BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to collet chuck assemblies for holding a workpiece and more particularly to dead or true length collet chuck assemblies which hold the workpiece against axial displacement during the collet closing and opening sequences.

Background of the Invention True length collet chuck assemblies for holding a collet against longitudinal or axial displacement which would cause errors in the machining operation are well known.

For example, U. S. patents 5, 480,164 and 5,855,377, both of which are incorporated herein by reference, each discloses a dead length collet chuck assembly in which a standard collet is threadedly received by a collet retaining ring secured to an interior surface of a chuck body. A longitudinally displaceable camming or closing sleeve surrounding the collet and having a tapered, internal camming surface operatively associated with a conical, exterior surface on the split forward end portion of the collet, compresses and releases the jaws of the collet. The longitudinally displaceable closing sleeve is actuated by means of a mechanically or hydraulicjajly operated push tube mounted on the machine tool.

Although the true length collet chucks of the aforementioned patents substantial advanced the state of the art, there continues to exist a need for

still further improvements. For example, it would be desirable to provide a true length collet chuck that is not only compact but is self-contained, that is, not dependent on a push (or draw) tube or bar to actuate the collet jaws.

SUMMARY OF THE INVENTION In accordance with a specific, exemplary embodiment of the present invention, there is provided a true length collet chuck assembly for actuating a collet, wherein the collet comprises a rear portion and a compressible, split forward portion having a flared exterior surface, the split forward portion defining a plurality of jaws for holding a workpiece. The assembly comprises a chuck body carrying a collet retainer for engaging the rear portion of the collet so as to substantially fix the collet against axial movement relative to the chuck body. The chuck body further has a forward portion defining a bore centered on the longitudinal axis of the chuck body. A collet closing sleeve is slidably disposed within the bore of the chuck body and is axially displaceable relative to the collet. The closing sleeve includes a tapered interior surface in engagement with the flared exterior surface of the collet, whereby axial displacement of the closing sleeve relative to the collet causes actuation of the collet jaws to grip or release the workpiece. The collet closing sleeve further includes a threaded portion. A collet actuator having threads mating with the threaded portion of the closing sleeve, is rotatably carried by the chuck body.

Thus, rotation of the collet actuator causes axial displacement of the closing sleeve relative to the collet to actuate the jaws thereof.

In accordance with other aspects of the invention, the collet actuator comprises a ring-shaped element having an interior surface defining the threads mating with the threaded portion of the closing sleeve and a peripheral surface having gear teeth. The chuck body includes a side wall carrying a drive pinion meshing with the gear teeth on the collet actuator.

The drive pinion is rotated by means of a hand tool adapted to releasably

engage the drive pinion. Preferably, the drive pinion and the gear teeth on the collet actuator comprise a bevel gear drive, the drive pinion being rotatable about a radius of the chuck body.

The collet chuck assembly of the present invention is a compact, low profile manual unit that is self-contained, that is, the unit does not depend on a draw or push bar or tube incorporated in the machine tool for collet actuation. Thus, the collet chuck assembly of the invention is versatile in that it can be mounted in any position on a broad variety of machine tools including lathes, horizontal and vertical milling machines, grinders, and so forth.

BRIEF DESCRIPTION OF THE DRAWINGS Further features and advantages of the invention will become evident from the detailed description below when read in conjunction with the accompanying drawings in which: Fig. 1 is an axial cross section view of a collet chuck assembly in accordance with the present invention; and Fig. 2 is an axial, exploded cross section view of the assembly of Fig. 1 showing the main components of the assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes a preferred embodiment of the invention representing the best mode contemplated for practicing the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles of the invention whose scope is defined by the appended claims.

Referring now to the drawings, there is shown a collet chuck assembly 10 having a longitudinal, central axis 12. The chuck assembly 10 is attachable to the rotatable spindle (not shown) on a variety of machine tools,

including by way of example, lathes, horizontal and vertical milling machines, and grinders, by means of an appropriate adapter mounting plate, such as the adapter plate 14 to which the chuck assembly 10 is bolted.

The collet chuck assembly 10 includes a chuck body 16 having a main chuck body part 18 and a back plate 20. The main chuck body part 18 and the back plate 20 are bolted together by means of a number of screws (not shown) inserted into counterbored holes 21 from the rear face of the plate 20, thereby facilitating assembly and disassembly of the part 18 and plate 20. The chuck body 16 is bolted to the adapter plate 14 by screws 22, one of which is shown.

The chuck body 16 includes a generally cylindrical side wall 24 defined jointly by the chuck body part 18 and plate 20, and disposed concentric about the central longitudinal axis 12. The main chuck body part 18 has a front portion 26 defining a first bore 28 coaxial of the longitudinal rotational axis 12. The main chuck body part 18 further includes a rear portion 30 having a stepped second bore 32 concentric with and larger than the first bore 28. The second bore 32 terminates at a rearwardly facing radial wall 33. The back plate 20 includes a central bore 34 defined by an inner cylindrical wall 36. An annular flange 38 defining a series of longitudinally extending threaded holes 40 (one of which is shown) extends inwardly from the inner cylindrical wall 36 of the back plate 20.

Received within the bore 34 of the back plate 20 is a collet retaining ring 50 centered on the longitudinal axis 12 and having internal threads 52.

The collet retaining ring 50 includes an outwardly extending flange 54 having longitudinally extending throughholes 56 aligned with the threaded holes 40.

