Abstract: This invention relates to improvement of a chuck unit for machine tools consisting of main body, plunger, and master jaw. In a chuck where the master jaw and plunger engagement part constitutes an inverted T shape in cross section, slide surfaces of engagement between the wedge part of the master jaw and the plunger are formed into circular arc shape.

Abstract: A lock ring device for locking the soft jaws of a lathe chuck or the like for holding the jaws during the machining thereof to fit a workpiece to be held by the jaws, the device being adjustable to adjust the jaws in the locking position for the exact amount of metal removal desired.

Abstract: This invention provides a chuck for a glassworking lathe which includes a chuck body rotatable with a drive spindle nose about a longitudinal axis and a handwheel rotatable about the same longitudinal axis. A locking device is provided for releasably locking the handwheel to the chuck body for unitary rotation of the handwheel with the chuck body. A spiral gear or scroll is fixed to the handwheel to define a radially extending path of spiral movement relative to a longitudinal axis upon rotation of the spiral gear. A plurality of jaw base members include spiral gear grooves for meshingly engaging the spiral gear, are angularly spaced about the axis and are movable radially with respect to the axis upon rotation of the spiral gear engaging the gear grooves formed in the bottom of each of the jaw base members.

Abstract: The jaws of the chuck include a base jaw and a separate, releasable mounting jaw. These two jaw components are connected by at least one shaft which is guided with male-type screw threads in its one end in female-type screw threads of the base jaw. The other end has a lock head which has a projecting lock shoulder, and which lock head can engage in axial direction into a lock retainer in the mounting jaw, when the shaft has been rotated into the position corresponding to the unlocked condition. When the shaft has been rotated into the position which corresponds to the locked condition, it can engage with its lock shoulder in a dovetail formation in axial and positive locking manner. The shaft is further shaped with gear teeth which can operate in the manner of a pinion. In the apparatus there is also provided a control bolt extending transversely to the axis and guided and adapted to be shifted in its longitudinal direction in the base jaw.

Abstract: It has been hitherto customary durig machining of workpiece, such a grinding of gear wheels, to slip a roller cage over the gear wheel. The chuck jaws of the chuck then hold the workpiece by way of the rollers in a roller cage. The time concuming operation is made superfluous by a holding ring which is mounted in the chuck. The holding ring has openings near the chuck jaws, and also has in this region fixedly installed roller-cage-type segments. Input guides at the holding ring allow quick, safe and secure exchange of the workpieces.

Abstract: A quick changing jaw carrier assembly for mounting a top jaw. The jaw carrier assembly includes a main jaw carrier slidably confined for radial movement within a slot of a rotatable housing. An auxiliary jaw carrier or locking wedge is radially slidably mounted on the main jaw carrier. The auxiliary and main jaw carriers define radially opposed wedges for defining a dovetail structure which lockingly engages a similar such structure on the top jaw. The auxiliary jaw carrier is spring urged outwardly into a jaw-engaging position, and can be manually moved inwardly from this position when release of the jaw is desired. A manually-controlled locking cam is rotatably supported on the main jaw carrier and can be rotatably displaced into a locking position wherein the locking cam projects radially beneath a shoulder formed on the auxiliary jaw carrier when the latter is in its jaw-engaging position.

Abstract: In an arrangement for coupling a false jaw to a master jaw of a chuck, wherein a positive locking is effected by a radial displacement, the master jaw is provided with an extension having a stop surface and a projection. The false jaw has a recess for receiving the extension and a relief shoulder and is guided in the direction of rotation. Due to this arrangement, the false jaw is well supported and highly stable, so that strong forces can be transmitted, and a high repetitive accuracy in chucking is obtained.

Abstract: A chuck centered on an axis and having a plurality of jaws each displaceable radially of the chuck axis is usable in combination with a drill bit having a shank formed with respective grooves each having axially extending and angularly directed flank surfaces engageable with the jaws to rotationally link the bit to the chuck. Each jaw is substantially symmetrical to a respective jaw plane extending substantially radially of the chuck axis. In addition each jaw is formed with a pair of angularly spaced teeth substantially symmetrically flanking the respective jaw plane and each having a respective inwardly directed edge and an outer tooth surface extending radially back therefrom and angularly away from the respective jaw plane.

Abstract: A three-jaw chuck of a lathe is adapted to rectangular or square-shaped work pieces by a U-shaped adaptor placed on one of the jaws. The adaptor may be adjustable as to the distance between the jaw tip and the support surface for the workpiece. Alternatively, a set of adaptors of differing thickness can be provided for purpose of selection on a case-by-case basis.

