Tool holder

In order to provide a tool holder which greatly reduces frictional resistance between a locknut and a taper collet, and eliminates a twisting of the taper collet during tightening of the locknut, in a tool holder comprising a locknut 13 which pushes a taper collet 12 into a tapered hole 115 of a collet chuck body 11 to chuck a cutting tool 15, between a reference end 123 of the tape collet 12 and a collet supporting portion 131 opposed thereto, interposed is a bearing washer 14 to reduce frictional resistance between both contact surfaces. To both surfaces of this bearing washer 14, namely, to the respective surfaces which come into contact with the reference end 123 and collet supporting portion 131, surface treatment by any of ion nitriding, DLC (Diamond-Like Carbon) coating, and TiN coating is applied.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tool holder which grasps and holds a cutting tool such as a drill in a collet chuck by a slotted taper collet and a locknut, and more particularly, it relates to a tool holder in which a contact part between a locknut and a taper collet is coupled via a bearing washer.

2. Description of the Prior Art

In terms of a conventional tool holder of this type, in order to grasp and hold a cutting tool such as a drill in a collet chuck body by a slotted taper collet and a locknut, a coupling groove is formed in a ring shape around the entire outer circumference of a cutting tool inserting-side end portion of the taper collet, a convex thread portion to be engaged with the coupling groove is provided in a ring shape on the inner circumference of the locknut, and this convex thread portion is engaged with the coupling groove, whereby the taper collet is coupled to the locknut so as to be relatively rotatable.

Next, the taper collet in a coupled condition is inserted into a tapered hole provided on the inner circumference of the front-end portion of the collet chuck body and the locknut is screwed with a male screw portion provided on the outer circumference of the front-end portion of the collet chuck, whereby the taper collet is temporarily attached by insertion in the collet chuck body. Then, by tightening the locknut after inserting a shank portion of the cutting tool into a tool insertion hole, the taper collet is pushed into the tapered hole of the collet chuck body and is reduced in its diameter, whereby the cutting tool is held in the collet chuck body (See Non-patent literature 1, for example).

However, in such a conventional tool holder as described above, since the convex thread portion of the locknut is directly engaged with the coupling groove of the taper collet, when the tapered portion of the taper collet is pushed into the tapered hole of the collet chuck body by screwing the locknut with the male screw portion of the collet chuck body and tightening the same, press force to the tapered collet is biased due to surface roughness and friction, etc., between the contact surfaces of the mutually engaged ring-like coupling groove and ring-like convex thread portion, and moreover, torsional force due to a rotation of the locknut is transmitted to the taper collet. Due to this biased press force, the tapered portion of the taper collet may be pushed into the tapered hole of the collet chuck body in an inclining manner, and this phenomenon becomes noticeable as the collet becomes smaller in size.

In addition, if the taper collet is chucked in the collet chuck body in an inclined manner, a rotation run-out occurs at the cutting tool grasped and held in the taper collet, therein exists a problem such that a harmful influence is exerted to the workpiece cutting work.

In addition, as a result of the torsional force transmission to the taper collet, the taper collet grabs and supports the cutting tool in a twisted condition, therein exists a problem such that chucking of the cutting tool is hindered.

SUMMARY OF THE INVENTION

The present invention has been made for solving such problems as described above, and it is an object of the present invention to provide a tool holder which greatly reduces frictional resistance between a locknut and a taper collet, unifies press force to the taper collet by tightening of the locknut, and eliminates a twisting of the taper collet during tightening of the locknut.

In order to achieve the above object, according to the first aspect of the present invention, a tool holder comprises: a collet chuck body; a slotted taper collet to be fitted in a tapered hole formed in the front-end portion of the collet chunk body; a locknut which is screwed with a male screw portion formed on the outer circumference of the front-end portion of the collet chuck body and which holds cutting tool by inserting the taper collet into the tapered hole, wherein the taper collet has, at the front end of the cutting tool inserting side thereof, a reference end perpendicular to the axis line of the taper collet and a cylindrical nut engaging portion protruded from the reference end with its axis line aligned, the locknut has a collet supporting portion formed in a manner protruded in the center direction of the locknut so as to be opposed to the reference end and an insertion hole concentrically formed in the center of the collet supporting portion so as to allow an insertion of the nut engaging portion, the taper collet has a brim portion which is formed on the outer circumference of the front end of the nut engaging portion inserted through the insertion hole and which couples, by latching with the marginal rim of the insertion hole, the taper collet to the locknut so as to be relatively rotatable, a metal ring plate-like bearing washer is interposed between the reference end and the collet supporting portion opposed thereto, and to at least one surface of the bearing washer which comes into contact with the reference end and the collet supporting portion, surface treatment to reduce frictional resistance between both contact surfaces is applied.

