Abstract:
A collet adapter operates a draw-type collet in an axially stationary mode in a machine spindle that would otherwise operate with a stationary collet. The machine spindle has an axially stationary outer portion including a cap nut and an axially movable sleeve inside the axially stationary portion. The collet adapter includes an adapter body and a restraining apparatus. The adapter body has an outside surface that fits into the axially movable sleeve such that adapter body moves axially with the axially movable sleeve. The adapter body has an inside surface that receives the draw-type collet in sliding engagement. The restraining apparatus is configured to transmit an axial force from the stationary cap nut to a rearward portion of the draw-type collet to restrain axial motion of the draw-type collet. As a result of this axial constraint forward and backward motion of the axially movable sleeve closes and opens the collet respectively through the sliding engagement between the collet and the inside surface of the adapter body.

Description:
FIELD OF THE INVENTION 
     The invention relates to lathe components and particularly to the mechanical interface between a collet and a lathe spindle. More particularly, the invention relates to an adapter that enables a small draw-type collet to be operated as an axially stationary collet having a spindle sleeve that is ordinarily utilized with a larger axially stationary-type collet. 
     BACKGROUND 
     A lathe is a rotational metal machining tool that is commonly used in manufacturing and prototyping articles having a degree of cylindrical symmetry prior to other processes. The lathe includes a spindle and a cutting tool. An article to be machined, referred to as a workpiece, is securely mounted in the spindle. The spindle then spins, rotating the workpiece. The cutting tool is then manipulated to impinge upon the workpiece whereby it makes circular cuts into the workpiece. Mounting and manipulation of the cutting tool is used to control a cylindrical cut geometry that defines resultant geometrical modifications of the article by the lathe. 
     The subject of this invention relates to the spindle and an adaptive apparatus for mounting the workpiece in the spindle. Spindles come with work-holding apparatuses of various types including jaw-type chucks and collets. A collet is typically used for a small to medium sized workpiece. Collets come in various types including draw-in collets, stationary collets, and expanding collets. This invention relates to the draw-in and stationary collets. The following discussion concerning  FIGS. 9A and 9B  will be helpful in understanding the invention. 
     For future descriptions the terms forward and rearward are used. Forward always refers to an axial direction (along the axis of spindle rotation) out of the spindle. Rearward always means the opposite of forward. To illustrate this convention a workpiece is inserted into a collet in the rearward direction and removed in the forward direction. 
       FIG. 9A  illustrates a cross-sectional view of a spindle  100  including an axially stationary spindle sleeve  102  and draw-in collet  104 . After a workpiece is placed in collet  104  a draw tube  106  attached to collet  104  pulls collet  104  rearward (to the left in the figure, into the spindle). As this happens, a flared zone of sleeve  102  bears radially inwardly upon a similarly flared zone of collet  104  in order to close collet  104  upon the workpiece. The sleeve  102  remains axially fixed while the collet  104  is pulled axially in a rearward direction. The process of closing a draw-in collet  104  has an axial positional component that decreases accuracy in axial location. 
       FIG. 9B  illustrates a cross sectional view of a spindle  200  including an axially movable spindle sleeve  202  and a stationary collet  204 . Surrounding the axially movable spindle sleeve  202  is a fixed portion  206  of spindle  200  including cap nut  208 . After a workpiece is placed in collet  204 , the spindle sleeve  202  moves forward. As this happens, a flared zone of sleeve  202  bears radially inwardly upon a similarly flared portion of collet  204  in order to close collet  204  to provide clamping force upon the workpiece. During this process collet  204  remains stationary, being held in place by cap nut  208  which is part of the fixed portion  204  of spindle  200 . In contrast to the draw-in collet, the stationary collet closure does not have an axial positional component. Because of this, stationary collets are preferable for some manufacturing operations and for machining that requires high axial precision. 
     Lathes are generally used in fabricating articles having a wide range of diametrical sizes. The size of the spindle generally correlates with the maximal diameter of a workpiece. This invention concerns a need to fabricate relatively small articles such as small mechanism components and dental implants. Ideally smaller lathes are used for smaller parts. However there are economical and delivery rate reasons why a shop would like to be able to use larger lathes for small parts. For example, if a shop has a number of currently under-utilized larger lathes, an order for smaller articles can be accomplished more quickly if all the idle lathes can be used. 
