Precision chuck

Abstract: In a chuck a plunger (64) slidably fitted into a body (40) is provided with wedge-shaped projections (65) and a plurality of jaws (46) which are coupled to the projections in such a manner that they are displaced in a radial direction with respect to the body in response to displacement of the plunger. The engaging portion of each jaw (46) with the respective wedge projection (65) is defined at the radial centre of the jaw (46). The body (40) is a unitary structure and is formed with a guide surface (42) which is in sliding contact with the plunger (64) over the whole range of displace­ ment of the plunger, and a bearing surface for supporting the inner and/or outer peripheral surface of the wedge is defined in the guide surface (42).

Description: The present invention relates to a precision chuck comprising a body of unitary construction; a plunger being movable forward and rearward in the axial direction of the body; a plurality of jaws being movable inward and outward in the radial direction of the body in response to a relative axial movement of the plunger, in which body wedges are operatively connected to be plunger for a movement in axial direction, each wedge providing guide surfaces parallel to the axial direction and guide surfaces inclined to the axial direction; whereby jaw bodies are operatively connected to the wedge for movement in radial direction of the jaws, the jaw bodies having forward radial guide surfaces and rearward radial guide surfaces, and inner and outer axially inclined guide surfaces engaging the inclined guide surfaces of the wedges; first guide means are formed in axial direction on the body in order to guide and move the body wedges forward and rearward in axial direction, each first guide means having both outer axial guide surfaces and inner axial guide surfaces; and second guide means are formed in radial direction on the body in order to guide and move the jaw bodies inward and outward in radial direction, each second guide means having both forward radial guide surfaces and rearward radial guide surfaces and that the engaging portions between the inclined guide surfaces of the body wedge and the corresponding inclined surfaces of the jaw are always located within the range of the axial length of the parallel guide surfaces of the body wedge in any operational position, and the first guide means are formed on the body over the full range of the axial movement of the body wedge, whereby the parallel guide surfaces of the body wedge are always supported in its full length by the first guide means of the body. A chuck of the type described above is, for example, disclosed in Japanese Patent Publication No. 57-46965 and is shown in Figs. 1 and 2. In this chuck, an axially movable annular plunger 3 is fitted into a central bore 2 formed through a body 1 and is formed with a plurality of equiangularly spaced apart T-shaped wedge grooves 4. The body 1 is formed with a plurality of radially extended guide grooves 5 into which are radially slidably fitted master jaw 6 connected top jaw adapted to chuck a workpiece. The rear inner end portion remote from the corresponding top jaw of the master jaw 6 is formed with a T-shaped wedge portion 7 adapted to fit into the corresponding T-shaped wedge groove 4 of the plunger 3. The front surface of the master jaw 6 is formed with front guided surfaces 8 while the rear surface thereof is formed with rear guided surfaces 9 and these front and rear guided surfaces 8 and 9 are in opposed relationship with side surfaces 10 of the guide groove 5 of the body 1. A cover 11 for preventing the intrusion of chips and dust particles is fitted into the plunger 3. The chuck with the above-described construction has a defect that the length L of the contact between the side surface 10 of the guide groove 5 of the body 1 and the front guided surface 8 of the master jars 6 is greater than the length 1 of the contact between the side surface 10 of the guide groove 5 of the body 1 and the rear guided surface 9 of the master jaw 6; that is, L > 1. Because of this difference in the length of contact, there exists a great difference in the displacement or floating of the master jaw 6 under an external force between the time when the external peripheral surface of a workpiece is held and the time when the internal peripheral surface of a workpiece is held so that it results a difference in workpiece holding accuracy between the case in which the inner peripheral surface of a workpiece is held and the case in which the outer peripheral surface of a workpiece is held. In addition, the friction between the rear guided surface 9 of the master jaw 6 with the body is greater than the friction between the front guided surface 8 of the master jaw 6 with the body, the rear guided surface 9 is quickly worn out. As a result, the workpiece-holding-accuracy in case of holding the inner peripheral surface of a workpiece becomes lower that in case of holding the outer peripheral surface of a workpiece and moreover there arises the problem that the sliding resistance encountered by the master jaw 6 in case of holding the inner peripheral surface of a workpiece becomes higher than that in case of holding the outer peripheral