Abstract: To firmly retain the jaw of a lathe chuck against movement it is provided with a locking mechanism having a pair of locking members arranged to bear on the chuck face, and an actuating means adjustably mounted on the jaw so as to force the locking members against the chuck face for locking the jaw in a fixed position relative to the chuck.

Abstract: A self-centering chuck with adjustable and replaceable jaws includes false jaws which are slidable radially in corresponding recesses in an annular body of the chuck through the action of a rod coaxial with the chuck itself. The jaws, each of which has tangential teeth facing the corresponding false jaw, are also slidable in the recesses. In each of the false jaws is mounted a peg slidable parallel to the axis of the chuck. The peg has teeth for engagement with a respective jaw. Each peg has a transverse groove facing radially outwardly of the chuck. This groove is engaged by an eccentric which is rotatable in the false jaw about a radial axis parallel to the direction of sliding of the false jaw. This eccentric has a formation engageable by a key or similar operating tool for rotating it in order to disengage and re-engage the peg relative to the corresponding jaw.

Abstract: In a chuck for use in a drilling device, such as a hammer drill, capable of performing rotary or rotary/percussion drilling, clamping jaws are provided to secure a tool in the drilling device. The clamping jaws each have a convex surface transverse to the chuck axis and with the surface directed inwardly toward the axis. The more radially inward portion of the convex surface has a V-shaped notch extending in the axial direction of the chuck. The notch forms a pair of spaced edges which grip the surface of the tool secured in the chuck so that the tool can be reliably rotated.

Abstract: A center chuck assembly for rotatably supporting the end of a cylindrical workpiece comprises a shaft rotatable in a mounting pipe to be mounted on a receiving member and having an operating flange and a disc formed on the outer end thereof. The disc has a spiral groove on the end surface thereof. A chuck holding member having chuck members slidably fitted within holes formed radially in the chuck holding member, is rotatably fitted on the disc of the rotating shaft. The chuck members have teeth on one side thereof, and these teeth engage with the spiral groove on end surface of the disc. By rotating the operation flange relative to the chuck holding member, the chuck members are caused to project outwardly by means of engagement of said teeth and spiral groove and to abut the inside surface of the workpiece at a position spaced from the end of the workpiece, thereby supporting the workpiece securely. By using this center chuck assembly, end surface of the workpiece can be machined easily in one process.

Abstract: A drill chuck for a hammer drill apparatus or the like having a plurality of clamp jaws advanceable to and retractable from a chuck drill axis so as to be able to grasp and hold a drill, wherein each of the clamp jaws is advanced into and retracted from a chuck opening in the chuck in a feed channel directed toward, and preferably perpendicular to, the chuck drill axis and further oriented so that the clamp jaws engage and hold the drill in the chuck opening when advanced in the channels, each of the feed channels being conformed so that each of the clamp jaws fits movably, but sufficiently tightly, therein so that drilling dirt does not penetrate between the clamp jaws and the surfaces of the feed channels, and the drill chuck is provided with a plurality of open cleaning passages connecting the interior wall of the chuck opening adjacent a mouth of one of the feed channels to the outside through the chuck.

Abstract: A jaw for chucking devices, especially multiple-jaw chucks of machine tools, for example, for chucking workpieces having surfaces curved in only one direction, especially workpieces having round chucking surfaces. The contact face of the jaw is provided on a chucking element consisting of hard but flexible material to which the chucking force is applied in at least one line parallel to the curved surface of the workpiece.

Abstract: An apparatus is provided which enables the jaws of a chuck 10 to be removed from and inserted into jaw-ways 12, 13, 14 using a conventional workpiece handler, rather than a sophisticated and highly accurate dedicated jaw handling mechanism. A conventional workpiece handler cannot position a jaw to close tolerances but this problem is overcome by using a guide shoe 17 which can receive a jaw from the workpiece handler in any one of a range of positions and then accurately guide the jaw into one of the jaw-ways 12, 13, or 14.A mechanism 16 is provided for releasing the jaws from the jaw-ways, and for re-locking the jaws in position.

Abstract: An improved chuck assembly for a lathe comprises a housing member serving as a base, first holding means movably connected to the base for selectively radially gripping the side surface of a workpiece, and second holding means connected to the base for axially engaging an end surface of such workpiece. The second holding means is located generally centrally of the first holding means, the first holding means being movable both radially and longitudinally to clear the end of the workpiece without removal of the chuck.

