section or to form the male parts of the threads or the bayonet coupling in the attachment member and the female parts in the shank portion. 
     Also, the bayonet coupling could be formed in many different ways, e.g. as projecting pins in one of the attachment member or the shank portion which are adapted to go into engagement within grooves formed in the other. One advantage with an engagement coupling in form of a conical thread or a bayonet coupling is that the tool and the attachment member can be attached with or released from each other by means of just a short rotation of the tool, normally in order of just a quarter to a half of a full turn, which makes the attachment easy and quick. A straight thread, on the other hand, requires a larger rotation, at least one full turn and normally several full turns. 
     Both the conical thread and the bayonet coupling, as disclosed herein, provide a connection which prevents pull out of the tool shank in the axial direction from the attachment member, as well as rotation of the tool shank in one direction in relation to the attachment member. However, a bayonet coupling could also be designed to prevent the tool shank from being rotated in both directions, e.g. by a spring biasing of the bayonet coupling such that the attachment member and the shank portion are pushed in a direction away from each other and a projecting portion of the bayonet coupling at either the attachment member or the shank is pushed into a recess in the other. 
     Also, the attachment member and the chuck body are each provided with axial pull out preventing means, as well as rotary preventing means, which are arranged to interact to enable connecting the attachment member and the chuck body together in an axial pull out preventing and rotary preventing way. 
     In a hereinafter described and illustrated first embodiment, the rotary preventing means are in form of splines in the axial direction on the outside of the attachment member and mating internal splines inside a mounting portion inward of the chuck bore which are arranged to interact with each other in order to secure the attachment member against rotation in both directions. 
     It is to be understood however, that the rotary preventing means for the attachment member could be made in many different ways, for example, as a single ridge in a single groove or as twisted splines having an angle in relation to the axial direction. The pull out preventing means are in form of a screw having external threads, which are arranged to rotatably engage with mating internal threads inside the chuck body, as well inside a hole in the attachment member in order to secure them together in the axial direction. 
     In a second embodiment, the attachment member is formed with a yoke, having two yoke shanks at its inner end portion. The yoke shanks are, along their inner surfaces, provided with diagonally oppositely directed grooves. Two locking rods, which are adjustably telescoping interconnected and accommodated in a hole transverse to the axial direction of the chuck, are extended through the space between the yoke shanks. The locking rods are provided with guide surfaces having diagonally oppositely directed ridges, which mate with and are in engagement with the diagonally oppositely directed grooves in the yoke shanks of the attachment member. Accordingly, the locking rods and the attachment member interact by means of the diagonally oppositely directed grooves and ridges, as well as by the yoke shanks to prevent pull out of the attachment member in the axial direction and rotation in both directions. The more precise function of the interaction between the attachment member and the locking rods will be described in relation to the detailed description of the exemplary embodiment. 
     In a further aspect, the projecting of the tool from a chuck having an attachment member can be readily adjusted. According to this aspect, there is provided a chuck in which the position of the attachment member is continuously adjustably displaceable and lockable in different positions within the chuck body. A great advantage with a chuck designed in this way is that the machining depth of the machining tool can be carefully regulated for high quality precision machining. 
     Although both of the hereinafter described and illustrated embodiments relate to hydraulically operated clamping chucks, it is to be understood that the invention is applicable on all types of clamping chucks, such as mechanically and thermally operated clamping chucks. 
     The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a chuck according to a first embodiment which carries a shank end mill. 
         FIG. 2  is a perspective longitudinal cross-section of the chuck according to  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the chuck in  FIG. 2 . 
         FIGS. 4 a -4 b    are longitudinal cross-sections of the chuck according to  FIGS. 1-3  showing the shank end mill in two different projecting positions. 
         FIG. 5  is a partly exploded and longitudinal cross-section through a portion of the chuck, illustrating the regulating mechanism for regulating the projection of the shank end mill from the chuck. 
         FIG. 6  is a perspective view of a chuck according to a second embodiment which carries a shank end mill. 
         FIG. 7  is a perspective longitudinal cross-section of the chuck according to  FIG. 6 . 
         FIG. 8  is an exploded perspective view of the chuck in  FIG. 7 . 
         FIGS. 9 a -9 b    are longitudinal cross-sections through the chuck of  FIGS. 6-8  showing the shank end mill in two different projecting positions. 
