Gear rolling method and apparatus
United States Patent [191 Culver [451 Apr. 15, 1975 GEAR ROLLING METHOD AND APPARATUS [75] Inventor: lrven H. Culver, Playa Del Rey,  
 Calif.  
 [73] Assignee: Southwestern Industries, Inc., Los  
 Angeles, Calif.  
 [22] Filed: Aug. 31, 1973 [21] Appl. No.: 393,500  
 [52] US. Cl. 72/108; 72/102; 29/1592 [51] Int. Cl B2lh 5/02 [58] Field of Search 72/102, 108, 465;  
 [56] References Cited UNITED STATES PATENTS 9/1958 Hill 72/108 12/1972 Loos 72/102 Motz et a1 72/108 Zeldman et al. 29/1592 Primary ExaminerLowell A. Larson Attorney, Agent, or Firm-Christie, Parker &amp; l-lale [57] ABSTRACT In the cold rolling of fully-rolled finished gear teeth, the smooth periphery of a rotatable metal gear blank is forcefully engaged by the circumference of an appropriately arranged and profiled rotatable forming roll. The desired tooth-forming forceful engagement of the roll with the blank is established progressively over the several rotations of the blank. The initial engagement force is sufficient in view of the initial contact area to produce inelastic deformation of the blank material. However, the initial engagement force is of a magnitude substantially less than the ultimately desired engagement force.  
 37 Claims, 13 Drawing Figures PATENTEIJAPR 1 51975 3, 8778 273 saw 2 pr 4 PATENTEDAPR 1 51915 3,877, 273 saw u 95 1} GEAR ROLLING METHOD AND APPARATUS FIELD OF THE INVENTION This invention relates to gear forming and, more particularly, to the cold rolling of finished gear teeth in a virgin. i.e., substantially smooth, surface of a gear blank by the use of a forming roll in which all of the teeth on the roll are identical and are profiled along the entire length thereof to be substantially&#39; conjugate to the teeth to be formed in the gear blank.  
 REVIEW OF THE PRIOR ART At the moment, there are no commercially practiced procedures for the cold rolling of gear teeth by a continuous process in a virgin blank by the use of forming teeth of uniform and constant profile. Some prior patents such as U.S. Pat. Nos. 2,883,894, 3,159,062, 3,531,976, 3,540,108, 3,552,167, and 3,599,463, for example, at first glance appear to describe the formation of gear teeth in this manner. On analysis, however, in the context of other related patents or of associated non-patent literature, such descriptions are found to be illusive.  
  The closest description in the prior art to the procedures and apparatus contemplated by this invention is the use of forming rolls having variable profile teeth. Variable profile teeth may be provided either as plural sets of teeth on a single roll, or by identical teeth on a roll but in which the teeth are of variable profile axially of the roll. See, for example, US. Pat. Nos. 2,886,990, 3,580,027 and 3,611,772.  
  To date, the only commercially practiced and practical use of forming roll teeth of constant form is found in the technique of gear finishing in which cold rolling of partially shaped teeth is practiced to produce the finished teeth. In this instance, cold rolling of the gear teeth is an alternate to gear shaving.  
  Substantial savings in time and money can be realized by the formation of gear teeth by a continuous cold rolling process using forming rolls in which all teeth on the forming roll are uniform and have profiles substantially conjugate to the teeth to be formed. These advantages include savings in setup time of the gear rolling apparatus, ease of manufacture of the forming roll, and minimum workpiece preparation. Also, savings are to be realized in efficient usage of a minimum amount of the workpiece material.  
 BACKGROUND OF THE INVENTION The ability to fully cold roll a gear tooth depends principally upon the material to be rolled and upon the profile of the tooth to be formed. In other words, cold rollability is in principal part a function of how much material is to be plastically deformed and displaced, how far, and how well the material being rolled accepts or permits such displacement under permissible loads without destruction of the material while still providing acceptable properties in the finished gear. At present, with known metals, the principal criterion limiting commercial formation of fully cold rolled gear teeth is tooth profile, of which the pressure angle is the parameter most directly related to the amenability of the material to be cold rolled from a virgin blank.  
