Abstract:
A collet chuck assembly for an axially fixed collet head. The collet head is fixedly and removably mounted in a threaded bushing to prevent axial motion, and is keyed into place to prevent rotation. A sleeve assembly has cam surfaces adapted to engage the cam surfaces of the collet head to open and close the collet head, and slides between collet head open and collet head closed positions within a spindle adapter body. The sleeve assembly has projections that extend from a rearward portion and pass through appropriately sized passages in the axially-fixed bushing. Motion from a spindle drawbar is transmitted by a drawbar link-up through the projections of the sleeve assembly. Using this arrangement, no physical connection is required between the drawbar link-up and the sleeve assembly. Additionally, no cap assembly is required.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to collet chucks for holding a tool or workpiece on a spindle of a turning machine. 
     2. Description of Related Art 
     Collet chucks are used to clamp or grip workpieces or tools in turning machines, such as lathes. The collet head inside the chuck includes a number of circumferentially-spaced gripping segments and a number of cam surfaces. When the collet head is moved axially, its cam surfaces interact with corresponding opposing surfaces or cams on the mounting fixture. The interaction of the opposing cam surfaces causes the gripping segments of the collet head to expand or contract, thus causing it to grip or release a workpiece or tool, depending on the direction of axial movement. 
     Collet chucks are commonly used in place of other types of chucks, especially for smaller workpieces, because they are typically more accurate and can transmit more torque than a conventional chuck, such as a jaw chuck. Another advantage of collet chucks is that they maintain their grip at high rotational speeds, whereas the centrifugal forces present at high rotational speeds may cause a conventional jaw chuck to loosen its grip on the workpiece. 
     In conventional collet chucks, the axial movement required to grip the workpiece also moves the workpiece. This can be undesirable, because variations in diameter from workpiece to workpiece may result in variations in workpiece position, since the position at which the workpiece is grasped depends on the difference in diameter between the open collet head and the workpiece. 
     DEAD-LENGTH™ collet chucks are often used to eliminate the inconvenience associated with collet head axial movement. In such chucks, the collet head is held in an axially fixed position while a selectively axially moveable collet closing sleeve is moved. The collet closing sleeve has cam surfaces which engage those of the collet head, forcing the collet head to open or close, depending on the collet closing sleeve&#39;s direction of movement. Typically, collet closing sleeves are moved forward to close the collet head and rearward to open it. 
     In most DEAD-LENGTH™ collet chucks, the collet head gripping segments are held in an axially fixed position by a cap which is bolted or otherwise secured to the forward end of the collet closing sleeve. The collet head segments bear against the cap, and since they cannot move forward because of the cap, they are forced to either open or close in response to movement of the collet closing sleeve. When the collet head needs to be changed, for example, to replace the seals between segments, the cap must be removed. Although some caps are designed for quick removal and replacement, the cap is an intricate part and its removal may be an inconvenience to the user. 
     DEAD-LENGTH™ collet head is typically mounted on the spindle of a user&#39;s turning machine and is connected to the draw bar of the machine. The link-up components that connect the collet closing sleeve to the user&#39;s spindle and draw bar may need to be specially fabricated for each user&#39;s machine. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention relates to a collet chuck assembly with an axially fixed collet head. The collet chuck assembly comprises a spindle adapter body, a sleeve assembly, one or more resilient elastic members and a bushing member. 
     The sleeve assembly of the collet chuck assembly has outer surfaces constructed and adapted to slidingly engage corresponding inner surfaces of the spindle adapter body. This sliding engagement facilitates axial movement along a collet assembly movement axis. The sleeve assembly defines an interior collet head receiving passage which has engaging, motion-translating surfaces on at least a portion. The sleeve assembly also comprises a rear portion having one or more bearing surfaces extending perpendicularly with respect to the collet assembly movement axis. A set of projections extend from the rear portion substantially parallel to the collet assembly movement axis. Resilient elastic members are installed between the bearing surfaces of the sleeve assembly and corresponding bearing surfaces of the spindle adapter body. A bushing member is constructed and arranged to be removably and fixedly mounted within the interior cavity of the spindle adapter body proximate to the sleeve assembly. The bushing member has a central passage positioned and adapted to be operationally contiguous with the collet head receiving passage of the sleeve assembly. The central passage has structure constructed and arranged to secure a collet head against movement along the collet assembly movement axis. The bushing member also defines one or more passages arranged to receive the projections of the sleeve assembly so as to place the sleeve assembly in motion-transmitting relation with motion-generating or transmitting structures connected to the turning machine. 
