Chuck and method for manufacturing same

A chuck includes a plurality of master jaws 20 that slide in the radial direction in the front surface of a body 10 in conjunction with slide of a plunger 40. The body 10 has a housing chamber 11 communicating with a plurality of keyways 13. The plunger 40 is fitted in the housing chamber 11. Each of the master jaws 20 includes a narrower part 21 and a wider part 22 fitted into an associated one of the keyways 13, and a wedge 23 connected to the plunger 40. The wider part 22 has a flat wider sliding surface 22b radially outside the wedge 23. Each of the keyways 13 has a wider slid surface 14.

TECHNICAL FIELD

The present disclosure relates to a chuck that supports a workpiece and is used for a lathe, for example.

BACKGROUND ART

FIG. 1shows a cross-sectional structure of a known chuck of the type described above (an appearance structure is shown inFIG. 6). In order to support a workpiece with a rotation axis J coinciding with the chuck, a body100includes, on its front surface, a plurality of top jaws101aarranged like rays to slide in a radial direction. The top jaws101aare, together with T-nuts101c, detachably attached to master jaws101bin the body100to slide in the radial direction.

As shown inFIG. 2, each master jaw101bis assembled to the body100, while being fitted in a keyway102extending in the radial direction and having a T-shaped cross section. In addition, each master jaw101bis connected to a plunger103in the body100so as to slide in the radial direction in conjunction with an axial slide of the plunger103.

Specifically, once the plunger103slides rearward, the master jaws101bslide radially inward. Accordingly, a workpiece is supported radially inside the top jaws101a. Once the plunger103slides forward, the master jaws101bslide radially outward. Accordingly, the support of the workpiece is released.

As shown inFIG. 3, a pair of key protrusions104and104protrude from respective sides of each master jaw101b. These key protrusions104and104have sliding surfaces105(dotted in the figure) facing forward and rearward. As shown inFIG. 2, these sliding surfaces105are in surface contact with the keyway102in the axial direction. In each master jaw101b, there are gaps S between the keyway102and the side of each key protrusion104, between the keyway102and a step104aslightly protruding between the pair of sliding surfaces105and105facing rearward, and between the keyway102and each side of the step104a(i.e., without any surface contact).

A wedge-like protrusion (i.e., a wedge106) protrudes behind the radially inner end of each master jaw101b. This wedge106is configured to be fitted into a wedge-like groove in the plunger103. The wedge106includes a rib106asignificantly extruding in the radial direction to ensure strength.

Since the sliding surfaces105are required to have high dimensional accuracy and smoothness and are thus subjected to grinding processing. Specifically, as indicated by the arrows A inFIG. 4, a grinder of a grinding machine200that is positioned highly accurately is pressed onto the pair of sliding surfaces105and105facing rearward and is then controlled to slide in the sliding directions as indicated by the arrows B inFIG. 3. In this manner, the sliding surfaces105are ground so as to have predetermined dimensional accuracy and smoothness.

The pair of sliding surfaces105and105facing forward are ground similarly. Patent Document 1 discloses a chuck including similar master jaws.

CITATION LIST

Patent Documents

SUMMARY OF THE INVENTION

Technical Problem

As shown inFIG. 1, if a workpiece is supported radially inside the top jaws101a, a force acts, as a reaction force, on each top jaw101ain the direction indicated by the arrow M. Due to the rearward draw of the plunger103and a wedge effect, the wedge106receives a radially inward force as indicated by the arrow N. These forces cause strong moments acting on the master jaw101bas indicated by the arrows C inFIG. 1.

The master jaws101bare arranged like rays. Thus, when the master jaws101bsupport a workpiece, the moments of such forces act in the points corresponding to the locations of the master jaws.

By contrast, the known master jaws101bsuch as those described above are supported by the body100via the fitting parts having a relatively small contact area between the keyways102and the sliding surfaces105of the pair of key protrusions104and104protruding to respective sides of the master jaws. Such configuration tends to cause distortions or deformations in the key protrusions104, which may result in floating of the top jaws101aand give a negative influence on the support accuracy.