surface of a workpiece. In order to eliminate the above and other defects encountered in the prior art chucks, Japanese Patent Application Laid-Open No. 60-94207 discloses a chuck as shown in Figs. 3 and 4. The chuck has a two-split body 20 consisting of an axially front body section 21A and an axially rear body section 21B and a center hole 22 is bored through the front and rear body sections 21A and 21B. The front body section 21A is provided with a plurality of radially extended guide grooves or recesses 23 and a master jaw 24 is slidably fitted into respective guide grooves or recesses 23 for slidable movement in the radial direction of the front body section 21A. An annular cylinder 25 is interposed between the front and rear body sections 21A and 21B and an annular piston 26 is fitted into the cylinder 25 for slidable movement in the axial direction. One end of the piston 26 is made into threadable engagement with a base portion 28 of a plurality of wedges 27 which are in opposed relationship with the master jaw 24. Each wedge 27 is provided with a pair of wedge main bodies 29 which are extended from the base portion 28 and which are spaced apart from each other by a predetermined distance. Each wedge main body 29 is so tapered that its height (or thickness) is gradually increased toward its front end. Meanwhile each master jaw 24 is formed with tapered guide surfaces 30 on both sides of the radial centerline thereof for engagement with the wedge main bodies 29 extended from the base portion 28. With the above-described construction, the wedge main bodies 29 of the wedge 27 are made into engagement with each other at the radial centerline of the master jaw 24 so that the workpiece-holding-accuracy can be well balanced as compared with the prior art chuck in which the wedge main bodies 29 are made into engagement with each other at the radially inward portion and at the rear portion in the axial direction of the master jaw 6. However, the body 20 consists of the front and rear body sections 21A and 21B splitted in the axial direction so that the guide surface 32 of the front body section 21A which supports the wedge main body 29 of the wedge 27 and the inner peripheral surface of the cylinder 25 of the rear body section 21B which supports the piston 26 threaded into the base portion 28 of the wedge 27 must be machined by completely different machining means and steps. As a result, there arises the problem that it becomes impossible to maintain the guide surface 32 in completely coplanar relationship with the inner peripheral surface of the cylinder 25 in the axial direction. Because of the above-described problem, only the inner peripheral surface of the cylinder 25 which guides the outer peripheral surface of the sliding piston 26 becomes a reference surface for guiding the wedge 27. As a result, the guide surface 32 cannot support the wedge 27 in a stable manner so that there is a defect that the base portion of the wedge main body 29 of the wedge 27 is cracked. More particularly, when the driving force exerted to the piston 26 is transmitted through the wedge 27 to the master jaw 24, the relative slidable movement between the inner peripheral surface of the cylinder 25 and the outer peripheral surface of the piston 26 with a minimum gap therebetween is maintained, thereby maintaining a desired degree of workpiece- holding-accuracy. Furthermore, the wedge main bodies 29 are merely fitted into axial holes 31 of the front body section 21A and the wedge main bodies 29 of the wedge 27 are made into engagement with the guide surfaces 32 of the front body section 21A only under the following conditions. In order to maintain a satisfactory degree of workpiece-holding-accuracy in the conventional machining processes, the wedge main bodies 29 are so designed and constructed to have a sufficient degree of rigidy so that they may be used as a cantilever. That is, when the machining force which is externally exerted to a workpiece increases beyond a predetermined point so that excessive loads are exerted to the wedge main bodies 29, the guide surfaces 32 then support the wedge main bodies 29 to bear part of the excessive loads exerted thereto so that the base portion of the wedge main bodies 29 is prevented from being cracked. In this case, the base portion of the wedge main bodies 29 is considerably deformed so that the workpiece-holding-accuracy is naturally degraded. Therefore, the chuck disclosed in Japanese Patent Application Laid-Open No. 60-94207 and described above with reference to Figs. 3 and 4 cannot attain a sufficient holding force and is not adapted to be rotated at high rotational velocities. As a result, it cannot be used in the recently-developed high-rotational-velocity machine tools. Furthermore, the other example of the prior art chuck is disclosed in US-A-3,814,451. The chuck has a one-piece body and the body is provided with bearing surfaces for supporting the inner and outer peripheral surfaces of a wedge. With the above-described construction, the body can support the wedge in a relative stable manner. However, the forward free end of the wedge faces the wide portion of the jaw, so that at the more forward side of the engaging portion of the wedge with a corresponding