Patent Publication Number: US-6988388-B2

Title: Thread rolling attachment

Description:
TECHNICAL FIELD 
     The present invention relates generally to the field of thread rolling attachments for machine tools, and more particularly, to an improved thread rolling attachment that is adapted to be mounted on a machine tool and to be selectively moved in an axial direction relative to a workpiece having a cylindrical surface on which a thread is to be rolled. 
     BACKGROUND ART 
     It is often desired to roll a thread onto a workpiece. There are a number of ways of doing this. In some cases, thread rolls are moved tangentially into engagement with the cylindrical surface of a workpiece onto which a thread is to be rolled. In other instances, the thread rolls are moved axially into position along side the workpiece, and are then moved radially inwardly to engage the workpiece and to roll the thread thereon. 
     According to still another technique, an attachment is provided on a machine tool. The attachment has three thread rolls that are movable radially between engaged and disengaged positions. Initially, the three thread rolls are moved radially inwardly to an engaged position. The workpiece is then feed axially into the space between the three rolls, either through movement of the workpiece relative to the attachment or vice versa, and a thread is progressively rolled onto the workpiece. When the end of the workpiece abuts a stop, a triggering mechanism causes the spring-biased thread rolls to quickly move radially outwardly so as to disengage themselves from the workpiece and to allow the workpiece to be withdrawn from the attachment. 
     One such type of end working attachment is shown and described in U.S. Pat. No. 5,568,743, which issued on Oct. 29, 1996 to Wilhelm Fette GmbH. This patent discloses in  FIG. 1 , a conventional prior art end working attachment of the type heretofore described. 
     Other types of thread rolling attachments and implements are shown and described in U.S. Pats. No. 2,909,087, 3,352,139, 3,365,924 and 4,771,625. The disclosure of all five of the above patents is hereby incorporated by reference insofar as their descriptions of the structure and operation of prior art thread rolling attachments is concerned. 
     Upon information and belief, one problem that accompanies the use of the device shown in FIG. 1 of the Fette &#39;743 patent, is that the front plate is relatively thin and flexible, and may distort in use. This can adversely affect the shape and profile of the threads that are rolled onto a workpiece. 
     Accordingly, it would be generally desirable to provide an improved thread rolling attachment of the same general type, that would have increased rigidity, and would be less susceptible to distortion. 
     DISCLOSURE OF THE INVENTION 
     With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved thread rolling attachment ( 50 ) that is adapted to be mounted on a machine tool and to be selectively moved in an axially direction relative to a workpiece. 
     The workpiece has a cylindrical surface on which a thread is to be rolled. The attachment has a spring housing ( 56 ), a sun gear ( 60 ) rotatably mounted on the spring housing, and three planetary gears ( 61 ,  61 ,  61 ) matingly engaging the sun gear at equidistant locations thereabout. A torsional spring ( 59 ) acts between the spring housing and the sun gear. 
     In this form, the improvement broadly comprises: a center plate ( 62 ) having three circularly-spaced detents ( 82 ,  82 ,  82 ); a front plate ( 66 ) having a central portion ( 70 ) arranged in axially-spaced relation to the center plate and having three circularly-spaced lugs or projections ( 71 ) extending toward the center plate such that the distal end surfaces of such lugs or projections are adapted to engage the center plate when the device is assembled; a recess ( 73 ) extending into each lug from such distal surface, each recess being adapted to receive a respective one of the detents for angularly orienting the center and front plates relative to one another; three eccentric roll pins ( 63 ,  63 ,  63 ) having their opposite marginal end portions journalled on the center and front plates and being spaced equally from one another about an imaginary circle; a thread roll ( 65 ) rotatably mounted on each eccentric roll pin; and a plurality of fasteners ( 68 ) operatively arranged to selectively hold the center and front plates together; whereby, when the thread rolling attachment is assembled, the front plate will have improved rigidity and will be less susceptible to deformation in use. 