In the case of the known master jaw101b, the sliding surfaces105are ground in the sliding direction. The wedge106between the sliding surfaces105and105has a circumferential width that is narrower than the distance between the sliding surfaces105and105on both sides.

If the wedge106has a smaller width, the force acting on the body100from the plunger103as indicated by the white arrows inFIG. 5is concentrated in one circumferential direction, thereby causing distortions or deformations in the body100.

To address the problem, it is an objective of the present disclosure to provide a chuck capable of stably supporting a workpiece and less likely to cause distortions or deformations in master jaws or a body.

Solution to the Problem

The present disclosure relates to a chuck including a body and a plurality of jaws, plurality of jaws being positioned at a front surface of the body while supporting a workpiece with rotation axes of the chuck and the workpiece coinciding with each other.

The chuck includes: a plunger arranged inside the body with a center of the plunger coinciding with the rotation axes and configured to slide in an axial direction; and a plurality of master jaws each constituting one of the jaws and configured to slide in a radial direction in the front surface of the body in conjunction with the slide of the plunger.

The body includes: a plurality of keyways arranged like rays at equal intervals in the front surface and having a transverse section having a substantially inverted T-shape toward front; and a housing chamber at a center of the body to communicate with the plurality of keyways, the plunger being fitted in the housing chamber. Each of the master jaws includes: a narrower part fitted in a front portion of an associated one of the keyways and exposed to the front surface of the body; a wider part fitted in a rear portion of the associated one of the keyways and sliding along the associated one of the keyways; and a wedge protruding rearward from a radially inner end of the wider part and connected to the plunger.

The wider part has a flat wider sliding surface in an entire region radially outside the wedge, and each of the keyways has a wider slid surface that comes into surface contact with the wider sliding surface.

Unlike the chuck of the known art having the sliding surfaces only on both sides of the radially outer region of each wedge, this chuck has the flat wider sliding surface in the entire region radially outside each wedge. In addition, each of the keyways has the wider slid surface that is in surface contact with the wider sliding surface.

As a result, this chuck can receive strong forces that act on the master jaws by the surface contact between the wider sliding surface and the wider slid surface, each having a larger area. As a result, distortions and deformations are less likely to occur in the master jaws, and the accuracy in supporting a workpiece improves.

In one preferred embodiment, the wider sliding surface is slidable in both of the radial direction and a circumferential direction while being in surface contact.

In one preferred embodiment, the wedge has a greater width than the narrower part.

In one preferred embodiment, the plunger has, on an outer circumference of the plunger, a plurality of wedge housing grooves each having a transverse section having a substantially inverted T-shape toward radially outside and inclined so as to be closer to a center toward the front. The wedge includes: a sliding part fitted in a radially inner part of an associated one of the wedge housing grooves to slide along the associated one of the wedge housing grooves; and a loosely fitting sliding part fitted in a radially outer part of the associated one of the wedge housing grooves. The loosely fitting sliding part is housed inside the associated one of the wedge housing grooves so as not to come out of the plunger.

In one preferred embodiment, transverse ends of the sliding parts of the master jaws are arranged at substantially equal intervals in the circumferential direction.

In one preferred embodiment, transverse ends of the sliding parts of the master jaws are arranged in the circumferential direction at intervals at a central angle of about 60 degrees.

In one preferred embodiment, a method of manufacturing the chuck described above includes forming the wider sliding surface by finishing processing in a direction orthogonal to a sliding direction of the wider sliding surface.

Advantages of the Invention

The disclosed technique is less likely to cause distortions or deformations in a body or master jaws and thus allows highly accurate and stable support of a workpiece.

DESCRIPTION OF EMBODIMENT

An embodiment of the present invention will be described in detail with reference to the drawings. Note that the following description of the embodiment is merely an example in nature, and is not intended to limit the scope, applications, or use of the present invention.

FIGS. 6 and 7show a chuck1according to an embodiment. The chuck1has a thick, disk-like appearance and is attached to a machine tool2such as a lathe so as to rotate about a rotation axis J in a predetermined direction. During processing, the chuck1firmly supports a workpiece with the axes of the chuck and the workpiece coinciding with the rotation axis J.