     Another aspect of the invention relates to a turning machine. The turning machine comprises a spindle, a drawbar, and the collet chuck assembly described above. 
     A further aspect of the invention relates to an actuation mechanism for a collet head. The actuation mechanism comprises a sleeve assembly adapted to move between first and second positions along a first movement axis, the first position establishing an open position of the collet head and the second position establishing a closed position of the collet head. The sleeve assembly has engaging, motion-translating surfaces constructed and arranged to engage corresponding surfaces of the collet head. The sleeve assembly also has projections constructed and arranged to be inserted through a fixed member so as to transmit motion to the sleeve assembly. Additionally, the actuation mechanism comprises one or more resilient elastic members that are adapted to bear against an outer surface of the sleeve assembly and a bearing surface of another structure while resiliently resisting movements of the sleeve assembly between the first and second positions. 
     These and other aspects of the invention will be described below in greater detail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described with reference to the following Drawings, in which like reference numerals represent like features throughout the several views, and in which: 
     FIG. 1 is an axial cross-sectional view of a collet chuck assembly according to the present invention with the collet head in the closed position; 
     FIG. 2 is an exploded cross-sectional view of the collet chuck assembly of FIG. 1; 
     FIG. 3 is an axial cross-sectional view of the collet chuck assembly similar to the view of FIG. 1 with the collet head in the open position; 
     FIG. 4 is an elevational view of a sleeve-and-pin assembly of the collet chuck assembly; and 
     FIG. 5 is a plan view of a threaded bushing according to the invention. 
    
    
     DETAILED DESCRIPTION 
     A collet assembly with an axially fixed collet head, generally indicated at  10 , is shown in the axial cross-sectional view of FIG.  1 . In the view of FIG. 1, the collet assembly  10  is installed on the spindle  12  of a turning machine. The collet assembly  10  itself comprises a spindle adapter body  14 , a sleeve-and-pin assembly  16 , a threaded bushing  18 , a drawbar link-up  20 , and a collet head  22 . These components, their functions, and the operation of the collet assembly  10  will be described below. 
     In the description that follows, certain directional terms, such as “rear,” “forward,” “top,” “bottom,” “horizontal,” and “longitudinal” will be used. These terms refer only to the coordinate system of the Figures, and are used to simplify the description. Where these terms are used to describe a force, direction, or other quantity, only one component of the force, direction or other quantity need be in the indicated direction, unless otherwise stated. Additionally, the term “axially,” as used in the following description, is used with respect to the horizontal axis A shown in FIG.  1 . 
     An exploded view of the collet assembly  10  components is shown in FIG.  2 . As shown in FIGS. 1 and 2, a rearward end  24  of the spindle adapter body  14  is adapted to be bolted or otherwise connected to the spindle  12 . The spindle adapter body  14  has an interior cavity  26  formed axially through its length. The interior cavity  26  of the spindle adapter body  14  is dimensioned appropriately to receive the other components of the collet assembly  10 . 
     The rearward end  24  of the spindle adapter body  14  receives the drawbar link-up  20 . A keyscrew  28  extends through a radial hole  30  provided in the spindle adapter body  14  to key the drawbar link-up  20  to the spindle adapter body  14 , however, the connection between the spindle adapter body  14  and the drawbar link-up  20  is such that the drawbar link-up  20  may move axially within the interior cavity  26  of the spindle adapter body  14 . 
     Those of ordinary skill in the art will realize that the drawbar link-up  20  is a component of the turning machine itself, not a component of the collet assembly  10 . Although one possible exemplary configuration of the drawbar link-up  20  is illustrated in the Figures, the configuration will vary, and may take many forms. In general, the collet assembly  10  may be adapted to function with a drawbar link-up  20  of any configuration. 
     FIG. 5 is a plan view of the threaded bushing  18 . As shown in FIG. 5, the threaded bushing  18  is an annular component that mates with the spindle adapter body  14  just forward of the drawbar link-up  20 . More particularly, the threaded bushing  18  has threads  19  on its outer diameter which are adapted to threadedly engage corresponding screw threads provided on wall portions of the interior cavity  26 . The threaded bushing  18  also includes threads  21  on its inner diameter which are sized and adapted to threadedly engage and secure the rearward portion of the collet head  22  by means of corresponding threads that are provided on the rearward outer diameter of the collet head. The engagement of the threads  21  on the threaded bushing  18  with the threads of the collet head  22  prevents the collet head  22  from moving axially. (The threads  19 ,  21  of the threaded bushing  18  are most clearly seen in FIG. 2.) 