one of the jaws there is no supporting surface of the body to support a the wedge. In these circumstances, the wedge is supported by the body in a cantilever like manner at one axial side only with the result that the support for the wedge may not be sufficiently stable. Unlike the underlying principle of the prior art chucks to prevent breakdowns of the component parts due to considerable deformations thereof, the underlying principle of the present invention is to design and construct a precision chuck whose deformation can be reduced to minimum, whereby the workpiece-holding-accuracy can be enhanced. Therefore, one of the objects of the present invention is to provide a precision chuck which can substantially overcome the above and other problems encountered in the prior art chucks based upon the above-described underlying principle of the present invention, which can permit the quick displacement of jaws, which can attain a great holding force and a high degree of workpiece-holding-accuracy and which is adapted to be rotated at high rotational velocities. Furthermore, another object of the present invention is provide a precision chuck in which, in order to attain a high degree of workpiece-holding-accuracy unattainable by any prior art chucks, a plunger is securely supported by a body which has a high degree of mechanical strength and which can be machined with a high degree of dimensional accuracy without resorting to different machining means and steps. According to the invention of the precision chuck is characterized in that the axial length of the inclined guide surfaces of the body wedge is so much larger than the axial length of the corresponding inclined guide surfaces of the jaw that the guide surfaces of the jaw engage the guide surfaces of the body wedge over its full length in any operational position. Guiding opposite ends of the wedges in the chuck body on opposite sides of the grooves supports the wedges on both sides of the grooves which provides a construction in which deformation or deflection of the wedges can be reduced at a minimum, and a maximum stability is achieved- Specifically the chuck body supports the wedge body at at least both ends thereof but does not support the wedge portion. Thus each wedge body acts as a simply supported beam. According to the present invention, the engaging portion of each jaw is defined at the centre in the radial direction of the jaw so that the frictions resulting from the sliding contacts between the body and the radial inner and outer portions of the jaw become substantially equal and can be decreased, whereby the quick displacement of the jaws can be ensured. Furthermore, the body is a unitary structure so that it becomes robust. Moreover, the body in the form of a unitary structure as described above is formed with guide surfaces over the whole range of movement of the plunger so that a bearing surface for supporting the inner and/or outer peripheral surface of the wedge can be defined, whereby the plunger can be supported in a stable manner with a high degree of accuracy. In addition, the engagement in the radial direction of the body between the guide groove of the body and the jaw is so maintained that the whole jaw is always located within the guide groove of the body, the displacement of the jaw can be reduced to a minimum in case of holding a workpiece and the workpiece-holding-accuracy can be further enhanced. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a longitudinal sectional view of a prior art chuck illustrating the major component parts thereof; Fig. 2 is a perspective view of a master jaw thereof; Fig. 3 is a right side view of another prior art chuck; Fig. 4 is a longitudinal sectional view thereof; Fig. 5 is a longitudinal sectional view of a first embodiment of the embodiment of the present invention illustrating the major component parts thereof; Fig. 6 is a sectional view of a guide groove of the body shown in Fig. 5; Fig. 7 is a perspective view of a wedge of the first embodiment shown in Fig. 5: Fig. 8 is a perspective view illustrating the engagement between the wedge and the master jaw; Fig. 9 is a perspective view of a piston of the first embodiment shown in Fig. 5; Fig. 10 is a longitudinal sectional view of the first embodiment shown in Fig. 5 used to explain the forces acting on the wedges; Fig. 11 and 12 are longitudinal views illustrating modifications of wedges, respectively; Fig. 13 is a longitudinal sectional view of a second embodiment of the present invention illustrating the major component parts thereof; Fig. 14 is a perspective view of a piston thereof; Fig. 15 is a sectional view taken along the line XXVIII-XXVIII of Fig. 13; and Fig. 16 is a sectional view illustrating an optimum embodiment of a fork-end-shaped wedge. Fig. 17 is a perspective view of a master jaw of a first embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION: First embodiment, figs. 5 to 10. A first embodiment of a precision chuck in accordance with the present invention as shown in Figs. 5 - 10 uses a master jaw shown in Fig. 17 of the type where the jaw body 122 is formed with wedge grooves 123 in both the side surfaces thereof which are inclined downwardly toward a top jaw. Each wedge groove 