In the description, the “rear” of the chuck1is attached to the machine tool2, and the “front” of the chuck1supports the workpiece. In addition, the “axial” direction corresponds to the direction in which the rotation axis J extends. The “circumferential” direction corresponds to the direction around the rotation axis J. The “radial” direction corresponds to the direction along the radius or diameter of the chuck with respect to the rotation axis J. In the radial direction, the center of the chuck1, that is, the rotation axis J is located “radially inside.” The outer circumference of the chuck1is located “radially outside.”

As shown inFIG. 8, the chuck1includes a body10, master jaws20, and a plunger40, for example. The body10includes, on its front surface, a plurality of (e.g., two or more in one preferred embodiment, three in this embodiment) top jaws30arranged circumferentially at equal intervals.

The body10and the master jaws20include a mechanism (i.e., a lubricant supply mechanism) for supplying a grease (i.e., an example lubricant) into the chuck1, which will be described later.

The master jaws20slide radially in the front surface of the body10. Each of top jaws30is, together with a T-nut31, removably attached to one of the master jaws20with bolts, thereby constituting a jaw. Each top jaw30may be integral with one of the master jaws20.

Each top jaw30may be in various shapes depending on the application and is in the shape of a cuboid in this embodiment. The radially inner end surface serves as a support for the workpiece. Alternatively, the top jaw30may have the support located radially outside so that a workpiece, such as a cylindrical body, is supported from the inside.

The body10is made of a metal member with a thick, disk-like appearance. The rear of the body10is fixed to a spindle of a machine tool (not shown) with mounting bolts. At a central part of the body10facing the rear, a cylindrical housing chamber11is open. The body10has, at the center of the front surface, a circular opening12that communicates with the housing chamber11. The front surface of the body10is a flat surface orthogonal to the rotation axis J.

The body10has, in the front surface, three keyways13arranged circumferentially at equal intervals. The keyways13extend like rays and radially outward from the periphery of the housing chamber11and pass through the body10between the outer peripheral surface of the body10and the housing chamber11. Each keyway13has a transverse section having a substantially inverted T-shape toward the front.

Specifically, each keyway13includes a front (i.e., a front slide13a) and a rear (i.e., a rear slide13b). The front is open to the front surface of the body10and has a relatively smaller width (which corresponds to the circumferential size, and the same applies hereinafter). The rear is located behind the front and continuous with the front, and has a relatively greater width.

The plunger40is fitted in the housing chamber11so as to slide in the axial direction, with the center of the plunger40coinciding with the rotation axis J. As shown inFIG. 8, the plunger40is a substantially cylindrical metal mass and has an outer peripheral surface that comes into surface contact with the inner peripheral surface of the housing chamber11and slides on the surface. The plunger40has, in the outer circumference, three wedge housing grooves41arranged in accordance with the locations of the keyways13.

Each wedge housing groove41has a transverse section having a substantially inverted T-shape toward the radially outside. Specifically, each wedge housing groove41includes a radially outer part (i.e., a loosely fitted slid part41a) and a radially inner part (i.e., a slid part41b). The radially outer part is open to the outer circumferential surface of the plunger40and has a relatively smaller width. The radially inner part is located inside the outer part and continuous with the outer part, and has a relatively greater width.

Each slid part41bhas, at both transverse ends, a pair of slid surfaces42and42facing each other in the radial direction. These slid surfaces42are ground to have high dimensional accuracy and smoothness.

Each wedge housing groove41is inclined so as to be closer to the center toward the front. Specifically, each wedge housing groove41is inclined at a predetermined angle so that the wedge housing groove41comes closer to the center in the radial direction with a decreasing distance to the front (i.e., with an increasing distance from the rear).

A cylindrical connector43is fixed to the rear of the plunger40. The plunger40is connected to a cylinder (not shown) via the connector43. Accordingly, the plunger40is controlled by the machine tool2so as to slide in the axial direction.

As shown inFIG. 8, each master jaw20is incorporated in the body10while being fitted in the associated keyway13and wedge housing groove41.FIGS. 9 and 10show a detailed structure of each master jaw20. The master jaws20are hard metal members.