     Additionally, in order to prevent rotational movement of the collet head  22  from loosening the collet head  22  in the threaded bushing  18 , the collet head  22  is typically keyed. In order to engage the key on the collet head  22  and thus prevent the collet head  22  from rotating, the spindle adapter body  14  defines four circumferentially-spaced threaded through-holes  34  that extend through the spindle adapter body  14 . Four corresponding circumferentially-spaced threaded radial holes  33  are provided in the threaded bushing  18 . The holes  33  of the threaded bushing  18  are positioned so as to be contiguous with those of the spindle adapter body  14  when the threaded bushing  18  is installed in the spindle adapter body  14 . When the collet head  22  is inserted into the collet chuck assembly  10 , its keyway is rotated until it coincides with one of the sets of through-holes  34 , 33  and a keyscrew  32  is inserted into that set of through-holes  34 , 33 , thus preventing the collet head  22  from moving axially. The other three sets of through-holes  34 , 33  (i.e., those through-holes that do not correspond to the position of the collet head key) would then be filled with machine screws, which would prevent debris from entering the spindle adapter body  14  and would also help to secure the threaded bushing  18  in place. 
     The threaded bushing  18  acts as an interface between the drawbar link-up  20  and the sleeve-and-pin assembly  16  by means of a number of through-holes  36  extending axially through the thickness of the threaded bushing  18 . Pins  38  are fixed at one end in the sleeve-and-pin assembly  16  and extend rearwardly from the sleeve-and-pin assembly  16 . The pins  38  may be fixed to the sleeve-and-pin assembly  16  in any number of ways, for example, by way of a threaded connection between the two, or, in some cases, by means of an adhesive. One way to secure the two components is to provide corresponding threads on the pins  38  and sleeve  16  and then secure the pins  38  in place with a small amount of an adhesive, such as a cyanoacrylate adhesive. The pins  38  and sleeve  16  may also be integrally formed. 
     The through-holes  36  of the threaded bushing  18  and pins  38  of the sleeve-and-pin assembly  16  are located in corresponding positions with respect to one another, such that when the sleeve-and-pin assembly  16  is operatively positioned just forward of the threaded bushing  18  (as shown in FIG.  1 ), the pins  38  extend rearwardly through the through-holes  36  of the threaded bushing  18 . In this way, when the drawbar link-up  20  moves axially forward and contacts the pins, the sleeve-and-pin assembly  16  moves axially forward as well. 
     The sleeve-and-pin assembly  16  is shown in more detail in FIG. 4, a side elevational view. The sleeve-and-pin assembly  16  is hollow and generally tubular in shape and has outer surfaces As shown, it has a flanged rear portion  40  from which the pins  38  protrude rearwardly. The sleeve-and-pin assembly  16  has a total of four circumferentially-spaced pins  38 , although only three are shown in the plan view of FIG.  4 . More or fewer pins  38  may be used. When operatively positioned just forward of the threaded bearing  18 , the exterior surface  42  of the sleeve-and-pin assembly  16  is designed and contoured to slidingly engage interior surfaces  43  of the spindle adapter body  14  such that the sleeve-and-pin assembly  16  may slide axially relative to the spindle adapter body  14 . In the operational position of the sleeve-and-pin assembly  16 , the pins  38  extend in a direction generally parallel with the axis A of FIGS. 1 and 3. 
     Although the term “pins” is used with reference to the sleeve-and-pin assembly  16 , the function of the “pins” shown in the Figures may be performed by rearwardly-extending projections of any shape, and the threaded bushing  18  may be provided with apertures or passages of any appropriate size or shape to accommodate those projections. 
     When the sleeve-and-pin assembly  16  is operatively positioned, a set of wave wire springs  44  (Smalley Steel Ring Company, Lake Zurich, Ill., USA) are inserted between the sleeve-and-pin assembly  16  and the spindle adapter body  14  such that they bear against the forward flange surface  46  of the sleeve-and-pin assembly  16  and the corresponding interior vertical bearing surface  48  of the spindle adapter body  14 . (Wave wire springs  44  are compression springs formed with a single turn of spring wire that has a plurality of distinct waves therein.) In the illustrated embodiment, two wave wire springs  44  are provided, each wave wire spring  44  capable of resiliently resisting, for example, an applied force of about 200 pounds. The two wave wire springs  44  are separated by a washer  50 . (Together, the two wave wire springs  44  are capable of resiliently resisting a force of about 400 pounds.) More wave wire springs  44  could be used in series if additional force bias is desired. The wave wire springs  44  provide a resilient spring bias that biases the pin-and-sleeve assembly  16  rearwardly, such that the pins  38  contact the drawbar link-up  20  and the drawbar link-up  20  moves the sleeve-and-pin assembly  16  forward against the bias of the wave wire springs  44 . The wave wire springs  44  provide a relatively large spring bias and require relatively little space. However, conventional compression springs may be used if more space is provided for their installation. 