123 is defined by a flat upper surface 124, a flat guide surface 125 and a flat lower surface 126. The guide or sliding surfaces 125 of the wedge grooves 123 are gradually converged toward the front portion of the master jaw 120. In other words, the thickness between the guide or sliding surfaces 125 are gradually decreased toward the front portion of the master jaw 120. Recesses 129 are formed in both the side surfaces of a joint 127 which is connected to a top jaw (not shown). The recesses 129 define sliding surfaces 128 which are in coplanar relationship with the sliding surfaces 125 and in contiguous therewith. Referring first to Fig. 5 illustrating the major component parts of the first embodiment, a body 140 is formed with an inner sliding surface 141 which is coaxial with the axis of the body 140 and a plurality of equiangularly spaced apart sliding holes 142 are drilled radially outwardly of the inner sliding surface 141. The front end surface of the body 140 is formed with a plurality of guide grooves 143 each having a T-shaped cross sectional configuration as best shown in Fig. 6 in such a manner that the front side of each guide groove 143 is opened. As best shown in Fig. 7, a wedge 144 inserted into each sliding hole 142 is in the form of a fork end in which a pair of wedge main bodies 146 which are perpendicular the lengthwise direction of a base portion 145 are extended in parallel with each other from both the ends of the base portion 145 and wedge portions 147 rectangular in cross section are defined on the opposing inner surfaces of the wedge main bodies 146 in such a way that they are inclined downwardly from the base to the leading end thereof and that the spacing between the wedge portions 147 is gradually decreased from the leading ends toward the bases thereof. Each of the wedge main bodies 146 has a rectangular cross sectional configuration and its upper and lower surfaces are supported by the sliding hole 142. An engaging projection 148 is extended from the lower surface of the wedge 144 in the lengthwise direction thereof and the lower surface 149 of the engaging projection 148 is inwardly arcuated in such a manner that the midpoint between the ends of the arcuate surface 149 is higher than the ends of the arcuate surface 149. The engaging projection 148 has a function of transmitting the sliding displacement force from a draw bar (not shown) through a piston 150 to the wedge 144. The master jaw 120 is inserted into a guide groove 143 of a body 140 as shown in Figs. 5 and 6 and is adapted to open or close by the slidable displacement in the radial direction of the body 140. The detailed construction of the master jaw 120 has been already described with reference to Fig. 17 and, as best shown in Fig. 8, each wedge 147 of the wedge main body 146 is inserted into the corresponding wedge groove 123 of the master jaw 120. The master jaw 120 has a T-shaped cross sectional configuration and serves as a guided inner surface when the front guided surfaces 151 and the rear guided surface 152 of the jaw body 122 are fitted into the guide groove 143 of the body 140 and are displaced in the radial direction of the body 140. Both the side surfaces 176 of the narrow joint 127 are used as guided surfaces and the front end portion of the joint 127 is extended outwardly of the body 140, whereby a front serrated surface 154 engages securely with a top jaw 155. The narrow joint 127 of the master jaw 120 as shown in Fig. 6 is defined with one portion of which both side surfaces are parallel and another portion of which both side surfaces are reduced in width as they extend toward the front portion. The narrow joint 127 is supported by the guide surfaces 177 of the front open portion of the body 140 with the parallel surfaces only acting as guided surfaces. The master jaw 120 is made into engagement with the wedge 144 as shown in Fig. 5. As best shown in Fig. 9, the piston 150 has a cylindrical sliding portion 157 which can be slidably fitted into the enlarged-diameter center bore 141 of the body 140 and an annular projection 159 adapted to be fitted into the reduced-diameter center bore 158 of the body 140 is extended from the leading end of the sliding portion 157. A boss 160 is extended backwardly of the sliding portion 157 and has an internally threaded screw 161 for threadable engagement with a draw bar (not shown). A circumferential engaging groove 163 into which is relatively intimately fitted the engaging projection 148 of the wedge 144 is formed in the outer peripheral surface 162 of the sliding portion 157 at the midpoint between the axial ends thereof. Furthermore the outer peripheral surface 162 of the sliding portion 157 is formed with three arcuate recesses 164 which are equiangularly spaced apart from each other by 120°. These arcuate recesses 164 are provided in order to make the piston 150 into engagement with each wedge 144 incorporated into the body 140. That is, after the wedges 144 are incorporated into the body 140, the piston 150 is inserted into the enlarged-diameter center bore 141 of the body 140 in such a way that the arcuate recesses 164 are in opposed relationship with respective engaging projections 148 of the wedges. After the piston 150 is