     There is also a motivation to be able to machine a small workpiece as close as possible to an axial location at which the workpiece is supported by the collet. When conventional stationary collets are used the distance between axial collet support and machining may become too large such that the workpiece is not adequately supported. The spindle cap design generally used for stationary collets is inherently bulky in diameter and also necessitates an axial extension of the work zone away from the flared clamping area. These aspects degrade workpiece clamping force at the point of machining and necessitate the extension of cutting tools, which reduces strength, rigidity, and accuracy. What is needed is a way of machining such a small diameter workpiece very close to the support zone. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is an isometric view of a collet adapter  2  with a collet  4  installed. 
         FIG. 2  is a front view of a collet adapter  2  with a collet  4  installed. 
         FIG. 3  is a cross sectional view of a collet adapter  2  taken from section A-A of  FIG. 2 . 
         FIG. 4  is a cross sectional view of a collet adapter  2  taken from section B-B of  FIG. 2 . 
         FIG. 5  is an exploded view of adapter  2  holding collet  4 . 
         FIG. 6  is a front view of a spindle  72  having collet adapter  2  with collet  4  installed. 
         FIG. 7  is a cross sectional view of spindle  72  taken from section C-C of  FIG. 6 . 
         FIG. 7A  is a detail view taken from  FIG. 7  depicting the collet  4  in an open state. 
         FIG. 7B  is a detail view taken from  FIG. 7  depicting the collet  4  in a closed state. 
         FIG. 8A  is a detail view taken from  FIG. 7A  depicting the interactions between portions of the adapter. 
         FIG. 8B  is a detail view taken from  FIG. 7B  depicting the interactions between portions of the adapter. 
         FIG. 9A  is a cross sectional view illustrating a draw-in type collet  104  installed in a spindle  100 . 
         FIG. 9B  is a cross sectional view illustrating an axially stationary type collet installed in spindle  200 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1-5  depict a collet adapter  2  of the present invention.  FIG. 1  is an isometric view of collet adapter  2  holding draw-in type collet  4 .  FIG. 2  is a front view of adapter  2  holding collet  4 .  FIG. 3  is a sectional view of adapter  2  holding collet  4  taken from section A-A of  FIG. 2 .  FIG. 4  is a sectional view of adapter  2  holding collet  4  taken from section B-B of  FIG. 2 . Section  5  is an exploded view of adapter  2  holding collet  4 . 
     Collet adapter  2  is configured to enable a relatively larger lathe to accommodate a small workpiece  6  and to machine an article thereby with high axial precision and to allow for machining of the workpiece very close to an axial zone of support. Collet adapter  2  is configured to receive a draw-in collet  4  and to fit into a spindle sleeve configured for an axially stationary collet. Thus, collet adapter  2  converts a relatively small draw-type collet  4  into a larger diameter stationary closure collet. Thus draw-in type collet  4  remains axially stationary relative to fixed portions of the spindle as collet  4  is being opened or closed. The use of the draw-in type collet  4  allows the cutting tools to access the workpiece  6  as close to the collet support as possible. 
     Referring to  FIGS. 1 and 2 , some directions and cylindrical coordinate axes are depicted including a Z-axis and radius R. Generally the Z-axis is disposed along the axis of rotation of a lathe spindle when collet adapter  2  is mounted in the spindle. The direction positive Z refers to a “forward” direction of removing a workpiece  6  from collet  4  which is the direction a spindle sleeve moves to close collet  4 . The direction negative Z refers to a direction of placing workpiece  6  into collet  4  which is the direction that a spindle sleeve moves to open collet  4 . The direction R refers to a radial direction that is perpendicular to the axis of rotation Z. An angular value of theta (not shown) concerns rotation about the axis of rotation Z. 
     Generally speaking this description will refer to “outside” surfaces and “inside” surfaces of various portions of adapter  2 . Generally “inside” surfaces are those which at least partially enclose a cavity and/or have surface portions that face toward decreasing values of R. Opposing “outside” surfaces tend to face toward increasing values of R except where they are parallel to R. 