The collet retaining ring 50 is secured to the back plate 20 by bolts 58 passing through the 56 holes in the collet retaining ring flange 54 and extending into the threaded holes 40 in the flange 38. The collet retaining ring 50 further includes radially extending holes, such as the hole 60, intersecting the internal threads 52.

The chuck body main part 18 is adapted to receive a standard spring collet 70 having a split, flared front end 72 defining a plurality of jaws 74 for holding a workpiece. The collet 70 further includes a rear, threaded end 76 adapted to be received by the internal threads 52 on the collet retainer ring 50. The collet 70 is firmly secured to the collet retainer ring 50 by set screws 78 (one of which is shown) received by radially extending threaded holes 80 in the back plate 20 and tightened against the threads on the threaded end 76 of the collet so as to hold the collet in a fixed position relative to the chuck assembly 10.

A collet camming or closing sleeve 90 coaxial of the central axis 12 and disposed about the collet 70 is axially displaceable relative to the fixed collet within the first bore 28 to compress and release the jaws 74 of the collet. The closing sleeve 90 includes a front portion 92 and a rear portion 94. The front portion 92 has an internally flared surface 96 substantially matching the taper of the flared front end 72 of the collet. As is well known, the internally flared surface 96 engages the externally flared front end 72 of the collet to compress the jaws 74 to grip a workpiece when the closing sleeve 90 is axially displaced forwardly. Axial displacement of the sleeve rearwardly releases the jaws 74, allowing them to expand and release their grip on the workpiece.

The front portion 92 of the collet closing sleeve 90 has an outer cylindrical surface 98 that is axially slidable within the bore 28 of the main chuck body part 18. The sleeve 90 further has external threads 100 along the rear portion 94. A longitudinally extending slot 102 in the outer surface 98 of the closing sleeve 90 receives the inner end 104 of a radially disposed screw 106 received by a threaded hole 108 in the side wall 24 of the chuck body 16.

In this fashion, the closing sleeve 90 is freely movable in the axial direction but is restrained by the screw 106 against rotation relative to the chuck body.

The collet closing sleeve 90 is axially reciprocatable so as to compress or release the collet jaws 74, by means of an annular collet actuator 110 received

within the second bore 32 of the main chuck body part 18. The collet actuator 110 is rotatable about the axis 12 and includes internal threads 112 for receiving the external threads 100 on the closing sleeve 90. The collet actuator 110 further includes rear peripheral surface 114 defining a set of gear teeth 116. In this respect, the collet actuator 110 resembles a ring gear.

The collet actuator has front and rear, radially extending surfaces 118 and 119, respectively.

The chuck body 16 carries a drive pinion 120 journaled for rotation in a radially extending aperture 122 formed in the side wall 24 of the chuck body at the junction of the main chuck body part 18 and the back plate 20. The drive pinion 120 is thus rotatable about a radius of the chuck body. The drive pinion 120 has an inner end 124 provided with gear teeth 126 in mesh with the peripheral gear teeth 116 on the collet actuator 90, the drive pinion 120 and toothed collet actuator 90 thus forming a simple bevel gear transmission.

The outer end of the pinion 120 defines an axially extending keyed recess 128 having a square, hex or like cross section. A drive tool, such as a T-handle 130 having a correspondingly keyed end 132, is insertable in the pinion recess 128.

To minimize backlash, the annular collet actuator 110 is precisely positioned axially relative to the chuck body main part 18 and the backplate 20 by means of front and rear spacers 140 and 142, respectively. The front spacer 140, comprising an annular ring fabricated of high density polyethylene (HDP), is positioned between the front surface 118 of the collet actuator 110 and the wall 33 within the chuck body main part 18. The rear spacer, consisting of a pair of spaced apart washers 144 sandwiching a needle bearing 146, is disposed between the rear surface 119 of the collet actuator 110 and the front surface of the annular flange 38 on the backplate 20.

In operation, a collet 70 is inserted into the closing sleeve 90 and is rotated clockwise to engage the collet retaining ring threads 52, until the collet stops. With the collet installed and a workpiece in the collet, the

workpiece is clamped by inserting the"T"handle end 132 into the recess 128 in the pinion 120 and rotating the T-handle in a clockwise direction. As the pinion 120 is thus turned, the pinion rotates the collet actuator 110 with which the pinion meshes. As a result, the closing sleeve 90 (whose rear portion threadedly engages the collet actuator 110, using left hand threads) is forced to move axially in a forward direction, causing the taper in sleeve 90 to engage the matching taper on the collet, forcing the collet jaws 74 to contract, thereby gripping the workpiece. The more force that is applied to the"T" handle, the more grip force is applied to the workpiece. It will thus be seen that the bevel gear transmission comprising the drive pinion 120 and the collet actuator 110 driven thereby, converts the rotation of the T-handle 130 about a radius of the chuck body to rotation of the collet actuator 110 about the central chuck body axis 12. Since the collet 70 is retained in a fixed axial position by the collet retaining ring 50, linear displacement of the workpiece is minimized, allowing close tolerance linear lengths to be maintained.

While the present invention has been described with reference to particular illustrative embodiments, the invention is not intended to be restricted to those embodiments but only by the appended claims. It will be appreciated that those skilled in the art can change or modify the described embodiments, or substitute equivalents for the various elements described and shown, without departing from the scope and spirit of the invention. For example, a worm gear transmission could be substituted for the bevel gear drive transmission described above. In such a case, the drive worm would be substituted for the pinion 120 and adapted to be rotated by the T-handle 130.

Similarly, the worm gear, driven by the worm, would be substituted for the above-described ring gear on the collet actuator 110.