The master jaw20includes a narrower part21, a wider part22, and a wedge23, for example. The narrower part21is fitted in the front slide13a(i.e., the front) of the associated keyway13to constitute the part exposed to the front of the body10. The wider part22is located behind and continuous with the narrower part21to constitute the part to be fitted into the rear slide13b(i.e., the rear) of the keyway13. The wedge23protrudes rearward from the radially inner end of the wider part22, is located in the housing chamber11, and constitutes the part to be connected to the plunger40.

The narrower part21is in the shape of a prism extending in the radial direction and has, in the part exposed from the body10, a transverse section having a substantially inverted T-shape toward the front. The narrower part21includes a nut groove21aextending in the radial direction and a pair of serrated joints21band21bexpanding to both sides.

Each T-nut31is slidably fitted in the associated nut groove21a. Each top jaw30is fastened to the associated T-nut31, with a serrated jointed part (not shown) of the top jaw30jointed to the associated joint21b. Accordingly, the top jaw30is integral with the master jaw20while being positioned with respect to the master jaw20.

The wider part22has a greater width than the narrower part21and has parts (corresponding to key protrusions) protruding beyond both sides of the narrower part21. The wider part22has, at the front on each lateral side of the narrower part21, a flat sliding surface (i.e., a narrower sliding surface22a) extending along the narrower part21. The narrower sliding surfaces22aand22aare ground to have high dimensional accuracy and smoothness.

In this master jaw20, the wider part22has, in the entire region radially outside the wedge23, a flat sliding surface (i.e., a wider sliding surface22b). The wider sliding surface22bis also finished, specifically ground, to have high dimensional accuracy and smoothness. The wider sliding surface22bis ground by sliding transversely (i.e., orthogonal to the sliding direction) unlike the known art.

Specifically, as shown inFIG. 9, a grinder of a grinding machine200is pressed onto the wider sliding surface22b, and is controlled to slide transversely as indicated by the white arrow D. The wider sliding surface22bis ground in this manner so as to have predetermined dimensional accuracy and smoothness. As a result, the wider sliding surface22bbecomes a smooth surface without any step and is slidable in both of the radial direction and the circumferential direction while being in surface contact.

The wedge23has a greater width than the narrower part21. In the case of this master jaw20, the wedge23has the same width as the wider part22, and the side end surface of the wedge23and the side end surface of the wider part22are continuous and flush with each other.

The wedge23includes a sliding part23aand a loosely fitting sliding part23b. The sliding part23ais fitted into the slid part41b(i.e. the radially inner part). The loosely fitting sliding part23bis fitted into the loosely fitted slid part41a(i.e., the radially outer part). The loosely fitting sliding part23bhas a smaller width than the loosely fitted slid part41a. The sliding part23ahas a smaller width than the slid part41b.

The sliding part23ahas, at both transverse ends, ground sliding surfaces24facing radially inward and outward. Accordingly, the sliding surfaces24and24come into surface contact with the slid surfaces42and slide along the associated wedge housing groove41.

Having the greater width, the wedge23has a sufficient strength even with a smaller thickness in the radial direction. Accordingly, the loosely fitting sliding part23bhas a wider end surface25extending from the edge of the wider sliding surface22band substantially orthogonal to the wider sliding surface22b. This wider end surface25is located inside the loosely fitted slid part41a. As a result, as shown inFIG. 7, while being fitted in the wedge housing groove41, the wedge23is housed inside the wedge housing groove41so as not to come out of the plunger40.

As shown inFIG. 11, each front slide13ahas the substantially same width as the associated narrower part21. On the other hand, each rear slide13bhas a slightly greater width than the associated wider part22. Both the side surfaces of the narrower part21come into surface contact with the inner surface (i.e., surfaces facing each other in the circumferential direction) of the front slide13aand slide. On the other hand, there is a gap S between each side surface of the wider part22and the surfaces of the rear slide13bfacing each other in the circumferential direction.

The thickness of the wider part22is substantially the same as the size of the rear slide13bin the axial direction. The surface (i.e., a wider slid surface14) corresponding to the bottom of each keyway13and facing the front of each rear slide13b, and the surface (i.e., a narrower slid surface15) protruding to each side of the front slide13aand facing the rear of the rear slide13bare both ground to be smooth surfaces. With this configuration, each master jaw20is fitted into the associated keyway13, which brings the narrower slid surfaces15into surface contact with the corresponding narrower sliding surfaces22a, and the wider slid surface14into surface contact with the wider sliding surface22b.