As has been described in the above, according to the tool holder of the present invention, since a bearing washer which has received surface treatment by any of ion nitriding, DLC coating, TiN coating, and mirror-surface lapping is interposed between the reference end on the cutting tool inserting side of the taper collet and collet supporting portion of the locknut, frictional resistance between the mutual contact surfaces can be greatly reduced. Consequently, the press force into the taper collet by tightening of the locknut can be unified, and the taper collet can be securely pushed without inclination into the tapered hole in a manner following a taper of the tapered hole. Thereby, effects are provided such that, a tool can be held in the collet chuck body without inclining the taper collet, rotation run-out of the cutting tool grasped and held by the taper collet can be eliminated, and the tool holder becomes preferable as a tool holder using a small-sized collet.

In addition, according to the tool holder of the present invention, since a bearing washer which has received surface treatment by any of ion nitriding, DLC coating, TiN coating, and mirror-surface lapping is interposed between the reference end of the taper collet and collet supporting portion of the locknut, twisting of the taper collet during tightening of the locknut is eliminated, whereby the run-out accuracy of the taper collet can further be improved.

In addition, according to another aspect of the present invention, the bearing washer inserted in the ring-like supporting groove is held in the locknut by a snap ring disengageably attached by insertion in the engaging groove, therefore, an attachment of the bearing washer to the inside of the locknut and a detachment of the bearing washer from the locknut can be easily carried out.

In addition, according to yet another aspect of the present invention, since the surface of the collet supporting portion of the locknut with which the bearing washer comes in contact is formed in an arc surface protruded in an convex shape, the contact area between the bearing washer and collet supporting portion is reduced, whereby the frictional resistance between the bearing washer and collet supporting portion can further be reduced.

In addition, according to another aspect of the present invention, since the bearing washer can be held in the locknut by disengageably engaging the plurality of projections provided in a protruded manner on the margin of the bearing washer with the holding groove, an attachment of the locknut to the inside of the locknut and a detachment of the bearing washer from the locknut can be easily carried out.

In addition, according to yet another aspect of the present invention, since the bearing washer can be held in the locknut by disengageably engaging the marginal portion of the bearing washer with the plurality of holding projections formed with a ring-like layout on the inner circumferential surface of the locknut, an attachment of the bearing washer to the inside of the locknut and a detachment of the bearing washer from the locknut can be easily carried out.

In addition, according to still yet another aspect of the present invention, since the slot for a diameter reduction is formed in the radial direction in the bearing washer, the bearing washer can be easily attached to the locknut.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a longitudinal sectional view showing an assembled condition of a tool holder according to a first embodiment of the present invention,FIG. 2Ais a sectional view showing the tool holder according to the first embodiment of the present invention in an exploded manner, andFIG. 2Bis an enlarged sectional view of a bearing washer.

In FIG.1andFIG. 2A, a tool holder10comprises a collet chuck body11whose central axis part is hollow, a taper collet12with slots121to enable a diameter reduction, a locknut13to hold a cutting tool15such as a drill via the taper collet12, and a metal bearing washer14.

The collet chuck body11is to be attached by insertion in a main spindle of a machine tool (unillustrated), and this collet chuck body11has, as shown in FIG.1andFIG. 2A, a taper shank portion111whose diameter is gradually reduced from the front-end side to the rear end; a grasping and holding flange portion112formed at a large-diametrical end portion of the taper shank portion111; and a cylindrical cutting tool attaching portion113extended from the end face of a counter-taper shank portion side of the flange112in the direction opposite to the taper shank portion112with its axis line aligned, and a tapered hole114whose diameter is gradually reduced from the front end to the rear end is formed at a forward part of the inner circumference of the cutting tool attaching portion113. In addition, a male screw portion115with which a locknut13is to be screwed is formed on the outer circumferential surface of the cutting tool attaching portion113.