     Referring to  FIGS. 1 and 3 , adapter  2  includes adapter body  8  which defines an outside surface  10  and an inside surface  12 . Outside surface  10  is configured to be received inside an axially moveable sleeve of a lathe spindle. Inside surface  12  is configured to receive collet  4  and contains components of adapter  2 . 
     Referring to  FIGS. 1 and 5 , adapter body  8  includes a rearward portion  14 , forward portion  16 , and a flared portion  18  between rearward portion  14  and forward portion  16 . Rearward portion  14  has an outer diameter that is greater than an outer diameter of forward portion  16 . Flared portion  18  has an outer diameter that increases in a forward or +Z direction. Flared portion  18  slopes outwardly radially from rearward portion  14  and includes a circular face  22  at a forward end. Circular face  22  generally faces in the forward direction +Z. 
     Referring to  FIGS. 3 and 5 , a plurality of connecting holes  24  pass from circular face  22  to inside surface  12  of adapter body  8 . The connecting holes  24  define openings on circular face  22  and define openings on the inside surface  12 . 
     Inside surface  12  of adapter body  8  includes a tapered inside portion  26  that has an inside diameter that decreases in the rearward direction. Tapered portion  26  of inside surface  12  is configured to engage a flared portion  28  of collet  4  in order open and close collet  4  about workpiece  6 . 
     Adapter body  8  moves rearward to open and forward to close collet  4 . A spring assembly  30  (see  FIG. 5  in particular) is configured to urge adapter body  8  rearward relative to collet  4 . Spring assembly  30  ( FIGS. 3 and 5 ) is disposed within thrust stop sleeve  32  which is also within the rearward portion of adapter body  8 . Spring assembly  30  includes spring  34  and spacer tube  36 . Spacer tube  36  has a rearward portion  38  and a forward portion  40 . Forward portion  40  has a larger outer diameter than rearward portion  38 . Spring  34  fits on the rearward portion  38  and is accommodated by a diametrical difference between the forward portion  40  and the rearward portion  38 . Spring  34  generates an urging force between a rearward end of thrust stop sleeve  32  and forward portion  40  that in turn urges adapter body  8  in a rearward direction relative to collet  4 . Thus spring  34  and spring assembly  30  urge the adapter body in a rearward direction that serves to open collet  4 . 
     Referring to  FIGS. 3 and 5 , restraining apparatus  20  includes draw nut  42 , thrust collar  44 , and a plurality of thrust linkage rods  46 . Draw nut  42  is configured to be threadedly mounted to a rearward portion of collet  4 . Restraining apparatus  20  ( FIG. 5 ) is configured to couple collet  4  to an axially fixed portion of a lathe spindle. In the illustrated embodiment, restraining apparatus  20  is an assemblage of machine parts that transmit a restraining force through adapter body  8  between an axially fixed portion of a spindle and collet  4 . The restraining force maintains collet  4  in an axially stationary location as collet  4  is being closed by forward motion of adapter body  8 . 
     The assemblage of machine parts  20  that define the restraining apparatus  20  transmit the restraining force by the cooperation of the individual parts including the draw nut  42  at one end of the assemblage  20  and the thrust collar  44  at the other end of the assemblage  20 . The thrust linkage rods  46  transmit the restraining force between the thrust collar  44  and the draw nut  42 . The thrust collar engages an axially stationary cap nut  78  ( FIGS. 7 and 8 ) and the draw nut  42  engages collet threads  5  at a rearward portion  43  of collet  4 . Thus the assemblage  20  thereby transmits the restraining force from the axially stationary cap nut  78  to the rearward portion  43  of collet  4 . 
     Thrust collar  44  mounts to forward portion  16  ( FIG. 1 ) of adapter body  8 . Thrust collar  44  includes a forward portion  48  and rearward flange  50 . Forward portion  48  of thrust collar  44  extends forwardly along the forward portion  16  of adapter body  8 . Flange  50  extends radially outwardly and defines forward flange face  52  and rearward flange face  54 . Forward flange face  52  is configured to engage a cap nut  78  on an axially fixed portion of a spindle. 