     The center and front plates may be provided with a low friction coating. The axes of the roll pins may be skewed with respect to the longitudinal axis of the workpiece and the cylindrical surface thereon. Moreover, a carbide bushing may be operatively arranged between each thread roll and its associated roll pin. 
     Accordingly, the general object of the invention is to provide an improved thread rolling attachment. 
     Another object is to provide an improved end working attachment that is adapted for use in a machine tool, for rolling a thread onto a workpiece. 
     Still another object is to provide an improved end-working thread-rolling attachment which is more durable, more rigid, and less susceptible to deformation in use. 
     These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric exploded view of a prior art thread rolling attachment, this view being substantially the same as that shown in U.S. Pat. No. 5,568,743. 
         FIG. 2  is an isometric exploded view of an improved thread rolling attachment incorporating the present invention. 
         FIG. 3  is an isometric rear view of the front plate shown in  FIG. 2 . 
         FIG. 4  is a rear elevation of the front plate shown in  FIG. 3 . 
         FIG. 5  is a fragmentary vertical sectional view of the front plate, taken generally on line  5 — 5  of  FIG. 4 . 
         FIG. 6  is a fragmentary horizontal sectional view of the front plate, taken generally on line  6 — 6  of  FIG. 4 . 
         FIG. 7  is an isometric front view of the center plate shown in  FIG. 2 . 
         FIG. 8  is a front elevation of the center plate shown in  FIG. 7 . 
         FIG. 9  is a fragmentary vertical sectional view of the center plate, taken generally on line  9 — 9  of  FIG. 8 . 
         FIG. 10  is a fragmentary vertical sectional view of the center plate, taken generally on line  10 — 10  of  FIG. 8 . 
         FIG. 11  is a side elevational view of one of the eccentric roll pins. 
         FIG. 12  is a top plan view of the eccentric roll pin shown in  FIG. 11 . 
         FIG. 13  is a right end elevation of the eccentric roll pin shown in  FIG. 11 . 
         FIG. 14  is a side elevational view of one of the carbide roll bushings. 
         FIG. 15  is a left end elevation of the bushings shown in  FIG. 14 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure normally faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
     Prior Art Attachment ( FIG. 1 ) 
     Referring now to the drawings, and more particularly, to  FIG. 1  thereof, a conventional axial thread rolling head, such as shown in FIG. 1 of U.S. Pat. No. 5,568,743, is depicted as including a bearing unit  20  and a shank  21 . Shank  21  is adapted to be clamped into the spindle of a numerically-controlled machine tool (not shown). The shank broadly includes a coupling portion  22 , a cylindrical bearing portion  23 , and a spline connection portion  24 . 
     The bearing unit includes three profile rollers, severally indicated at  25 . Each roller is supported on an eccentric shaft, one of which is indicated at  26 . The marginal end portions of eccentric shafts  26  are received in corresponding bores provided in a front plate  28  and a center plate  29 , respectively. Front and center plates  28 ,  29  are spaced from one another by three specially-configured bolts, severally indicated at  30 . The threaded shank portion of each bolt  30  extends through a corresponding bore provided in center plate  29 . The thread rollers  25  are rotatably supported on the eccentric shafts  26 , which, at their rear ends, are shown as being flattened. These flattened ends cooperate with complementarily-configured holes in planetary gear wheels  31  meshing with a central sun gear  32 . The central sun gear is mounted on the spline connection portion  24  of shaft  21 . Rotation of the central sun gear  32  causes the three planetary gears  31 ,  31 ,  31 , and the three eccentric shafts  26 ,  26 ,  26  mounted thereon, to rotate. Rotation of the eccentric shafts  26  relative to the front and central plates results in a change of the radial distance of the outer surfaces of the profile rollers relative to the workpiece axis. The thread milling makes a preset distance between the profile rollers necessary. This radial distance must be selectively increased for removing the workpiece, indicated at W, from between the rollers. 