In conjunction with the slide of the plunger40in the axial direction, the master jaws20slide and shift in the radial direction. That is, once the plunger40slides forward, each master jaw20slides radially outward as indicated by the white arrow E inFIG. 12from the radially inner position as shown inFIG. 7. On the other hand, once the plunger40slides rearward, each master jaw20slides radially inward.

For example, in order to support the workpiece radially inside, the plunger40slides rearward from the state shown inFIG. 12and the master jaws20slide radially inward. In this manner, a workpiece is supported by the radially inner end surfaces of the top jaws30.

At this time, the radially inner end surfaces of the top jaws30receive a strong radially outward force, as in the known art shown inFIG. 1. In addition, the rears of the master jaws20receive a strong radially inward force from the plunger40via the contact regions between the slid surfaces42of the slid part41bof each wedge housing groove41and the sliding surfaces24of the sliding part23aof the wedge23. Accordingly, a strong moment (i.e., a torsional force) acts on the master jaws20which makes the master jaws20turn such that the radially outer sides head rearward and the radially inner sides head forward.

In the known art, as shown inFIGS. 3 and 4, the sliding surfaces are formed by grinding in the sliding direction. There are non-ground parts, having steps, at radially outside portions of each wedge106. The sliding surfaces are formed only on both sides of the non-ground parts. The torsional force is received via the sliding surfaces and the sliding surfaces facing forward.

The strong torsional effect is received via these regions having a small contact area. Thus, distortions or deformations tend to occur in the master jaws101b, which may result in floating of the top jaws30and give a negative influence on the support accuracy.

By contrast, in the chuck1, the sliding surfaces facing the rears of the master jaws20are formed by grinding in the direction orthogonal to the sliding direction. As a result, the wider sliding surfaces22bexpanding in the width direction are formed in the respective wider parts22of the master jaws20. As shown inFIG. 11, the entire regions of the wider sliding surfaces22bcome into surface contact with the wider slid surfaces14of the respective keyways13formed in the body10.

The surface contact used herein is complete surface contact with the entire regions of the wider sliding surfaces22bin one preferred embodiment, but may include non-contact parts such as grooves (or holes) for a grease supply passage, or clearance grooves (or holes) for facilitating the grinding processing. When supporting a workpiece, the master jaws20are inclined with respect to the associated keyways13due to the effects of the moments. Radially outer portions of the wider sliding surfaces22bcome into strong surface contact with the wider slid surfaces14. The regions corresponding to radially inner portions of the wider slid surfaces14could thus be not in contact with the wider slid surfaces14. Even in this case, larger areas of the master jaws20come into contact with the keyways13than in the known art.

Accordingly, the chuck1receives one of strong torsional forces acting on the master jaws20by the surface contact between the wider sliding surfaces22bhaving a large area and the wider slid surfaces14. As a result, distortions and deformations are less likely to occur in the master jaws20, and the floating of the top jaws30decreases, which improves the accuracy in supporting a workpiece. The workpiece can thus be stably supported.

In addition, the wider sliding surfaces22b, which is formed through grinding in the direction perpendicular to the sliding direction, eliminates the limits on the width of the wedges23to be smaller than the distance between the sliding surfaces on both sides. The wedges23have a greater width than the narrower parts21. Accordingly, the strength of the wedges23increases. There is thus no need to provide the ribs106asignificantly extruding in the radial direction to ensure the strength of the wedges23. The wedges23are housed in the plunger40.

As a result, there is no need to form any recess (see reference numeral107inFIGS. 1 and 5) in the body10not to come into contact with the ribs106a, whereby the rigidity of the body10improves.

In the known art, each wedge106has a narrow width as shown inFIG. 5, thereby easily causing distortions or deformations in the wedge106. By contrast, the chuck1includes the wider wedges23, which is less likely to cause distortions or deformations in the wedges23.

As in the known art, the narrower wedges concentrate the force acting on the body100from the plunger103in three portions of the body100in the circumferential direction as indicated by the white arrows inFIG. 5. Accordingly, larger distortions tend to occur in the body100.