Abstract: To check the operating conditions of a power chuck, compressed air is supplied to the contact surfaces of the clamping jaws and/or of the workpiece to be clamped. Air passages are provided in the chuck body which open into the contact surfaces. The escaping air makes it possible to find out whether the contact is planar, and thus whether the clamping is exact.

Abstract: A dental handpiece grips a removable dental tool by teeth within the end of a resilient quill carried within the spindle of said handpiece and when rotated in one direction by the handpiece turbine providing an axial force on the dental tool tending to draw the tool axially into the quill despite any opposite pull due to teeth on the dental tool.

Abstract: The invention relates to a screw joint of plastic for leading-in, leading-through, sealing and pull-relieving cables, lines or other thread-like elements (cable screw joint) comprising an intermediate connection piece with a sealing body inserted therein, and a box nut. The intermediate connection piece is provided with clamping tongues formed integrally therewith and extending coaxially thereto, which clamping tongues retain between them the mounted cable. The arrangement of the clamping tongues is such that when the box nut is turned at least one, preferably more clamping tongues distributed evenly over the circumference are urged inwardly in a selective manner and out of the remaining annular clamping tongue arrangement to exert upon the cable, preferably through the interposed packing, a deforming pressure providing positive protection against torsion of the cable relative to the cable screw joint.

Abstract: A wear pad assembly is provided for machine tools or the like in the form of a generally frusto-conical pad member having a support surface on its base to receive a work piece and a base having a frusto-conical opening supportingly receiving the apex end of the pad member and a threaded attachment member removably connecting the apex end of the pad member with said base. The support surface is preferably knurled or otherwise toothed and hardened to hold a work piece against slipping.

Abstract: A chuck jaw changer is disclosed as mounted on the headstock (24) of an N/C lathe (22) for automatically changing the set of gripping jaws (32) of a quick change chuck (28) on a work spindle (26) with any of other interchangeable sets of gripping jaws (32') being held by a rotary, indexing jaw magazine (34). The jaw magazine has formed therein several jaw grooves (150) each for holding one set of gripping jaws (32'), or the jaw set (32) withdrawn from the chuck, slidably engaged therein in a row. An indexing mechanism (35) revolves the jaw magazine relative to the machine tool for bringing any of the jaw grooves into line with that one of radial jaw guideways (54) of the chuck which is being held in a prescribed jaw change position on the work spindle. A jaw transfer mechanism (36) operates for successively transferring the set of jaws from the chuck into an empty jaw groove in the jaw magazine, and a different set of jaws from the jaw magazine to the chuck.

Abstract: The chuck disclosed has three radially movable jaws for gripping and releasing a workpiece. The jaws are displaced radially by means of a draw-bar actuated puller plate coupled to the inner ends of inclined, radially extending rods on which the jaws are mounted. The puller plate is swivelly coupled to the drawbar and to the jaw rods to enable the jaws to firmly grip a workpiece around a surface which is not concentric to a previously machined centering surface on the workpiece and by means of which the workpiece is positioned on the chuck. Means are provided for optionally preventing swiveling movement of the puller plate.

Abstract: A workpiece chuck has a plurality of support blocks adapted to be mounted on the front face of the chuck body in circumferentially spaced relation and at various locations spaced radially different distances from the central axis of the chuck. Within each support block a jaw rod is arranged for sliding movement along an axis inclined at an acute angle to the central axis of the chuck. A coupling interconnects the inner end of each jaw rod with an axially displaceable puller plate within the chuck body. The front plate of the chuck and the puller plate are formed with registering, radially elongated openings to permit radial adjustment of the jaw rods and to enable them to be retracted outwardly from the chuck body together with their support blocks.

Abstract: A top jaw adapted for mounting on and attachment to the master jaw of a conventional work holding chuck and simultaneously during attachment thereof to be located radially against a fixed stop by a double T-nut of unique configuration, the latter being movable by an actuator screw in T-slots provided in the jaws, one portion of the T-nut and the complementary T-slot in the top jaw in which it is mounted being inclined with respect to and sloping toward the interface between the top and master jaws so that tightening of the T-nut by the actuator screw forces the top jaw radially against the stop and simultaneously axially against the mating surface of the master jaw, the taper angle of T-nut and the lead angle of the screw threads mutually cooperating to lock the top jaw on the master jaw in use.