completely inserted into the enlarged-diameter center bore 141 of the body 140 in the manner described above, the piston 150 is rotated through 60° so that the engaging projections 148 of the wedges 164 are made into engagement with respective engaging grooves 163, whereby the piston 150 can be made into engagement with each wedge 144. Of course it is possible to remove an adapter 165 which is joined to the rear end of the enlarged-diameter center bore 141 of the body 140 for mounting the body 140 on a spindle (not shown) and to incorporate each wedge 144 joined to the piston 150 into the body 140. A cover 166 is fitted into the reduced-diameter center bore 158 and made into slidable contact with the inner peripheral surface of the annular projection 159 of the piston 150. Next the mode of operation of the first embodiment with the above-described construction will be explained in detail below. When the piston 150 is pulled to the left in Fig. 5 by means of a draw bar (not shown), the pulling force is transmitted through the engaging groove 163 and the engaging projection 148 to each wedge 144 so that a pair of wedge main bodies 146 on both sides of the wedge 144 are guided by the sliding holes 142 and are displaced to the left. As a result, the top jaw 155 securely joined to the master jaw 120 can firmly hold the outer peripheral surface of a workpiece. In case of machining a workpiece held by the precision chuck in accordance with the present invention, the sliding surfaces 167 of the wedge portions 147 force the sliding surfaces 168 of the wedge grooves 123 of the master jaw 120 radially inwardly, but in this case, the sliding surfaces 169 of the wedge main bodies 146 supporting the wedge portions 147 are supported by the sliding surfaces 170 of the sliding hole 142 of the body 140, whereby an outer peripheral bearing surface is defined. From the standpoint of dynamics, the force R for causing the displacement of the wedge portion 147 produced by the pulling force of the piston 150 is exerted in the closed direction of the master jaw 120 while the reaction force P having the same magnitude and acting in the opposite direction is received by the wedge main body 146. In other words, the wedge main bodies 146 are subjected to the moment M, tending to rotate, but this rotation is effectively prevented by the base portion 145 integral with the wedge main bodies 146. Therefore the sliding surfaces 169 of the wedge main bodies 146 are received by the sliding surfaces 170 of the sliding holes 142 and the wedge main bodies 146 which are prevented from being displaced even when they are subjected to the torsional moment M can receive the force tending to cause the master jaw 120 to close as shearing stresses. On the other hand, when the piston 150 is pushed to the right in Fig. 5, the pushing force is transmitted through the engaging groove 163 and the engaging projection 148 to each wedge 144 as described above so that the wedge main bodies 146 on both sides of the wedge 144 are guided by the sliding hole 142 to be displaced to the right. More particularly, the sliding surfaces 171 of the wedge portions 147 of the wedge main bodies 146 slide over the sliding surfaces 172 of the wedge grooves 123 of the master jaw 120, whereby they are displaced relative to each other so that the master jaw 120 forced radially outwardly due to a wedge action. Therefore the top jaw 155 securely joined to the master jaw 120 can grip the inner peripheral surface of a workpiece. In case of machining a workpiece whose inner peripheral surface is securely gripped by the precision chuck in accordance with the present invention, the sliding surfaces 171 of the wedge portions 147 press radially outwardly the sliding surfaces 172 of the wedge grooves 123 of the master jaw 120, but the sliding surfaces 173 of the wedge main bodies 146 are supported by the sliding surfaces 174 of the sliding hole 142 of the body 140, whereby an inner peripheral bearing surface is defined. From the standpoint of dynamics, the force Ra which is produced by the pulling force of the piston 150 and which causes the wedge portion 147 to displace itself is exerted in the direction in which the master jaw 120 is opened while the reaction force Pa having the same magnitude and acting in the opposite direction is received by the wedge main body 146. In other words, the wedge main bodies 146 are subjected to the torsional moment Ma so that they tend to rotate, but their rotation is effectively prevented by the base portion 145 formed integral with the wedge main bodies 146. Thus, as in the case of the torsional moment M, even when the wedge main bodies 146 are subjected to the torsional moments Ma, they can receive as shearing stresses the force tending to open the master jaw 120. Therefore the deflection of the wedge main body 146 due to the shearing stresses acting thereon occurs only in the spacing between the master jaw 120 and the body 140. It follows therefore when the wedge main body 146 is given a sufficient dynamic rigidity in this spacing, the deflection of the wedge main body 146 can be eliminated completely. When the body 140 supports the wedge 144, it is preferable to use a beam construction which supports a load at both ends thereof so