By contrast, in the chuck1, the transverse ends of the sliding part23aof each master jaw20are dispersed in the circumferential direction. Specifically, as shown inFIGS. 13A and 13B, six portions of the respective transverse ends of the sliding part23aof each master jaw20(specifically, the radially inner or outer corners at the respective ends) are arranged in the circumferential direction at substantially equal intervals, that is, intervals at a central angle θ of about 60 degrees.

As indicated by the white arrows inFIG. 13B, the forces act on the body10from the plunger40. Since the outer circumferential surface of the plunger40is in surface contact with the inner peripheral surface of the housing chamber11, the forces act so as to push the body10outward as indicated by the white arrows.

The acting forces are distributed to six parts located at substantially equal intervals in the circumferential direction, which reduces distortions or deformations of the body10.

For example, it is confirmed from the calculation performed using simple models that if the magnitude of the force that acts is the same, the distortions of the body can be reduced to one tenth in a case in which the forces are distributed to six parts of the body located at equal intervals in the circumferential direction, compared with a case in which the forces are concentrated in three parts of the body located at equal intervals in the circumferential direction.

As described above, the chuck1disclosed in the embodiment is less likely to cause distortions or deformations in the body10or the master jaws20, thereby highly accurately and stably supporting a workpiece.

In the sliding portions, a sufficient lubricant needs to spread to smoothly operate the master jaws20or to reduce wears, for example. On the other hand, a grease is difficult to spread on the sliding portions if the slides have a larger area. This may cause disadvantages such as malfunctions or a decrease in durability.

To address the problem, the chuck1has a simple, devised structure for spreading the grease over the entire regions of the sliding portions including the sliding portions between the wider sliding surfaces22band the corresponding wider slid surfaces14.

As shown inFIGS. 7 and 9, for example, the chuck1has grease nipples50(example oil inlets) each on an end surface of each master jaw20facing outside in the radial direction and exposed to the outside of the chuck1. Although neither shown in the drawing nor described in detail, the grease is injected into each grease nipple50using a grease gun or any other devices, and each grease nipple includes an anti-backflow mechanism not to cause backflow of the injected grease.

The grease nipples50communicate with the housing chamber11via lubricant supply paths provided in the body10and the master jaws20. The lubricant supply paths are provided for the respective master jaws20and have the same structure. One of the lubricant supply paths will thus be described in detail.

The lubricant supply path includes an inlet hole51, a planar recess52, communication recesses53, vertical holes54, and linear recesses55, for example. A lubricant supply mechanism includes the grease nipple50and the lubricant supply path.

As shown inFIGS. 7 and 9, the inlet hole51is open in the master jaw20. The inlet hole51includes an upstream part51aand a downstream part51b. The upstream part51aextends radially inward from the grease nipple50to a substantial center of the master jaw20. The downstream part51bhas an opening at a substantial center of the wider sliding surface22band extends in the radial direction from the opening to be connected to the upstream part51a.

As shown inFIGS. 7, 8, 11, and 13B, the planar recess52is formed at the center of the wider slid surface14of the body10. The planar recess52is a shallow recess having a substantially rectangular shape in a top view and expands thinly along the wider slid surface14.

As shown inFIG. 11, the inlet hole51always communicates with the planar recess52in the range in which the master jaw20slides. The upper opening of the planar recess52is sealed by the wider sliding surface22band constitutes an intermediate part of the lubricant supply path.

As shown inFIGS. 13A and 13B, the planar recess52is located in a region overlapping the narrower part21(i.e., the front slide13a) as viewed in the axial direction. That is, as viewed in the axial direction, the recess is not formed in the region overlapping the narrower sliding surfaces22aon both sides of the master jaw20. The planar recess52in such a region can be easily formed through insertion of a general end mill into the front slide13aof the keyway13and cutting of the front slide13a.

As shown inFIGS. 9 and 10, the communication recesses53are open in the wider sliding surface22bof the master jaw20. The communication recesses53are circular recesses spaced apart from each other. As shown inFIG. 13A, when viewed in the axial direction, each communication recess53is provided in a region overlapping the narrower part21(i.e., the front slide13a) and the wider part22(i.e., the rear slide13b) including the boundary between these parts.