     Thrust linkage rods  46  are configured to transmit the restraining force from thrust collar  44  to the draw nut  42 . Each thrust linkage rod  46  passes through and spans a connecting hole  24  ( FIG. 5 ). Each thrust linkage rod  46  has a forward end  56  and a rearward end  58 . The forward end  56  of each thrust linkage rod  46  is configured to engage rearward flange face  54 . The rearward end  58  of each thrust linkage rod is configured to engage draw nut  42 . Thus, as part of assemblage  20 , the thrust linkage rods  46  transmit the restraining force through adapter body  8 . 
     Referring to  FIGS. 4 and 5 , adapter  2  includes mounting posts  60  that couple thrust collar  44  to adapter body  8 . Adapter  2  also includes a keying ring  62  including a radially inwardly projecting tab  64  configured to engage a slot  66  in collet  4 . Tightening set screw  68  applies a force on pressure pellet  70  which in turn rotationally locks keying ring  62  into position. This constrains the relative motion of adapter body  8  and collet  4  to axial motion due to the tab  64  and slot  66  interaction. 
     Referring to  FIG. 3 , an engagement between thrust stop sleeve  32  and draw nut  42  puts a limit on closure of collet  4 . The amount of maximum closure is determined according to the position of draw nut  42  upon collet threads  5  ( FIG. 5  also). The keying ring  62  is used to set this maximum closure. The tab  64  prevents rotation about axis Z when the set screw  68  is tightened, thus maintaining a maximum closure setting. 
       FIGS. 6, 7, 7A, 7B, 8A, and 8B  depict collet adapter  2  installed in the spindle of a lathe.  FIG. 6  depicts a front view of spindle  72  with collet adapter  2  having collet  4  installed.  FIG. 7  is a cross sectional view taken from section C-C of  FIG. 6 .  FIG. 7A  is a detailed view taken from  FIG. 7  with collet  4  in the open state in which workpiece  6  can be easily inserted and removed from collet  4 .  FIG. 7B  is a detailed view taken from  FIG. 7  with collet  4  in a closed state in which workpiece  6  is firmly clamped in collet  4 .  FIGS. 8A and 8B  are further detailed views taken from  FIGS. 7A and 7B  respectively to provide a more detailed view of the interaction of various portions of the illustrated system. 
     Referring to  FIG. 7 , spindle  72  includes an outer portion  74  that is axially stationary and spindle sleeve  76  that is axially movable within outer portion  74 . The axially stationary outer portion  74  also includes a cap nut  78  that is attached to spindle  72  through inter-engaged screw threads. Thus cap nut  78  forms a portion of the axially stationary portion  74  of spindle  72 . 
     Preparing the adapter and collet for use: The collet  4  is first assembled to the adapter  2 . Refer now to  FIG. 5 . The collet  4  is assembled to the adaptor  2  by linearly inserting the collet  4  into adapter  2  and then rotating the collet  4  clockwise. As the collet  4  is linearly inserted into adapter body  8 , tab  64  extending from keying ring  62  engages slot  66  in collet  4 . Keying ring  62  is initially free to rotate. When collet  4  is rotated clockwise, outer threads  5  on collet  4  engage inner threads  43  on draw nut  42 . 
     The progressive clockwise engagement determines the location of draw nut  42  upon collet threads  5 . The location of draw nut  42  upon collet  4  constrains a distance axial of motion between adapter  2  and collet  4 . Thus, the draw nut location determines the maximum closure of collet  4 . This can be quite important for very small diameter delicate parts that may become damaged if the closure force of collet  4  is too high. Therefore the axial location of draw nut  42  upon collet  4  is fixed by the action of set screw  68 , pressure pellet  70 , and keying ring  62 . 
     When the threads  5  and  43  are properly engaged to provide an optimal closure of collet  4 , the set screw  68  is turned clockwise; the set screw bears inwardly on pressure pellet  70  which in turn bears inwardly upon keying ring  62  to lock it in place so that it cannot rotate about axis Z. Locking keying ring  62  in place constrains relative motion between collet  4  and adapter body  8  to the axial direction Z due to the action of tab  64  in slot  66 . Thus the collet  4  is thereby assembled to the adapter  2 . 