  At present, the United States standard pressure angle for power transmission gears and the like is The pressure angle is the slope of the gear tooth at the pitch diameter relative to a line radially 0f the gear, i.e., parallel to the tooth height. In earlier years, the standard pressure angle in the United States was 14.5 percent. Many gears of English manufacture have pressure angles of 28 or so. There is nothing sacred about the value assigned to the pressure angle. Rather. the pres sure angle is a relatively arbitrary parameter selected consistent with design choices and interchangeability of gears. As the pressure angle increases, the force applied to a driven tooth by a driving tooth is applied more radially of the driven gear so that, for driven torque levels, bearing loads increase.  
  In gears intended for use in transmitting motion, as opposed to the transmission of power, the pressure angle of the gear tooth is not a significant&#39;factor. In motion transmitting gear trains, the principal concerns are usually over backlash and continuity of motion transfer from gear to gear in the train. In such gears the pressure angle of the individual gear teeth can be large.  
  It has been found that for a given metal the cold rollability of gear teeth in an unprepared surface to a finished state varies nonlinearly with tooth-form pressure angle. The amount of material which must be moved by plastic deformation in cold rolling a gear tooth with a 30 pressure angle is substantially less than the amount of material which must be moved in rolling a 20 tooth; the distances the material must be moved is also significantly different in the same manner. The cold rollability ofa metal depends upon the metalurgical properties of the metal and upon the users to which the rolled gear is to be put. Thus, cold rollability is a composite of many factors including initial hardness of the metal, its work hardening properties, its malleability, ductility. yield point. and hardenability, as examples of properties of the metal itself, and also static and dynamic tooth loading pressures and tooth profiles, as examples of usage considerations. It will be apparent that a given metal may have good cold rollability for one usage, such as motion transmitting gears, but may have no or very little useful cold rollability characteristics for a different usage such as power transmission gears required to transmit cyclic torque loads of high magnitude.  
  It is believed that a significant aspect of this invention is the discovery and teaching that, whatever the usage considerations, significant advances in the commercial application and practice of cold rolling of gears, including the manufacture of fully cold rolled gears, can be realized by changing the gear tooth design to teeth having larger pressure angles consistent with the metals available. In the context of the metals now available and their rollability, this invention teaches that gear teeth may be fully cold rolled from a virgin surface to a fully finished state by use of forming rolls in which all teeth are identical and are profiled substantially conjugate to the teeth to be rolled, if the teeth to be formed have pressure angles of about 28 or greater.  
  Another aspect of this invention, in the context of fully cold rolled gear teeth, concerns the rate at which the metal deforming forces are applied to the gear blank by a forming roll. This aspect of the invention is referred to herein as the soft start.&#34; The soft start features are especially useful where the gear rolling apparatus is of a centerless nature, or where the gear blank is mounted for rotation about a fixed axis but one of either the gear blank or the forming roll is undriven, in a positive sense, relative to the other. The centerless rolling and idling blank features are still other aspects of this invention.  