     A spring housing  33  provided with a central bore is arranged on a bearing portion  23 , and includes a claw clutch portion (not shown) which cooperates with the claw clutch portion  22  of shank  21 . A torsional spring  34  is arranged in the spring housing  33 . The outer end of spring  34  cooperates with a slot (not shown) within spring housing  33 . The inner end of the helical spring is connected to a portion (not shown) of shank  21 . A shank  35  is provided on the outer periphery of the spring housing. Shank  25  may be grasped and twisted with the spring housing if the claw clutch portions are out of mesh. Spring rings  36 ,  38  ensure the axial support of the bearing unit  20  on shank  21 . The threaded shank portions of bolts  30  extend through holes provided on the spring housing and bores through a disk  39 . The spring housing  53  is attached to central plate  29  by means of nuts  40 . 
     A bolt  41  is secured in shank  21  with the aid of two nuts  42 ,  43 . The axial position of bolt  41  within shank  21  is adjustable by virtue of its threaded connection within shank  21 . 
     The function of the prior art rolling head is as follows. The rollers  25  are initially spaced apart from one another at a preset radial distance while the claw clutch portions are in meshing engagement with each other. In this position, the torsional spring is wound. To mill a thread into a workpiece, the workpiece is guided axially between the radially-inwardly positioned rollers  25 , either by movement of the machine tool spindle relative to the workpiece or vice versa. The workpiece moves into the rolling head until its end face abuts the end face of bolt  41 . In this way, the feed of shank  21  is terminated together with the bearing unit  20  and the bearing unit  20  itself continues moving as a result of the described feed. This causes the claws of the claw clutch to get out of mesh and the spring housing  33 , and, consequently, the bearing unit  20  rotates in response to the action of spring  34 , this rotation being performed over preset angle of rotation as a result of the out-of-mesh portion of the claw clutch. This relative rotation of shank  21  and the bearing unit  20  causes the eccentric pins  26  to be rotated so that the profile rollers move radially outwardly to disengage from the workpiece. The workpiece can then be removed from the rolling head. 
     To lock the rolling head again, spring housing  33  must be rotated in the opposite direction by grasping of shaft  35  and rotating the spring housing until the claw clutch can again lock into place. 
     Improved Thread Rolling Attachment ( FIGS. 2–13 ) 
     Referring now to  FIG. 2 , an improved thread rolling attachment is generally indicated at  50 . This attachment is shown as broadly including, from left to right in  FIG. 2 : a nut  51 ; a threaded shaft  52 ; a stop screw body  53 ; a shank  54 ; a washer  55 ; a spring housing  56  having a stud  58  thereon; a torsional spring  59 ; a sun gear  60 ; three planetary gears, severally indicated at  61 ; a central plate  62 ; three eccentric pins, severally indicated at  63 ; three carbide bushings, severally indicated at  64 ; three thread rolls, severally indicated at  65 ; a front plate  66 ; and a plurality of fasteners, severally indicated at  68 , that are arranged to selectively and releasably hold the front plate to the center plate. 
     The structure to the left (i.e., to the rear) of the center plate is individually old. 
     The inventive portion relates to the center plate  62 , the front plate  66 , and the structure therebetween. 
     Referring now to  FIGS. 3–6 , the front plate  66  is shown as being a specially-configured member having an annular vertical front end face  69 . The front plate has a central portion  70  and three circularly-spaced lugs or projections, severally indicated at  71 , extending rearwardly from the outer margins of the central portion  70  toward the center plate. Each of these lugs has a cylindrically-segmented outer surface, severally indicated at  72 . A through-hole or recess, indicated at  73 , extends forwardly into each lug to accommodate and receive a locating or positioning detent on the central plate  62 , as described infra. The front plate has three openings, severally indicated at  74 , defined between the adjacent lugs. These openings are skewed at an angle with respect to the front plate longitudinal axis, as shown in  FIG. 5 , and are adapted to receive the front marginal end portions of eccentric pins  63 . A central opening, indicated at  75 , is provided to accommodate passage of the workpiece. 