Abstract: To firmly retain the jaw of a lathe chuck against movement it is formed with a transverse passageway or hole through it about midway of its length, a U-block is inserted in it in an inverted position so its legs will bear on the chuck face and a bolt is threaded in the jaw directly above the U-block so it will bear on the block and force it against the chuck face.

Abstract: A chuck with T-slots to receive slot blocks for the attachment of stops or rests on the chuck body or on clamping jaws guided for radial movement within the chuck body by at least one attachment screw which engages into a slot block. In order to prevent throwing off of the clamping jaws even if the attachment screws are not properly tightened, the T-slot opens at its radially inward end into a continuous bore having a diameter corresponding to the width of the slot at the base of the slot and at least the base of the slot terminates at a radial distance from the outer periphery of the chuck body at the radially outward end of the slot or the base of the slot is inclined away from the face of the chuck in a direction toward the outer periphery.

Abstract: To firmly retain the jaw of a lathe chuck against movement it is formed with a transverse slot in its bottom, a key-like block is inserted in the slot and has a pair of leg members arranged to bear on the chuck face, and a screw member is threadedly mounted in the jaw directly above the block so that it will bear on the block and force the leg members thereof against the chuck face.

Abstract: A top jaw for attachment to a rotary chuck, with inserts removably secured to a base, constructed to facilitate changing inserts with automated equipment. Slidably engageable pins and slots on the base and insert require positioning and removal of the insert with two directions of relative movement and thereby inhibit separation of the insert from the base from forces applied other than is a prescribed direction and sequence. The insert is releasably held to the base by detents.

Abstract: A chuck has a chuck body rotatable about an axis, a plurality of jaws radially displaceable on the body and each having a radially inwardly directed workpiece-engaging face, and an axially displaceable operator linked to the jaws to radially displace same relative to the chuck body. Respective transducers on the chuck body are connected to the jaws for generating a signal proportional to a parameter of the respective jaw. These signals are transmitted from the chuck body to a stationary signal receiver adjacent the chuck body wholly without physical contact with the signal transmitter. Similarly, a stationary energy transmitter adjacent the chuck body transmits energy and a receiver on the chuck body receives the transmitted energy wholly without physical contact with the energy transmitter and powers the signal transmitter therewith. The transducers can be position or force transducers, for instance constituted by strain gauges or linear potentiometers.

Abstract: To firmly retain a jaw of a lathe or like chuck against movement it is formed with a transverse passageway or hole through it about midway of its length, a U-block is inserted in it in an inverted position so its legs will bear on the chuck face and a bolt is threaded in jaw directly above the U-block so it will bear on the block and force it against the chuck face.

Abstract: An apparatus is disclosed for a chuck with a guide roller assembly useful in automatic and semi-automatic machining operations. This apparatus provides for a chuck with a guide roller assembly that will prevent the end of the pipe from striking the jaws of the chuck as the pipe is moved into position to be gripped by the chuck and that will exert a vibration dampening force on the pipe while the pipe.Also disclosed is a plurality of rollers that are mounted on the jaws of the chuck on the side of the jaws toward which the workpiece travels as it is moved into position to be gripped by the chuck and that are made of an elastomeric material and positioned to engage the workpiece ahead of the jaws of the chuck so that the rollers will be compressed as the jaws of the chuck move into engagement with the workpiece to provide a vibration dampening force on the pipe on the side of the chuck away from the machining operations.

Abstract: An improved chuck collet in which the elements of the collet, namely the jaw segments, the mounting base, and the interconnecting flexible members, are separate elements thus permitting a selection of materials for the elements to give optimum operating characteristics to the assembly at economical costs.

Abstract: A method and a clamping assembly for securing rock bit sections during welding. The assembly has a chuck jaw that is supported by metal rods, which give the assembly enough resiliency to conform to the shape of the rock bit and which keep the chuck jaw parallel to the base so that the point of engagement between the chuck jaw and the rock bit section remains constant.

Abstract: An adjustable collet is provided comprising a step collet, a plurality of machinable and removable jaws, and means for interlocking the jaws with the step collet. The interlocking means comprise counter-bored and threaded holes spaced on the face of the collet, and hollow bosses projecting from one surface of the jaws and aligned with counter-bored or counter-sunk holes on the opposite surface, the interlocking means being effected by mating the jaw bosses with the holes in the collet face and by engaging screws passing through the holes and bosses in the jaws to the threaded holes in the collet face. To further increase the capacity of the collet, extension bars are utilized that incorporate the above-described interlocking means.