  In conventional machines for fully cold rolling gears and the like, the gear blanks and forming roll or rolls are inter-geared so that the blank and rolls are all positively driven at predetermined relative rpms. See for example, U.S. Pat. Nos. 2,883,894, 2,886,990, and 3,580,027. In such machines, the forming rolls and the gear blank can be brought together under full forging force without significant adverse effect in terms of the number of teeth to be formed on the gear. Where centerless or idling blank procedures are followed. engagement of the roll and the blank initially at full forming or forging force can easily result in the wrong number of teeth being formed in the gear; often such full-force V SUMMARY OF THE INVENTION This invention provides improvements in apparatus and procedures for the cold rolling of gear teeth in a virgin surface of gear blank to a finished state. Such cold rolling of gear teeth is accomplished by the use of forming rolls in which the forming teeth are all identical and are of constant profile along their length on the forming roll. The forming roll teeth have profiles which are essentially conjugate to the teeth to be formed. This invention, thus broadly summarized, includes method and apparatus in which only one of the gear blank and the forming roll are positively driven, the other of the blank and the roll being rotated in response to engagement with the positively driven element. The centerless rolling procedures and apparatus described herein are a form of the idling blank aspect of this invention. These features of this invention result in the ability to fully cold roll gear teeth by the use of apparatus which is substantially simplified over and less expensive than the gear rolling machines previously described and presently commercially available. This invention is applicable to the cold rolling of gears for use in power transmissions gear trains or motion transmitting gear trains from the smallest pinion gear to relatively large gears such as are used in automotive transmissions and the like.  
  Generally speaking, a principle claimed aspect of this invention pertains to the cold rolling of finished gear teeth in the smooth peripheral surface of a rotatable metal gear blank. The periphery of the gear blank is forcefully engaged by the circumference of an appropriately arranged and profiled rotatable forming roll. In this context, the improvement comprises establishing the desired tooth forming forceful engagement of the roll with the blank progressively from an initial engagement force over several rotations of the blank. The initial engagement force is sufficient, in view of the initial contact area provided between the roll and the blank, to produce inelastic (i.e., plastic) deformation of the blank material. The initial engagement force, however, is of a magnitude which is substantially less than the ultimately desired engagement force.  
 TERMINOLOGY As used herein the terms virgin blank, virgin surface, smooth surface&#34; or unprepared surface&#34; describe and pertain to an essentially featureless surface on a gear blank into which gear teeth are to be cold rolled. A virgin surface may be formed or machined, as by turning in a chucking machine or lathe. to a specified diameter. These terms are used to distinguish over gear blank surfaces which carry some preformed indicia or indications of desired gear tooth spacing. These terms are used to distinguish from gear blanks which have been prehobbed or the like to incorporate rudimentary teeth or tooth spacing grooves prior to commencement of the cold rolling process.  
  The term constant profile&#34; is used with reference to teeth on gear forming rolls in which each tooth on the forming roll is of constant profile along its length on the forming roll.  
  The term finished state, as used with reference to cold rolled gear teeth, means that the rolled teeth are not further formed or shaped after completion of the cold rolling process. The term finished state&#34; does contemplate that the cold rolled gear may be subjected to other fabrication processes, such as hardening or polishing, which do not intentionally or significantly affect the shape or profile of the rolled tooth.  
  The term conjugate&#34; is used with reference to the teeth on the gear forming rolls and means that the forming roll teeth are so profiled and shaped to be effective during the last stages of the cold rolling process to form gear teeth of the desired profile in the gear blank. Conjugate forming roll teeth may not exactly correspond to the profile of the inter-tooth space in the completed gear because of considerations of elasticity of the material of the gear blank and because of considerations of curvature of the forming roll. Other terms of similar import which have been used previously in this technology are reciprocal&#34; and &#34;mirror image.&#34;  
  Definitions of other terms used herein, such as soft start&#34; or idling blank, have been given above or are apparent from the following text.  