         FIG. 10  is a view of the shank end mill and the attachment member in an assembled state. 
         FIG. 11  is a cross-section taken along line XI-XI of  FIG. 10  illustrating the bayonet coupling between the shank end mill and the attachment member. 
         FIG. 12  is a longitudinal cross-section through the chuck body and attachment member illustrating the bayonet coupling between the shank end mill and the attachment member, as well as the combined pull out preventing means and the projection regulating mechanism for the shank end mill. 
         FIG. 13  is a cross-section taken along line XIII-XIII in  FIG. 12  illustrating the projection regulating mechanism for the shank end mill. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     It is to be noted that the terms inner, inward and the like as used herein throughout the specification and claims, refers to a direction as seen from the mouth of the chuck bore along the rotary axis of the chuck body. The terms outer, outward and the like, refers accordingly to the opposite direction. 
     Referring to  FIGS. 1-5 , a first embodiment of a chuck will be described. The chuck includes a general rotationally symmetric chuck body  1  of a generally homogenous metal material, which is rotatable around a rotation axis  2 . The chuck body has one end formed with an attachment portion  3 , which in the embodiments shown herein is in form of a tapered, non-circular shaft of a commonly known type arranged to be secured to a mating motor-driven spindle (not shown) of a working machine. At the opposite end the chuck body is provided with a circular cylindrical chuck bore  4 , which is arranged to receive and clamp a shank  5  of a machining tool  6 . A shank of a machining tool in form of a shank end mill is shown inserted into the chuck bore of the various drawings. 
     The chuck is of the kind which clamps the tool shank by hydraulic pressure. For this purpose, the chuck is provided with a hydraulic clamping element in the form of a rather thin-walled clamping collet  7  inserted into the chuck bore, as is best seen in  FIGS. 4 a - b   . In a way known per se, the collet is at least at its ends connected to the chuck body  1  in a fluid- and gas-tight fashion, e.g. by soldering. The intermediate portion of the collet between its ends is disengaged from the chuck body and fluid channels  8  for the hydraulic fluid are arranged in the area between the collet  7  and the chuck body  1  into which pressurized hydraulic fluid may be fed through a hydraulic supply channel  9  from a pressure generating means (not shown), which for example can be formed as a hydraulic piston controllable by means of a screw or the like, which are positioned inside of a hole  10  in the chuck body  1 , as is shown e.g. in  FIGS. 1 and 6 . When pressurized hydraulic fluid is forced into the space between the collet  7  and the chuck body  1 , the collet will tend to deflect inwards and accordingly clamp around the tool shank  5 . 
     According to the present disclosure, the chuck is provided with an attachment member, which is positionable in a mounting portion  11  located at an inner end of the chuck bore  4 . In a first embodiment, illustrated in  FIGS. 1-5 , the attachment member is formed as a sleeve  12  having a generally circular cross-section. The envelope surface of the sleeve is formed with splines  13  having grooves and ridges in the axial direction. The mounting portion  11  has a generally circular cross-section and is formed with splines  14  having grooves and ridges in the axial direction around its circumference, which mate with the splines  13  of the sleeve  12  such that the sleeve can be inserted with a snug fit within the mounting portion  11 . Accordingly, when the sleeve  12  is positioned within the mounting portion it will be prevented from rotating, but will be displaceable in the axial direction. Preferably, the grooves of the splines on the circumference of the mounting portion may have a part-circular shape in cross-section. With grooves shaped in this way, they can easily be machined by means of a shank end mill, which is beneficial because of the limited space at the end of the chuck bore. Accordingly, it is also preferred that also the ridges of the splines at the attachment member have a part-circular shape in cross-section. 
     In the first embodiment, the machining tool  6  in form of a shank end mill, is attachable to the sleeve shaped attachment member  12  by means of a conical shaped male thread  15  formed in the end of the tool shank  5 , which can be threaded into a mating conical female thread in the outer end of the sleeve. This is best illustrated in  FIGS. 3 and 5 . When the tool  6  is threaded into engagement with the attachment member  12 , the tool will be prevented from being pulled apart in the axial direction from the attachment member and will also be prevented from being rotated in one direction in relation to the attachment member. 