that the load which produces the force causing the master jaw 120 in the radial direction is supported at fulcrum points in the body 140 at both the axial ends of the master jaw 120. In the first embodiment, the piston 150 and the wedge 144 are fabricated as separate component parts. The reason is as follows. The portions of the body 140 in opposed relationships with the arcuate recesses 164 of the piston 150 can be radially inwardly extended and the radially inwardly extended portions can be further extended in the axial direction so as to be joined with the adapted 165. As a result, as compared with the prior art chucks in which the piston and the wedge are formed integral, the body 140 can be increased in rigidity and can be made light in weight. In case of the wedge 144 in the form of a fork end in which a pair of wedge main bodies 146 are formed integral with the base portion 145 as described above, the torsional moments acting on the two wedge main bodies 146 act on the base portion 145 as a couple so that when the strength of the joints between the base portion 145 and the wedge main bodies 146 is increased to such a degree sufficient to withstand such couple, the high-precision and high holding force hitherto unobtainable by the prior art chucks in which a pair of wedge main bodies and a base portion are not made into a unitary construction can be obtained. Various modifications of the fork-end-shaped wedge main body 146 which can attain the above-described function and effects, may be considered. For instance, as shown in Fig. 11, wedge main bodies 180 and wedge portions 181 extended therefrom, respectively, can be machined from a cylindrical workpiece 182 indicated by an imaginary line. Furthermore, as shown in Fig. 12, a wedge portion having a trapezoidal cross sectional configuration may be extended from a wedge main body 183 having a semi-elliptical cross sectional configuration. Second Embodiment, Figs. 13-15 Figs. 13-15 shows a second embodiment of a precision chuck in accordance with the present invention which is a modification of the first embodiment described above. The second embodiment is characterized in that the edge 144 and the piston 150 are integrated into a unitary structure, thereby providing a jaw-action body 185. The jaw-action body 185 has a wedge 186 which, as in case of the first embodiment, has a pair of opposing wedge main bodies 187 each of which is formed with a wedge portion 188. Referring next to Fig. 16, the fitting construction of a wedge main body 190 which can further enhance the effects, features and advantages of the present invention will be described. The wedge main body 190 has a semi-circular cross sectional configuration and a wedge portion 191 having an equilateral trapezoidal cross sectional configuration is extended inwardly from the wedge main body 190. A master jaw 192 is formed with a guide groove 193 which has an equilateral trapezoidal cross sectional configuration and into which is slidably fitted the wedge portion 191. Each of sliding holes 195 of the body 194 has a semi-circular cross sectional configuration so that the wedge main body 190 can be slidably fitted therein. The above-described construction has an advantage in that when the spacing between the master jaw 192 and the wedge portion 191 is same as that of the fourth embodiment described above, a play in the directions in which the master jaw 192 is opened and closed can be reduced due to the inclined sides of each trapezoid. In addition, the wedge main body 190 semi-circular in cross section is made into intimate contact with the curved wall surface of the sliding hole 195 so that the lateral displacement of the wedge portion 191 can be prevented. Importantly, when the forces in the opening or closing direction of the wedge main bodies 190 are exerted on the wedge portions 191, they act on the pressure receiving surfaces of the guide grooves 193 of the master jaw 192 and the reaction forces from the centers of the pressure receiving surfaces 196 act in the directions indicated by the arrows S and are received by the upper arcuated surfaces of the curved wall surfaces of the sliding holes 195. As a result, the wedge main body 190 has a stronger rigidity to withstand the reaction. In addition, when the reaction force passes through the center of the curved wall surface of the sliding hole 195; that is, when the arrow S passes the center of the curved surface, the reaction force becomes perpendicular to the upper arcuate surface so that no torsional moment acts on the wedge main bodies 190. As a consequence, no couple acts on the base portion of the wedge main body 190. This suggests that when, instead of the inclined lateral sides of a trapezoid, the wedge main body 190 has a curved surface coaxial with the curved surface of the sliding hole 195, a wedge action can be further enhanced. In the construction shown in Fig. 16, the wedge portion 191 is extended from the wedge main body 190 and the guide groove 193 is cut into the outer surface of the master jaw 192, but it is understood that the same effects and functions can be attained even when the guide groove 193 is cut into the wedge main body 190 while the wedge portion 191 is extended from the master jaw 192.