 DESCRIPTION OF THE DRAWINGS The above mentioned and other features of this invention are more fully set forth in the following detailed description of presently preferred embodiments of the invention, which description is presented with reference to the accompanying drawings, wherein:  
 FIG. 1 is a side elevation view of a soft start gear rolling tool;  
 FIG. 2 is a view taken along line 2-2 of FIG. 1;  
  FIG. 3 is an elevation view, partly in section, of apparatus for holding a gear blank in a lathe, for example, for gear rolling by the tool shown in FIG. 1;  
  FIG. 4 is a side elevation view, partially in crosssection of a centerless gear rolling machine;  
  FIG. 5 is a view, partly in section, taken along line 55 of FIG. 4;  
  FIG. 6 is a cross-section view taken along line 6-6 in FIG. 4; I  
  FIG. 7 is a side elevation view of a workpiece holder useful with the centerless gear rolling machine shown in FIG. 4;  
  FIG. 8 is a top plan view of the workpiece holder shown in FIG. 7;  
  FIG. 9 is an enlarged fragmentary plan view of a portion of the workpiece holder shown in FIG. 8;  
  FIG. 10 is an enlarged cross-sectional elevation view of a portion of the mechanism shown in FIG. 7;  
  FIG. II is a simplified schematic cross-section view of an aspect of the operation of the centerless rolling machine shown in FIG. 4;  
  FIG. 12 is a simplified schematic view of the rolling of a gear using the centerless rolling machine shown in FIG. 4; and  
  FIG. 13 is a Table of the constraints imposed upon a workpiece during operation of the centerless rolling machine in FIG. 4 in conjunction with the workpiece holder shown in FIG. 7.  
 DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS A gear rolling tool 10, shown in FIGS. I and 2, is usable in a lathe, for example, to cold roll gear teeth to appropriate configuration and profile in the smooth peripheral surface II of a cylindrical gear blank workpiece 12. The workpiece may be held in position for rolling by a holder assembly 13 which includes a male member 14 and a female member 15. The male and female members are so configured that, when they are engaged as shown in FIG. 3, they have coaxially aligned cylindrical shanks l6 and 17, respectively, adapted to be securely engaged in lathe headstock and tailstock chucks. In this manner, the holder assembly and the workpiece engaged therein may be positively driven relative to rolling tool by rotation of the headstock.  
  Male holder member I4 includes a coaxial projection 18 which extends coaxially of the holder member away from a workpiece engaging surface 19. Surface 19 preferably is disposed perpendicular to the axis of shank l6 and is defined by an enlarged circumferential boss 20 of the male holder member. The female holder member 17 has a similar enlarged circumferential boss 21 which defines a workpiece engaging surface 22 similar to surface l9. The female holder member is coaxially recessed at 23 through surface 22 to provide snug mating engagement with the end of projection 18. Projection I8 is a centering projection for workpiece 12 which preferably is formed to have a coaxial hole 24 sized to make snug mating engagement with the exterior of projection 18. A dog pin 25 projects from surface 19 in spaced parallel to projection 18 for cooperation with a hold 26 in workpiece 12. Dog pin 25 and hole 26 cooperate to transfer angular motion applied to shank 16 to workpiece l2. workpiece circumferential surface 11 is a virgin surface as defined above.  
  Cold rolling tool 10 includes an elongate solid barlike body 28 which preferably is proportioned and dimensioned to closely resemble the bar-like body of a tool holder of the type which is commonly used in machine shops to securely hold a high-speed steel or carbide cutting tool, and which is in turn usually clamped in a suitable holder assembly carried by the cross-slide of a lathe. A forming roll 29 is rotatably supported by coaxial trunions 30 in a mount portion 31 of tool 10. Forming roll 29 preferably is made ofa metal which has an intrinsic hardness and surface hardness substantially greater than the intrinsic and surface hardness of the metal defining a workpiece with which the forming roll is to be used. Trunions 30 are rotatably received in corresponding coaxially aligned holes 32 formed in respective ones of parallel legs 33 of mount 31. The end of the tool in which the forming roll is mounted is referred to herein for convenience as the front end of the tool. Legs 33 are rigidly connected adjacent the rear of the forming roll by a bridge 34 shown best in FIG. 2. Preferably the axis of the forming roll is perpendicular to and either intersects or is disposed closely adjacent to the elongate axis of body 28. Bridge 34 has a rear surface 35 which normally is spaced forwardly from the front surface 36 of a stop projection 37 extended from the forward portion of body 28.  