     The attachment member  12  is in turn attachable to the chuck body  1  by means of a double-threaded regulating screw  16 , as shown in  FIG. 3 , having a right-hand thread  17  in one end portion, which end is also formed with a suitable engagement formation, e.g. in form of an Allen aperture  18 , for engagement and rotation by means of a tool, e.g. an Allen key  19 . The other end portion of the regulating screw is formed with a left-hand thread  20 . The right-hand thread  17  can be threaded into a matching right-hand female thread in a hole  21  inside the chuck body at the inner end of the mounting portion for the attachment member, whereas the left-hand thread  20  can be threaded into a mating left-hand female thread in a hole  43  at the inner end of the attachment member  12 . 
     With a chuck as described above, the tool  6  can be securely mounted in the chuck bore, on the one hand, by means of a clamping force from the hydraulic pressure acting on the tool shank  5  from the deflectable collet  7 , and, on the other hand, can be prevented from being pulled out in the axial direction, as well as being rotated in one direction by means of the threaded connection between the tool shank  5  and the attachment member  12 , which in its turn is prevented from being rotated in relation to the chuck body  1  by means of the splines connection  13 ,  14  between the attachment member  12  and the mounting portion  11  of the chuck body, as well as being prevented from being pulled out from the chuck body by means of the double-threaded regulating screw  16  interconnecting the attachment member  12  and the chuck body  1 . 
     Furthermore, by means of the chuck, the projecting length of the tool  6  from the chuck body  1  can readily be regulated, such as is schematically illustrated in  FIGS. 4 a  and 4 b   . More precisely, before clamping the tool shank  5  by applying a hydraulic pressure on the clamping collet  7 , the projecting length can be regulated by rotating the regulating screw  16  by means of a tool, e.g. an Allen key  19 , from the inner end of the chuck body. By rotating the Allen key in the direction as illustrated in  FIG. 4 a   , the attachment member  12  can, due to the splines connection  13 ,  14 , be drawn further into the mounting portion  11  of the chuck body, which will also draw the machining tool  6  further into the chuck bore  4 . When, on the other hand, the Allen key  19  is rotated in the opposite direction, as illustrated in  FIG. 4 b   , the attachment member  12  will be displaced outwards from the mounting portion  11  and the machining tool  6  will also be displaced outwards in relation to the chuck bore. When the correct projecting length of the machining tool has been obtained, a hydraulic pressure is applied to the clamping collet  7 , which accordingly will clamp around the tool shank  5 . 
     A second embodiment of the chuck, as illustrated in the  FIGS. 6-13 , has a similar outer appearance as the first embodiment which can be seen from  FIG. 6 . Accordingly, the chuck includes a general rotationally symmetric chuck body  1  of a generally homogenous metal material which is rotatable around a rotation axis  2 . The chuck body is at one end formed with an attachment portion  3 , which in the embodiments shown herein is in form of a tapered, non-circular shaft of a commonly known type, which is adapted to be secured to a mating motor-driven spindle of a working machine (not shown). In the opposite end the chuck body is provided with a circular cylindrical chuck bore  4 , which is arranged to receive and clamp a shank  5  of a machining tool  6 . A shank of a machining tool in form of a shank end mill is shown inserted into the chuck bore of the various drawings. Also, this chuck is of the kind, which clamps the tool shank by means of hydraulic pressure. For this purpose, the chuck is provided with a hydraulic clamping element in form of a rather thin-walled clamping collet  7  inserted into the chuck bore, as is best seen in  FIGS. 9 a  and 9 b   . The clamping collet is identical with and functions in the same way as the clamping collet described in relation to the first embodiment. 
     However, the chuck according to this embodiment differs from the first embodiment in that the attachment member, the regulating mechanism of the attachment member and the connection between the tool shank and the attachment member are differently designed. Here, the attachment member has the overall shape of a yoke  22  having two yoke shanks  23 ,  23  projecting inward in the axial direction from a cylindrical base part  24  having a circular cross section and which in an outer end is provided with a female bayonet coupling part  25  mating with a male bayonet coupling part  26  in an inner end of the tool shank  5 . 