The taper collet12is for attaching the cutting tool15to the collet chuck11by closely fitting the same in the tapered hole114of the collet chuck11, and this taper collet12has, as shown in FIG.1andFIG. 2A, a tapered portion122which is fitted in the tapered hole114of the collet chuck body11and whose diameter is gradually reduced from the front end to the rear end; at the front end of the cutting tool15inserting side of the large-diametrical end face of the tapered portion122, a reference end123which is perpendicular to the axis line of the taper collet12; and a cylindrical nut engaging portion124protruded from this reference end123with its axis line aligned.

This taper collet12is designed to grasp and hold a cutting tool when the taper collet12is pushed into the tapered hole114by screwing and tightening the locknut13with the male screw portion115formed on the outer circumference of the front-end portion of the cutting tool attaching portion113.

The locknut13has, as shown in FIG.1andFIG. 2A, a collet supporting portion131formed such that it protrudes in the center direction of the locknut13so as to be opposed against the reference end123of the taper collet12; and an insertion hole132is concentrically formed at the center of the collet supporting portion131so as to allow an insertion of the nut engaging portion124.

In addition, the taper collet12has a brim portion125which is formed on the outer circumference of the front end of the nut engaging portion124inserted through the insertion hole132and which couples, by being latched with the marginal rim of the insertion hole132, the taper collet12to the locknut13so as to be relatively rotatable.

The bearing washer14is interposed between the reference end123and the collet supporting portion131opposed thereto for reducing frictional resistance between both contact surfaces and defines a ring plate having an outside diameter corresponding to the inner circumferential diameter of the locknut13, and both surfaces14aand14b(seeFIG. 2b) of this bearing washer14, namely, the respective surfaces which come in contact with the reference end123and the collet supporting portion131are provided with low-friction processed layers141and142by any of ion nitriding, DLC (Diamond-Like Carbon) coating, TiN coating process, and mirror-surface lapping.

In addition, such a bearing washer14is detachably supported in the locknut13by a holding means16.

The holding means16has, as shown in FIG.1andFIG. 2A, a ring-like holding groove161formed on the inner circumferential surface of the locknut13so as to hold the bearing washer14in contact with the collet supporting portion131, and this holding groove161is constructed by a convex thread portion162formed in a ring shape, on the inner circumferential surface of the locknut13, at an appointed distance corresponding to the thickness of the bearing washer14from the collet supporting portion131, and a counter-collet supporting portion side surface162aof this convex thread portion162is inclined so that the thickness of the convex thread portion162is gradually reduced from the inner circumferential surface of the locknut13toward the center direction.

The reason that the inclined surface162ais provided in the convex thread portion162is to ease insertion into the holding groove161when the outer circumferential rim of the bearing washer14is engaged with the holding groove161of the locknut13.

In terms of the tool holder10constructed as above, for chucking the cutting tool15in the collet chuck body11, by, first, inserting one end portion of the bearing washer14in the holding groove161of the locknut13from the convex thread portion162side, then pushing the other end portion of the bearing washer14against the inclined surface of the convex thread portion162and inserting the same in the holding groove161, the bearing washer14is fitted to the locknut13. Then, the taper collet12is, from its nut latching portion124side, inserted into the locknut13, and the brim portion125including the nut latching portion124is, with a reduced diameter, inserted through the insertion hole132of the locknut13. Thereafter, by restoring the brim portion125including the nut latching portion124to its original state, the taper collet12is connected to the locknut13so as to be relatively rotatable.

Then, after inserting the tapered portion122of the taper collet12into the tapered hole114of the collet chuck body11, the taper collet12is temporarily tightened to the collet chuck11by screwing a female screw portion133of the locknut13with the male screw portion115of the collet chuck body11. Then, after inserting a shank portion151of the cutting tool15into a tool insertion hole126of the taper collet12, the locknut13is completely tightened. Thereby, the tapered portion122of the taper collet12is pushed into the tapered hole114of the collet chuck body11and is reduced in diameter, and thereby holds the cutting tool15in the collet chuck body11.