  The upper extents of legs 33 are interconnected by a bridge 38. An elongate resilient bendable beam portion 39 has its forward end securely connected to bridge 38 and has its rear extent securely connected to body 28 via an upwardly extending projection 40 carried by the body at its forward end. As shown best in FIGS. 1 and 2 as to tool 10, body 28, roll mount portion 31 including legs 33 and bridges 34 and 38, beam 39 and lug 40 are all integral with each other and preferably are cut or otherwise formed from a common piece of metal. In any event, beam 39 has a thickness perpendicular to its length and perpendicular to the axis of roll 29 which is substantially less than its length. In view of the secure connection of the opposite ends of the beam to bridge 38 and lug 40, the beam provides cantilever support of forming roll 29 relative to a body 28&#39;.  
  Assume that tool body 28 is engaged in a holder assembly carried by a lathe cross-slide, for example. Assume also that the forming roll is brought into engagement with the periphery 11 of gear blank workpiece 12, supported in chucks by the lathe headstock and tailstock, in response to infeed of the lathe cross-slide. The initial contact force of the forming roll withthe workpiece circumference is relatively small and has a reaction in tool 10 which results in bending of beam 39. The forming roll axis stays essentially stationary during further bending of beam 39 as further crossslide infeed occurs, until such time as bridge surface 35 engages stop surface 36 of the tool body. Thereafter. continued motion of forming roll 29 toward workpiece 12 is that motion which is determined by the cross-slide feed mechanism of the lathe. It is apparent. therefore. that beam 39, in combination with normally spaced stop surfaces 35 and 36 of the tool, constitutes a variableforce lost-motion means in the connection of roll mount 31 to tool body 28. Tool body 28 constitutes means for supporting roll mount 31, and forming roll 29 carried thereby, for relative movement into and out of forceful engagement with the periphery of a gear blank workpiece.  
  The dimensioning, i.e., length, thickness, and width of beam 39 are selected in combination with the nature of the beam material so that the initial engagement force of the forming roll with the workpiece periphery is sufficient, in view of the initial contact area provided between the periphery of the forming roll and the periphery of the workpiece, to produce inelastic deformation of the material defining the workpiece. This initial engagement force, however, is substantially less than the ultimate engagement force desired between the forming roll and the workpiece to achieve cold rolling, by plastic deformation, of gear teeth of the desired profile and depth in the workpiece.  
  For the purposes of illustration and example, the periphery 41 of forming roll 29 defines a plurality of forming teeth 42 arranged so that the forming roll resembles a spur gear. It will be understood however, that the forming roll may be configured to resemble a helical gear .or a herringbone gear for the rolling of helical or herringbone teeth in workpiece l2. Forming teeth 42 are profiled conjugate to the teeth desired to be formed in workpiece I2 by the cold rolling process. All of the forming teeth formed in the circumference of the forming roll are essentially identical. i.e.. are as identical as practically possible. and all have the same crosssectional profile or contour along their length. As shown in FIG. 3, it is preferred that the width of the forming roll be greater than the width. i.e.. axial dimen-&#39; sion, of gear blank workpiece 12.  
  It is preferred that the diameter of forming roll 29 be substantially greater than the diameter of any gear blank workpiece with which the forming roll is to be used. In this manner. upon initial engagement of the forming roll with the gear blank workpiece. the location on the workpiece periphery which is engaged by the forming roll appears to be looking at, or be engaged by, a rack.  
  Assuming that cold rolling tool is used in a lathe to roll finished gear teeth in the virgin surface of workpiece I2 held in the lathe between the headstock and tailstock as by mounting assembly 13, it is preferred that the headstock drive gearing be selected with respect to the cross-slide rate of infeed toward the workpiece so that the workpiece experiences several rotations in the period between initial engagement with the forming roll and positive engagement between tool stop surfaces 35 ad 36. In this manner the ultimate desired forceful cold rolling engagement force of the forming roll with the workpiece is progressively established over several rotations of the workpiece from the initial engagement force described above. In other words, cold rolling gear forming tool 10, shown in FIGS. 1 and 2 and described above, inherently provides the soft start feature referred to above.  