Abstract: A multiple-jaw chuck comprises a housing and a drive cylinder driven parallel to the longitudinal axis of the housing and driving a plurality of chuck jaws towards and away from the housing longitudinal axis. The chuck includes one or more axially-extending pins for each chuck jaw fixed to the drive cylinder at an acute angle to the housing longitudinal axis. Each chuck jaw includes a bore for each pin and formed at the same acute angle, such that each chuck jaw is driven radially towards and away from the longitudinal axis of the housing when the drive cylinder is driven parallel to the housing axis. Each chuck jaw further includes an inner drive arm coupled to the drive cylinder, and an outer workpiece-engaging arm, each of the drive arms being of substantially cylindrical configuration and movable in a bore of corresponding cylindrical configuration formed in the housing.

Abstract: A fluid-actuated type hollow power chuck has a hollow cylindrical chuck body with a forward part of larger outer diameter and a rearward part of small outer diameter. A cylinder body of a hollow cylindrical shape is secured to and around to the outer surface of the rearward part of the chuck body so as to form an annular cylinder chamber. A piston slidable in the cylinder chamber to operate the jaws has a piston sleeve extending rearward therefrom between the chuck body and the cylinder body, the displacements of the piston sleeve being detected at points rearward of the cylinder body by proximity switches installed in a ring disposed to the rear of the cylinder body, whereby displacements of the jaws are indirectly indicated by the switches.

Abstract: This invention pertains to an auxiliary jaw which is adapted to be affixed to a movable member and as this movable member is advanced to and from a workpiece to grip and hold this workpiece when and while the auxiliary jaw is advanced. This auxiliary jaw includes a pivoted jaw member carried by a support member which is preferably secured to the movable member by cap screws. The pivoted jaw member engages the surface portion of the workpiece in local areas as it exerts a gripping force urges the workpiece toward the support surface. Three configurations of jaw assemblies are shown. Each has a pivoted jaw with one configuration supporting the workpiece above the pivoted jaw. In a second configuration the support as a pin means is below the pivoted jaw and in yet a third configuration the pivoted jaws are movable toward and to a support disk for multiple workpieces. Soft jaws, hardened jaws and bias means may be used to bring the pivoted jaw to the desired condition.

Abstract: Three gripping jaws are slidably engaged in respective radial guide grooves in the front face of an annular jaw carrier for holding work to be machined. Each gripping jaw has a wedge integrally projecting rearwardly therefrom. The wedge is of T-shaped cross section, including a web extending radially of the jaw carrier and a flange at the inner end of the web. Slidably mounted in the jaw carrier for axial movement therein, a plunger has undercut wedge grooves for slidably receiving the flanges and parts of the webs of the respective wedges, causing the radial motion of the gripping jaws by a wedging action upon axial motion of the plunger. A pair of opposed overhanging portions formed by each undercut wedge groove in the plunger are caught between the jaw carrier and the flange of one of the wedges.

Abstract: A chuck has a chuck body rotatable about a chuck axis and subdivided along a plane perpendicular to this chuck axis into a front chuck part and a rear chuck part integrally connected together. The rear chuck part is formed with a plurality of angularly spaced and radially extending rear T-section guide grooves opening axially forwardly at the plane and each having a pair of radially extending sides each in turn formed with a step extending parallel to and backwardly offset from the plane. The front chuck part is formed in axial alignment with the rear guide grooves with respectively angularly spaced and radially extending guide grooves opening axially forwardly. The front chuck has a backwardly facing planar face lying on the plane and forwardly closing the rear guide groove. Respective webs form the bases of the backwardly closed front guide grooves, and are formed with radially throughgoing apertures substantially smaller than the respective front guide grooves.

Abstract: According to the present apparatus work pieces such as railroad wheels are power clamped on a cone shaped inwardly facing side. In a first clamping step clamping areas are impressed into the side or surface of the work piece said clamping areas having a suitable inclination. In a second clamping step the actual power clamping is performed at these clamping areas. For this purpose a plurality of radially moving clamping jaws are arranged to carry at least one clamping tooth. Each clamping tooth in turn is adjustable in its position in an axial direction along its respective radially moveable clamping jaw.