Claims: A precision chuck comprising a body (140) of unitary construction; a plunger (300) being movable forward and rearward in the axial direction of the body (140); a plurality of jaws (120) being movable inward and outward in the radial direction of the body (140) in response to a relative axial movement of the plunger (300), in which body wedges (144) are operatively connected to the plunger (300) for a movement in axial direction, each wedge (144) providing guide surfaces parallel to the axial direction and guide surfaces inclined to the axial direction; whereby jaw bodies (122) are operatively connected to the wedge for movement in radial direction of the jaws (120), the jaw bodies (122) having forward radial guide surfaces (151) and rearward radial guide surfaces (152), and inner and outer axially inclined guide surfaces engaging the inclined guide surfaces of the wedges; first guide means (142) are formed in axial direction on the body (140) in order to guide and move the body wedges (144) forward and rearward in axial direction, each first guide means (142) having both outer axial guide surfaces (170) and inner axial guide surfaces (174); and second guide means (143) are formed in radial direction on the body in order to guide and move the jaw bodies (122) inward and outward in radial direction, each second guide means having both forward radial guide surfaces (255) and rearward radial guide surfaces (256) and that the engaging portions between the inclined guide surfaces of the body wedge (144) and the corresponding inclined surfaces of the jaw (120) are always located within the range of the axial length of the parallel guide surfaces of the body wedge (144) in any operational position, and the first guide means (142) are formed on the body over the full range of the axial movement of the body wedge (144) whereby the parallel guide surfaces of the body wedge (144) are always supported in its full length by the first guide means (142) of the body (140), characterized in that the axial length of the inclined guide surfaces of the body wedge (144) is so much larger than the axial length of the corresponding inclined guide surfaces of the jaw (120) that the guide surfaces of the jaw (120) engage the guide surfaces of the body wedge (144) over its full length in any operational position. A precision chuck as set forth in claim 1, wherein a pair of the inclined guide surfaces of the body wedge are formed with a single engaging construction for engagement with a pair of the inclined guide surfaces of the jaw body. A precision chuck as set forthin claim1, wherein the two of the inclined guide surfaces of the body wedge are formed with multiple engaging construction for engagement with two pairs of the inclined guide surfaces of the jaw body and for arrangement to hold the jaw body. A precision chuck as set forth in claim1, wherein the body wedge is in the form of a fork-end in which a pair of wedge guides are extended from a base portion. A precision chuck as set forth in claim 1, wherein the plunger is in the form of unitary construction not to separate the body wedge from the piston. A precision chuck as set forth in claim 1, wherein the plunger is fabricated from separate component parts to separate the body wedge from the piston. A precision chuck as set forth in claim1, wherein the body wedge is provided with two pairs of parallel guide surfaces and a pair of inclined guide surfaces. A precision chuck as set forth in claim 1, wherein the first guide means formed in the body is in the form of a blind hole whose bottom is spaced apart by a suitable distance from the front portion of the body. A precision chuck as set forth in claim 1, wherein the engaging portions which engage the body wedge with the jaw body are in the form of uneven construction in which one is concave and the other is convex. A precision chuck as set forth in claim 1 or claim 9, wherein the engaging portions which engage the body wedge with the jaw body are in the form of uneven construction with trapezoidal cross sectional configurations. A precision chuck as set forth in claim 1, wherein the body wedge is made of a cylindrical workpiece. A precision chuck as set forth in claim 1, wherein the body wedge is mounted at a position which is radially outwardly of the body and at which the wall thickness strength is approximately hope one half of that of the body.

Inventors: KUROGI YOSHIHITO, SAWAGUCHI TATSUEI, KUROGI, YOSHIHITO, SAWAGUCHI, TATSUEI
Applicants: KITAGAWA IRON WORKS CO, KABUSHIKI KAISHA KITAGAWA TEKKOSHO
Application year: 1986
Main classification: B23B31
IPC codes: B23B31