     The bayonet coupling  25 ,  26  is illustrated in more detail in  FIG. 11 , which is a cross section along the line XI-XI in  FIG. 10  which shows the attachment member  22  and the machining tool  6  in an assembled state. As evident from  FIG. 11  in combination with  FIGS. 9 a  and 9 b   , the male bayonet coupling part  26  of the tool is formed with a shank portion  27  having a circular cross-section closest to the tool shank, and an inner head portion  28  having a somewhat triangular shape. The female bayonet coupling part  25  has a somewhat triangular inlet opening closest to the outer end of the attachment member  22 , through which the triangular head  28  of the male bayonet coupling part  26  may pass. 
     Inward from the triangular inlet opening, the female bayonet coupling part  25  is formed with recesses  30  in the areas between the apexes  31  of the triangular inlet opening, such that when the triangular head  28  of the male bayonet coupling part  26  has passed the triangular inlet opening of the female bayonet coupling part, the male and female bayonet coupling parts can engage with each other by a further minor rotation of the tool shank  5  in relation to the attachment member  22  to the position as illustrated in  FIG. 11 . In this position the apexes  32  of the triangular head  28  of the male bayonet coupling part  26  will be locked in the recesses  30  against pull-out in the axial direction, as well as against rotation in one direction. As is evident from  FIG. 12 , the chuck is also provided with a spring  33  in the inner end of the female bayonet coupling part  25  acting to press the male bayonet coupling part  26  and accordingly also the machining tool  6  in an axial direction outward. 
     With reference to the  FIGS. 7, 8, 9   a ,  9   b ,  12  and  13 , hereinafter follows a description of the pull out and rotary preventing means for the attachment member  22 , as well as of the mechanism for regulating the axial projecting length of the machining tool  6  from the chuck. As is evident from the drawings, two locking rods  34 ,  34  are accommodated in a hole  35  transverse to the axial direction of the chuck and are extended through the space between the yoke shanks  23 ,  23  and partly overlap each other. The locking rods are adjustably telescoping interconnected by means of a regulating rod  36  having one right-hand thread  37  and one left-hand thread  38 . The regulating rod is extended through and in threaded engagement with a hole  39  in each of the locking rods, such that when rotating the regulating rod  36  in one direction by means of a suitable tool, such as by e.g. an Allen key  19  in engagement with an Allen aperture  40  in one of the ends of the regulating rod, the locking rods  34 ,  34  will be displaced in a direction apart from each other, and when rotating the regulating rod in the other direction, the locking rods will be displaced in a direction towards each other. Moreover, the yoke shanks  23 ,  23  are in the inner surfaces facing each other, provided with diagonally oppositely directed grooves  41 , and the locking rods are provided with guide surfaces which, in the assembled state of the mechanism, are facing in opposite directions and are provided with diagonally oppositely directed ridges  42 . 
     In the assembled state of the mechanism, the diagonally oppositely directed grooves  41  of the yoke shanks and the diagonally oppositely directed ridges  42  of the locking rods are in engagement with each other such that pull out of the attachment member in the axial direction, and hence also the machining tool, is prevented. Since the attachment member  22  is formed as a yoke and the locking rods extends through intermediate space between the two yoke shanks, the attachment member will also be prevented from rotation in both directions. 
       FIGS. 9 a  and 9 b    illustrate the procedure for regulating the projecting length of the machining tool  6  from the chuck. When rotating the regulating rod  36  in one direction by means of an Allen key  19 , as is illustrated in  FIG. 9 a   , the locking rods  34 ,  34  will be synchronously displaced in a direction towards each other. Accordingly, the engagement between the diagonally oppositely directed ridges  42  of the locking rods and the diagonally oppositely directed grooves  41  of the yoke shanks  23 ,  23  will cause a retraction of the attachment member  22 , and hence also the machining tool  6  into the chuck. When, on the other hand, the regulating rod  36  is rotated in the opposite direction, as is illustrated in  FIG. 9 b   , the attachment member and the machining tool will be synchronously displaced in a direction outward from the chuck. The synchronous displacement of the locking rods is advantageous since the dynamic balance of the chuck will be maintained regardless of the projecting length of the machining tool. It is also advantageous to be able to regulate the projecting length of the machining tool from a direction transverse to the rotary axis of the chuck, since it is possible to regulate the projecting length while the chuck is mounted in the machine. With a chuck according to the first embodiment it is necessary to first remove the chuck from the machine before performing the regulating. 
     Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.