     As shown in FIGS. 1 and 2, the sleeve-and-pin assembly  16  is configured to receive the collet head  22  such that interior cam surfaces  52  of the sleeve-and-pin assembly  16  slidingly engage corresponding cam surfaces  54  of the collet head  22 . Although the cam surfaces  52 ,  54  illustrated in the Figures are frustro-conical and of continuous slope, other types of cam surfaces may be used. In general, any engaging, motion-translating surface may be used as a cam surface. The collet head  22  extends rearwardly from the front opening  56  of the sleeve-and-pin assembly  16 , beyond the flanged rear portion  40  of the sleeve-and-pin assembly  16 , and is held in an axially fixed position by the keyscrew  32 , as described above. 
     The sleeve-and-pin assembly  16  also provides two circumferential grooves  58  which are constructed and arranged to accommodate o-ring-type wiping seals  60 . The seals  60  prevent debris from lodging between the sleeve-and-pin assembly  16  and the spindle adapter body  14  by sealingly engaging the spindle adapter body  14 . The interface between the sleeve-and-pin assembly  16  and the spindle adapter body  14  may be lubricated with a suitable viscous grease, in which case the seals  60  would also prevent the grease from leaking. 
     The operation of the collet assembly  10  can be seen in FIG. 1, in which the collet head  22  is in a closed, workpiece-gripping position, and in FIG. 3, in which the collet head  22  is in an open position. In the workpiece-gripping position of FIG. 1, the drawbar link-up  20  is extended forwardly and is in contact with the pins  38  of the sleeve-and-pin assembly  16 . The position of the drawbar link-up  20 , and the resulting force on the pins  38  and the sleeve-and-pin assembly  16 , forces the sleeve-and-pin assembly  16  forward against the spring bias of the wave wire springs  44 . (The wave wire springs  44 , which are shown partially in phantom, are partially compressed in the view of FIG. 1.) The sliding engagement of the cam surfaces  52 ,  54  of the collet head  22  and the sleeve-and-pin assembly  16  forces the circumferentially-spaced segments of the collet head  22  closer together, which decreases the diameter of the order hole  56  of the collet head  22 . The amount of axial travel between the positions illustrated in FIGS. 1 and 3 may be, for example, about {fraction (1/16)} inch. 
     FIG. 3 shows the open position of the collet head  22 . In FIG. 3, the drawbar link-up  20  is retracted and is thus not driving the pins  38  of the sleeve-and-pin assembly  16  forward. Consequently, because there is substantially reduced force on the pins  38  (and thus, the sleeve-and-pin assembly  16 ), the spring bias of the wave wire springs  44  forces the sleeve-and-pin assembly  16  to retract rearwardly. (The wave wire springs  44  are substantially uncompressed in FIG. 3, relative to their position in FIG. 1.) As the sleeve-and-pin assembly  16  retracts, the sliding engagement of its cam surfaces  52  with the cam surfaces of the collet head  22  cause the distance between the circumferentially-spaced segments of the collet head  22  to increase, which increases the diameter of the order hole  56  of the collet head  22 . 
     Because the collet head  22  is held in an axially fixed position by the threaded bushing  18 , there is no need to provide a cap or cap assembly for the collet assembly  10 . In general, the collet assembly  10  may be used with a variety of standard collet heads  22 , including, for example, the 5C, 16C, 20C, 25C, and 3J. (Sold, for example, by Hardinge, Inc., Elmira, N. Y., USA.) Additionally, because no direct connection is required between the drawbar link-up  20  and the spindle adapter body  14 , the components within the spindle adapter body  14  may be assembled and precisely adjusted during manufacture, independent of installation on a machine. Precise adjustment of the spindle adapter body  14  and its components during manufacture makes field installation easier than with prior art collet assemblies. Additionally, the link-up  20  itself is easily installed on a user&#39;s turning machine. 
     With the exception of the wave wire springs  44 , the components of the collet chuck assembly  10  are typically machined from mild steel to appropriate tolerances and then heat-treated to desired hardnesses and/or other material properties. The various components may be made in a variety of sizes in order to accommodate differently-sized collet heads  22 . 
     Although the invention has been described with respect to exemplary embodiments, those of ordinary skill will realize that variations and modifications are possible within the scope of the invention. The embodiments described herein are intended to be exemplary only and are not to be construed as limiting.