Abstract: A lathe chuck jaw for a lathe chuck having a radially moving actuator which radially moves the jaw in to and out from the workpiece. A jaw base part is rigidly connected to the actuator. A jaw shoe part is rotatably attached to the base part. The shoe part has a workpiece-comforming surface which can hold the workpiece. The rotatable attachment of the shoe part allows it to match the general orientation of the workpiece, including a nonlongitudinal orientation due to a workpiece's imperfect shape.

Abstract: A chuck for lathes having a chuck body in which at least two clamping jaws which can be jointly actuated by a drive member are guided in radially displaceable manner, the jaws consisting in each case of a drive jaw part which is continuously in operative connection with the drive member and of a clamping jaw part which is guided for radial movement independently of the drive jaw part within the chuck body and can be connected in form-locked manner with the drive jaw part by a coupling piece arranged in the drive jaw part. The form-locked engagement of the coupling piece with the clamping jaw part can be eliminated via positive drive surfaces by a spring-loaded actuating member which is movable substantially radially and independently of other actuating members.

Abstract: According to the present method and apparatus work pieces such as railroad wheels are power clamped on a cone shaped inwardly facing side. In a first clamping step clamping areas are impressed into the side or surface of the work piece said clamping areas having a suitable inclination. In a second clamping step the actual power clamping is performed at these clamping areas. For this purpose a plurality of radially moving clamping jaws are arranged to carry at least one clamping tooth. Each clamping tooth in turn is adjustable in its position in an axial direction along its respective radially moveable clamping jaw.

Abstract: A rotatable carrier for holding kinescope faceplates during processing includes a support plate having radially extending retention slots. Object retainers are arranged to slide in the slots and hold the object being processed. The retainers are biased outwardly away from the axis of rotation by biasing means. A tensioning band urges the retainers inwardly toward the axis of rotation so that centrifugal force acts against the tensioning bands rather than the springs.

Abstract: A soft chuck jaw comprising a hardened jaw body having a wedge locking means thereon and an insert of soft expendable material retained therein.

Abstract: A mechanical concentric support device for use on machine tools such as lathes, precision grinders and the like, for either internal or external engagement of the workpiece by radially extensible support shafts driven by a scroll mechanism. The key connection for the scroll mechanism is located on one of the circular faces of the device to permit close-fitting internal support of cylindric workpieces, and adapters are shown for both internal and external gripping of workpieces of a wide range of diameters both larger and smaller than the diameter of the support device.

Abstract: A lathe chuck has a chuck body rotatable about an axis and formed with a plurality of angularly spaced and radially extending inner guides and with a plurality of angularly spaced and radially extending outer guides. Each of the inner guides in turn has an axially forwardly directed and radially extending blocking surface and an axially forwardly opening recess at the respective blocking surface. Inner jaws parts are radially displaceable in the chuck body in the inner guides and outer jaw parts projecting axially from the chuck body are radially displaceable therein in the outer guides. An operating element engages the inner jaw parts and jointly radially displaces them between radially inner and radially outer positions.

Abstract: A lathe chuck has a chuck body rotatable about a chuck axis and formed with a plurality of angularly spaced and radially extending inner guides receiving respective inner jaw parts and with a plurality of angularly spaced and radially extending outer guides receiving respective outer jaw parts. The inner jaw parts can be synchronously radially moved to open and close the chuck. Respective coupling members are provided between the inner jaw parts and the respective outer jaw parts and are rotational about respective coupler axes extending radially of the chuck axis between coupling positions engaging both of the respective parts and coupling same together for joint radial displacement and angularly offset decoupling positions permitting relative radial displacement of the respective parts. Locking elements are operatively engageable between the inner jaw parts and the chuck parts for blocking radial displacement of the inner jaw parts except when the respective coupling members are in the coupling positions.

Abstract: A chuck assembly for rigidly gripping an elongated workpiece, and particularly concrete reinforcing bars, is disclosed. The chuck assembly is designed for use in a machine tool, such as a thread mill, to enable threading of the ends of reinforcing bars. The chuck assembly includes jaws that are formed to engage the bar over a substantial length, preferably at least four bar diameters, and that are formed to provide a line contact engagement of the bar so as to dig into the bar ribs and provide high resistance to torsional forces. The jaw members are preferably tapered and actuated by a pair of complimentary wedge members mounted in sliding engagement with substantially the entire length of the jaw members. The chuck assembly is mounted in a two piece cast housing that is bolted together and formed with openings to permit debris to gravitate from the movable members of the assembly.