     Preparing the spindle for use (refer to  FIG. 7 ): The cap nut is  78  is unscrewed and removed from spindle  72 . Next, the rearward portion  14  ( FIG. 1 ) of adapter  2  is then linearly placed into spindle sleeve  76 . Finally, the cap nut  78  is screwed back on to spindle  72 . 
       FIGS. 7A and 7B  depict open and closed states of collet  4 . According to  FIG. 7A , spring  34  exerts a force between collet  4  and adapter body  8  thereby urging adapter body in a rearward (−Z) direction. This leaves collet  4  open such that workpiece  6  may be inserted. Referring to  FIG. 8A  there is initially a gap  80  between draw nut  42  and thrust stop sleeve  32 . The location of draw nut  42  upon collet  4  defines gap  80 . This gap defines an allowed range of axial motion of adapter body  2  with respect to collet  4  and thereby defines the maximal closure of collet  4 . 
     The lathe grips the workpiece  6  by propelling the spindle sleeve  76  in a forward direction. As spindle sleeve  76  moves forward (+Z direction), it engages the flared portion  18  of adapter body  8 . Once engaged spindle sleeve  76  and adapter body  8  move forward together. As adapter body  8  moves forward the tapered inside surface  26  of adapter body  2  slidingly engages flared portion  28  of collet  4 , putting radially inward pressure on collet  4  (since collet  4  is axially stationary). Thus collet  4  closes upon workpiece  6  as depicted in  FIG. 7B . 
     Comparison of  FIGS. 8A and 8B  illustrate the effect of forward motion of adapter body  8  under the influence of spindle sleeve  76 . The forward motion is relative to stationary elements including cap nut  78 , thrust collar  44 , thrust linkage rods  46 , draw nut  42 , and collet  4 . Initially there is a gap  80  defined between thrust stop sleeve  32  and draw nut  42 . During forward motion the thrust stop sleeve  32  moves forward until it engages draw nut  42 . Once thrust stop sleeve  32  is engaged with draw nut  42  the forward motion of adapter body  8  is thereby halted. Thus the initial gap  80  defines the extent of the forward motion and hence defines a controlled and maximal closure of collet  4 . 
     As adapter body  8  is being pushed forward by spindle sleeve  76  the restraining apparatus  20  ( FIG. 5 ) restrains motion of collet  4  so that collet  4  remains stationary in axial direction Z. Restraining apparatus  20  is axially coupled to cap nut  78  (part of the fixed portion  74  of spindle  72 ) and to collet  4 . 
     In the illustrated embodiment restraining apparatus  20  ( FIG. 5 ) includes an assemblage including draw nut  42 , thrust linkage rods  46 , and thrust collar  44  (see also  FIG. 3 ). This assemblage  20  transmits a restraining force from cap nut  78  to collet  4  to prevent axial motion of collet  4  while collet  4  is being closed. The restraining force is transmitted from cap nut  78  to radially extending flange  50  of thrust collar  48  to linkage rods  46  to draw nut  42  which in turn secures the axial location of collet  4 . 
     Stated another way: (1) the collet is held in place by an axial counter force exerted by draw nut  42 ; (2) the counter force is imparted to the draw nut  42  by thrust linkage rods  46 ; (3) thrust linkage rods  46  are abutted against a bearing surface provided by radially extending flange  50  of thrust collar  48 ; radially extending flange  50  of thrust collar  48  is abutted against cap nut  78 . 
     The lathe releases the workpiece  6  by propelling the spindle sleeve in a backward (−Z) direction. The spring  34  can now push the adapter body  8  in a backward (−Z) direction thus allowing the collet  4  to open. 
     While all of the fundamental features and characteristics of the collet adapter  2  have been disclosed and described, with reference to particular embodiments thereof, a latitude of modification is envisioned. Various changes and substitutions are intended in the foregoing disclosure and it will be apparent that some features of the invention will be employed without a corresponding use of other features without departing from the scope of the invention as set forth. It should be understood that such substitutions, modifications, and variations may be made by those skilled in the art without departing from the spirit or scope of the invention. Consequently all such modifications and variations are included in the scope of the invention as defined thereof except as defined by the claims.