 It will be noted that forming roll 29 is passively rotatable in tool 10 and is not actively driven in the tool. Any rotation of the forming roll relative to the tool body which occurs during the use of the tool is rotation induced in the forming roll by reason of its engagement with a positively driven workpiece. Thus, tool 10 also incorporates the idling blank feature mentioned above.  
  It will be understood that rolling tool 10 may be used to advantage in a cold-rolling gear forming process only where the gear blank workpiece and its holding assembly are of sufficient size and strength to accommodate the reaction forces associated with full forceful engagement between the forming roll and the workpiece. If desired, backup rolls may cooperate with holder assembly 13; for this reason it is preferred that the outer circumferential surfaces of bosses and 21 be cylindrical surfaces as shown at 43 in FIG. 3.  
  A centerless. soft start. cold rolling, gear forming machine 45 is shown in FIGS. 4, 5, and 6. Machine 45 is particularly useful in the centerless cold rolling of finished gear teeth in the virgin surface of a pinion gear blank workpiece such as workpiece 46 shown in FIG. 9, for example. It should be understood, however, that with appropriate increases in its scantlings, the principles and features of machine 45 may be incorporated in a machine for rolling finished gear teeth in gear blank workpieces of a size like that contemplated by workpiece 12.  
  Centerless rolling machine 45 includes a base and carrier 47 for a fixed axis gear forming roll 48, and a carrier 49 for a movable axis gear forming roll 50 equal in diameter to roll 48. Carrier 49 is hingeably connected to carrier 47 by hinge shaft 51 positioned parallel to and equidistantly from the axes of rotation 52 and 53 of forming rolls 48 and 50, respectively. Movement of carrier 49 about hinge shaft 51 toward carrier 47 is controlled by a soft start drive assembly 54 coupled between carrier 49 and an arm 55 secured to base and carrier 47. Retracting movement of carrier 49 about hinge shaft 51 away from carrier 47 is controlled by adjustable return drive assembly 56. Carrier 47 is adapted to be secured to a suitable foundation 57 as by bolts 58.  
  As shown best in FIG. 6, forming rolls 48 and 50 are carried on respective drive shafts 59 and 60 adjacent the front end of carriers 47 and 49. respectively. The drive shafts are passed parallel to each other through oversized bores 61 formed in the respective carriers to extend beyond the rear faces of the carriers. Shafts 59 and 60 are rotatably supported adjacent the opposite ends of bores 61 by bearing assemblies 62, such as ball bearing assemblies.  
  Identical forming roll drive gears 63 and 64 are carried on the rear ends of shafts 59 and 60. respectively. A drag brake assembly 65, such as a disk of high friction material, is engaged between the front face of each drive gear and the stationary rear faces of bearing assemblies 62, e.g. The effective drag on each of the drive gears by the adjacent drag brake assembly is determined by the force of egagement between the gear and the drag brake assembly as set by a nut 66 engaged on the threaded rear end of the adjacent drive shaft for engagement with the rear face of the drive gear.  
  Each of the drive gears 63 and 64 is engaged with and driven by an intermediate gear 68 rotatably mounted on the rear end of hinge shaft 51 by a suitable bearing assembly 69. A drag brake assembly 70, similar to drag brake assemblies 65, is engaged between the front face of intermediate gear 68 and the rear faces of carriers 47 and 49, as shown in FIG. 5. The intermediate gear is engaged-with and driven by a drive gear 71 driven by a suitable drive motor 72 either directly or via speed reducing gears. as appropriate. In a presently preferred embodiment of centerless gear rolling machine 45, the gearing between forming rolls 48 and 50 and drive motor 72 is arranged so that the forming rolls rotate at about 60 rpm. As noted above, the axes of rotation 52 and 53 of the forming roll drive gears 63 and 64 are equidistantly spaced from the axis of rotation of intermediate gear 68. Accordingly, forming rolls 48 and 50 are rotated in the same direction at equal rates throughout motion of carrier 49 toward and away from carrier 47 during operation of motor 72.  