At this time, as shown inFIG. 1, the bearing washer14is interposed between the reference end123of the taper collet12and the collet supporting portion131of the locknut13, and moreover, on both surfaces14aand14bof the bearing washer14which come in contact with the reference end123and the collet supporting portion131, formed are the low-friction processed layers141and142, which have received surface treatment to reduce frictional resistance by any of ion nitriding, DLC (Diamond-Like Carbon) coating, and TiN coating, and therefore, the frictional resistance between the contact surfaces can be greatly reduced. Accordingly, the press force to the taper collet12by tightening the locknut13becomes uniform, and no torsional force due to a rotation is transmitted to the taper collet12. Consequently, the tapered portion122of the taper collet12can be securely inserted into the tapered hole114without inclination, in a manner following a taper of the tapered hole114, and moreover, a twisting of the taper collet during tightening of the locknut is eliminated.

Accordingly, in the tool holder according to the first embodiment, a cutting tool can be held in the collet chuck body11without inclining the taper collet12, and rotation run-out of the cutting tool15grasped and held by the taper collet12can be eliminated, and the tool holder can be preferably used as2a tool holder using a small-sized collet, and therefore, the problem of deterioration of the cutting accuracy of the workpiece is addressed.

In addition, in the tool holder according to the first embodiment, since the bearing washer14is interposed between the reference end123of the taper collet12and the collet supporting portion131of the locknut13, twisting of the taper collet12during tightening of the locknut13is eliminated, whereby run-out accuracy of the taper collet12can further be improved.

Next, a second embodiment of a bearing washer holding means in a tool holder of the present invention will be described with reference to FIG.3.

FIG. 3is a longitudinal side view of a locknut and a bearing washer holding mechanism portion showing the second embodiment of a bearing washer holding means in a tool holder of the present invention.

In thisFIG. 3, identical reference numerals are used for components identical to those ofFIG. 1,FIG. 2A, andFIG. 2B, description of the construction thereof is omitted, while differences fromFIG. 1,FIG. 2A, andFIG. 2Bwill be selectively described.

In this embodiment, a difference fromFIG. 1,FIG. 2A, andFIG. 2Bexists in the holding means17of the bearing washer14.

The holding means17comprises a ring-like holding groove171formed on the inner circumferential surface of a locknut13so as to hold a bearing washer14in contact with a collet supporting portion131of the locknut13, a ring-like engaging groove172formed on the inner circumference of the locknut13, adjacent to the holding groove171, and a snap ring173which is disengageably attached by insertion in the latching groove and which holds the bearing washer14in the holding groove171.

In this second embodiment, since the bearing washer14inserted in the ring-like holding groove171is held in the locknut13by the snap ring173which is disengageably attached by insertion in the engaging groove172, an attachment of the bearing washer14to the inside of the locknut13and a detachment of the bearing washer14from the locknut13can be easily carried out.

Now, a modification of a locknut in a tool holder of the present invention will be described with reference to FIG.4.

FIG. 4is a longitudinal section view showing a modification of a locknut in a tool holder according to the present invention.

In thisFIG. 4, identical symbols are used for components identical to those ofFIG. 1,FIG. 2A, andFIG. 2B, description of the construction thereof is omitted, while differences fromFIG. 1,FIG. 2A, andFIG. 2Bwill be selectively described.

In the locknut13shown in this embodiment, a difference fromFIG. 1,FIG. 2A, andFIG. 2Bexists in that a surface131aof a collet supporting portion131of a locknut13with which a bearing washer14comes into contact is formed on an arc surface131bwhich is protruded in a convex shape toward the convex thread portion162.

According to such an embodiment, since the surface131aof the collet supporting portion131of the locknut13with which the bearing washer14comes into contact is formed on the arc surface131bwhich is protruded in a convex shape toward the convex thread portion162, a contact area between the bearing washer14and collet supporting portion131is reduced, whereby the frictional resistance between the bearing washer14and collet supporting portion131can further be reduced.

Now, still another embodiment of a bearing washer holding means in the tool holder of the present invention will be described based on FIG.5and FIG.6.

FIG. 5is a longitudinal side view of a locknut and a bearing washer holding mechanism portion showing a third embodiment of a bearing washer holding means in a tool holder of the present invention.

FIG. 6is a plan view of a bearing washer according to the third embodiment of the present invention.