As shown inFIG. 11, a part of each communication recess53always communicates with the planar recess52.

As shown inFIGS. 9, 10 and 11, two vertical holes54are open in the master jaw20. Each vertical hole54penetrates the wider part22from an inlet54aopen at a portion toward the radially outer end of the narrower sliding surface22a, substantially orthogonally to the wider sliding surface22b. Each vertical hole54communicates with one of the communication recesses53.

Such configurations of the vertical holes54and the communication recesses53reduce a decrease in the area of the contact surface in a higher load region, thereby achieving stable support of the master jaw20.

As shown inFIGS. 10 and 13A, two linear recesses55are open in the master jaw20. Each linear recess55is a linear groove extending in the sliding direction at a transversely intermediate part of one of the narrower sliding surfaces22a. The radially outer end of each linear recess55is located in the surface of the narrower sliding surface22a(does not penetrate the narrower sliding surface22a) and communicates with one of the inlets54a.

On the other hand, the radially inner end of each linear recess55penetrates the narrower sliding surface22aand forms an outlet55acommunicating with the housing chamber11. As shown inFIG. 11, the upper opening of each linear recess55is sealed by one of the narrower slid surfaces15, thereby constituting a downstream part of the lubricant supply path.

Being injected from the grease nipple50, the grease passes through the inlet hole51and is introduced into the planar recess52. The grease introduced into the planar recess52spreads and fills the planar recess52. Once the planar recess52is filled with the grease, a further injected grease is introduced into the communication recesses53. Once the communication recesses53are filled with the grease, a further injected grease flows into the vertical holes54.

The grease that has flowed into the vertical holes54is introduced from the inlets54ainto the linear recesses55. A further injected grease fills each linear recess55and is introduced into the housing chamber11through the outlet55a. The outlet55ais the only outlet of each lubricant supply path. Thus, the grease injected in a sufficient amount fills the inlet hole51, the planar recess52, the communication recesses53, the vertical holes54, and the linear recesses55, and is supplied also to the housing chamber11.

Since the sliding portion between each wider sliding surface22band the corresponding wider slid surface14has the surface recess52and the communication recesses53, the grease spreads in a wide range in even a large area. Similarly, the sliding portion between each narrower sliding surface22aand the corresponding narrower slid surface15has the linear recess55. The grease can thus spread in a wide range even in an elongated sliding portion.

As shown inFIGS. 9 and 10, since each outlet55ais located at the end of the sliding part23aof the wedge23where the sliding surface24is formed, the grease spreads to the sliding portion between the sliding surface24and the slid surface42.

The sliding of the master jaws20in the radial direction causes the grease to spread more. The rotation of the chuck1generates a centrifugal force, which allows the grease that has flowed into the housing chamber11to flow along the surface of the wedge23and reach the radially outer side.

As a result, the grease stably spreads over the entire region of the sliding portions of the master jaws20.

The chuck according to the present invention is not limited to the embodiment described above and includes various other configurations.

For example, the number of the jaws is not limited to three, and may be two, or four or more. The planar recess52may be formed in the wider sliding surface22b. The linear recess55may be formed in the narrower slid surface15. The communication recess53may be formed in the wider slid surface14. In addition, the planar recess52, the linear recess55, and the communication recess53may be formed in both the wider sliding surfaces22band the wider slid surfaces14or both the narrower sliding surfaces22aand the narrower slid surfaces15.

The finishing processing is the grinding but is not limited thereto. For example, polishing or cutting may also be employed. Finishing processing allowing highly accurate processing may be employed in one preferred embodiment.

The shape of each communication recess53is not limited to the circle. For example, each communication recess53may be a pair of linear recesses (i.e., elongated grooves) extending in the circumferential or radial direction or intersecting each other (i.e., in an X shape), or may be a rectangular frame-like recess composed of continuous linear recesses extending in the circumferential and radial directions. While the chuck grasps the outside of a workpiece in the embodiment, the chuck may grasp the inside of a workpiece.

DESCRIPTION OF REFERENCE CHARACTERS