     Referring now to  FIGS. 7–10 , the central plate  62  is also shown as being a specially-configured member having an annular vertical rear surface  80 , and a specially-configured front surface  81  arranged in spaced facing relation to the front plate. Three detents, severally indicated at  82 , extend forwardly from surface  81 , and are adapted to be received in front plate holes or recesses  73 . As best shown in  FIGS. 7 and 8 , three circularly-spaced recesses, severally indicated at  83 , each arranged at an angled skewed to the longitudinal axis of the assembly, are provided in the central plate. Each recess surrounds a hole  84 , which is adapted to accommodate and receive the rear marginal end portion of a respective one of the eccentric pins  63 . A central hole  85  extends through the central plate. The cocked recesses  83  give the impression that each surface  81  has three surfaces having the same general profile as the lugs on the front plate. In fact, the distal ends of the front plate lugs are adapted to bear against such complementarily-configured surfaces  81 . The detents  82  are provided with tapped through-holes, indicated at  86 . 
     Referring now to  FIGS. 11–13 , each eccentric pin  63  is shown as being a horizontally-elongated specially-configured member having a longitudinal axis x—x. The eccentric pins have an annular vertical left end face  90 , an annular vertical right end face  91 , an outer surface that sequentially includes a cylindrical portion  92  extending rightwardly from the outer marginal of left end face  89 , a leftwardly-facing annular vertical surface  93 , a cylindrical surface  94  generated about an axis other than axis x—x so as to form a cam surface, a rightwardly-facing annular vertical surface  95 , a horizontal cylindrical surface  96 , and a reduced-diameter cylindrical surface  98  continuing rightwardly therefrom to join the right end face  91 . Surface  98  has a flat  99  milled thereon. A pair of tapped blind holes are provided in the eccentric pin from either end face. 
     Referring now to  FIGS. 14 and 15 , bushing  64  is shown as being a specially-configured hollow tubular cylindrical member having an annular vertical left end face  100 , an annular vertical right end face  101 , an outer cylindrical surface  102 , and an inner cylindrical surface  103 . Bushing  64  is adapted to be slipped over the central surface  94  of an eccentric pin. 
     The device is assembled as shown in  FIG. 2 . The rear marginal end portions of the eccentric pins  63  are received in the holes  84  provided in the central plate. The carbide bushings  64  surround the central portions of the eccentric pins, and the thread-forming rolls  65  are slipped thereover. The front marginal end portions of the eccentric pins are received in front plate holes  74 . The front plate is mounted on the rear plate such that the rear plate detents  82  are received in the front plate recesses  73 . This functions to angularly orient the front plate relative to the rear plate. The distal ends of the front plate lug surfaces bear against center plate surfaces  81 . Thereafter, conventional screw-type fasteners  68  may be passed through the front plate openings  73  such that their threaded shank portions will be matingly received in center plate recess tapped openings  83 . 
     As can be seen, the improved thread rolling attachment has a front plate assembly that is substantially more rigid, and less susceptible to bending and deformation than in the prior art. Moreover, the front end center plates may be coated with suitable low friction coating. The carbide bushings afford long life to the assembly. In addition to this, the assembly may be assembled by means of standard fasteners  68 , rather then specially-machined spacers as in the prior art. Thus, the improved device offers the advantage of a reduced cost, as compared to the prior art. It may use the same thread rolls as in the prior art machine shown in  FIG. 1 . It is compact in size, and easily adjustable. 
     Modifications 
     The present invention expressly contemplates that many changes and modifications may be made. For example, the structure to the rear of the center plate may be readily changed or modified as desired. The shape and configuration of the various parts and components, specifically including the center plate, the front plate and the structure therebetween, may be changed or modified as desired. The materials of construction are not deemed to be particularly critical. 
     Therefore, while the presently preferred embodiment of the improved thread roll attachment has been shown and described, and some modifications and changes thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.