In FIG.5andFIG. 6, identical symbols are used for components identical to those ofFIG. 1,FIG. 2A, andFIG. 2B, description of the construction thereof is omitted, while differences fromFIG. 1,FIG. 2A, andFIG. 2Bwill be selectively described.

In this embodiment, a difference fromFIG. 1,FIG. 2A, andFIG. 2Bexists in the holding means18of the bearing washer14.

The holding means18comprises a ring-like holding groove181formed on the inner circumferential surface of a locknut13so as to hold a bearing washer14in contact with a collet holding portion131of a locknut13, and, at two marginal parts of the bearing washer separated by 180 degrees in the circumferential direction, a plurality of protrusions182are formed across an angle of approximately 90 degrees so as to protrude outward from the margin of the bearing washer14and are disengageably engaged with the holding groove181.

Then, the outside diameter of the bearing washer14excluding the protrusions182is equivalent to the inside diameter of a convex thread portion181aof the holding groove181. In addition, the counter-collet supporting portion side surface of the convex thread portion181ahas an inclined shape so that the thickness of the convex thread portion181ais gradually thinned from the inner circumferential surface of the locknut13toward the center direction.

In the third embodiment having such a holding means18, by disengageably engaging the plurality of protrusions182that is provided in a protruded manner from the margin of the bearing washer14with the holding groove181, the bearing washer14can be held in the locknut13, therefore, an attachment of the bearing washer14to the inside of the locknut13and a detachment of the bearing washer14from the locknut13can be easily carried out.

Now, a fourth embodiment of a holding means for a bearing washer in a tool holder of the present invention will be described based on FIG.7and FIG.8.

FIG. 7is a longitudinal side view of a locknut and a bearing washer holding mechanism portion showing the fourth embodiment of a bearing washer holding means in a tool holder of the present invention, andFIG. 8is a transverse plan view along the8—8line of FIG.7.

In FIG.7andFIG. 8, identical symbols are used for components identical to those ofFIG. 1,FIG. 2A, andFIG. 2B, description of the construction thereof is omitted, while differences fromFIG. 1,FIG. 2A, andFIG. 2Bwill be selectively described.

In the fourth embodiment, a difference fromFIG. 1,FIG. 2A, andFIG. 2Bexists in the holding means19of the bearing washer14.

In order to hold the bearing washer14in contact with the collet supporting portion131of the locknut13, the holding means19has, at two parts of the inner circumferential surface separated by 180 degrees in the inner circumferential direction of the locknut13, a plurality of holding protrusions191formed with a ring-like layout so as to protrude from the inner circumferential surface toward the center direction, and by engaging the outer circumferential rim of the bearing washer14with these holding protrusions191, the bearing washer14is detachably held in the locknut13.

A counter-collet supporting portion-side surface191aof the holding protrusions191has an inclined shape so that the thickness of the holding protrusions191is gradually thinned from the inner circumferential surface of the locknut13toward the center direction.

In the fourth embodiment having such a holding means19, by disengageably engaging the marginal portion of the bearing washer14with the plurality of holding protrusions191formed with a ring-like layout on the inner circumferential surface of the locknut13, the bearing washer14can be held in the locknut13, therefore, an attachment of the bearing washer to the inside of the locknut13and a detachment of the bearing washer14from the locknut13can be easily carried out.

Now, another embodiment of a bearing washer in a tool holder of the present invention will be described based on FIG.9.

FIG. 9is a plan view showing another embodiment of a bearing washer in a tool holder of the present invention.

In thisFIG. 9, a difference from the above embodiment exists in that a slot143for a diameter reduction is formed in the radial direction in a bearing washer14.

According to such an embodiment, since the slit143is formed in the bearing washer14, by pressing the whole bearing washer14against the inclined surface of the convex thread portion162after placing the bearing washer14on the inclined surface of the convex protruded portion162in the locknut13, the bearing washer14can be easily fitted to the holding groove161of the locknut13while the diameter is reduced.

In the above embodiment, a description has been given in a case where surface treatment for a frictional resistance reduction is applied to both surfaces of the bearing washer14which comes in contact with the reference end123of the taper collet12and collet supporting portion131of the lock nut13, however, the present invention is not limited hereto and surface treatment for a frictional resistance reduction may be applied at least to the surface of the bearing washer14which comes in contact with the collet supporting portion131of the locknut13.