  A washer 73 is disposed between the rear face of each of forming rolls 48 and 50 and the inner race of forward drive shaft bearings assemblies 62, as shown in FIG. 6. The forming rolls are fixed to the front end of the respective drive shafts in a keyless manner, as by friction washers 74 and nuts 75. If a friction connection of the forming rolls to the front ends of their drive shafts is used, the torque required to produce slippage of the forming rolls about their drive shafts is substan tially greater than the torque required to overcome the drag of drag brake assemblies upon drive gears 63 and 64.  
  Drag brake assemblies 65 and are provided in association with gears 63, 64 and 68 so that, during operation of machine 45, each of these gears is always backed up against its driving gear so as to overcome backlash which is always inherent in any gear drive arrangement. As will be made apparent in the following description. the elimination of backlash from the drive gearing associated with forming rolls 48 and 50 is important in order that the forming teeth defined in the peripheries 76 and 77 of forming rolls 48 and 50, respectively, will not vary during the rolling of a single workpiece or from workpiece to workpiece once machine 45 and its workpiece holder 78 have been suitably adjusted.  
  Workpiece holder 78 is mounted to foundation 57 adjacent the front of centerless gear rolling machine 45 essentially parallel to the axes of forming rolls 48 and 50. As shown best in FIGS. 7 and 8, workpiece holder 78 includes a base 79 and a cover 80 which enclose and guide an elongage slide member 81 in reciprocal motion. Preferably the slide member is constrained by the base and cover from rotation about its elongate extent. Preferably the slide member is of rectangular crosssectional configuration to make a tight sliding fit with a correspondingly configured groove 82 formed along the length of the base and enclosed by cover 80. The holder assembly is held against foundation 57 by a pair of elongate bolts 83 which are passed through oversized apertures 84, formed vertically in the holder assembly along its opposite sides intermediate its length, and into threaded engagement with foundation 57.  
  Stop means are provided in the workpiece holder for adjustably defining the extended position of the slide member toward the centerless gear rolling machine 45. To this end a pin 85 depends from the lower rear surface of slide member 81 for cooperation with the end of a bolt 86 threaded into base 79 below the slide member. A lock nut 87 cooperates with bolt 86 for fixing bolt 86 in its adjusted position.  
  A lug 88 extends laterally from each corner of base 79 adjacent the lower surface of the base and is drilled and tapped to receive a vertically disposed adjustment screw 89, each of which has its lower end adapted for bearing against foundation 57. The oversized holes 84 for tie-down bolts 83 facilitate fine adjustment of the position of the workpiece holder assembly on foundation 57, particularly the elevation of the front end, i.e., the end of the holder assembly disposed toward machine 45. A knob 90 is secured to the rear end of slide member 81 for moving the slide member toward and away from its adjusted limiting position toward the centerless gear rolling machine.  
  As shown best in FIGS. 7 and 8, the front end of slide member 81 extends from the front of base 79 and there carries on its upper extent a workpiece receiving and retaining assembly 92. An upwardly opening recess 93, having a width less than the width of slide member 81, opens to the extreme front end 94 of the slide member and has its elongate extent centered with the elongate extent of the slide member. A workpiece receiver member 95 is held in the appropriate position member into the slide member. Preferably screw 96 is disposed adjacent the rear end of the receiver member. Screw 96 also mounts a leaf-type retainer spring 97 to the top of receiver member 95 via a shouldered washer 98 and an oversized hole 99 in the rear end of the retainer spring as shown best in FIG. 10.  
  Receiver member 95 and retainer spring 97 are defined and shaped with respect to a particular gear blank workpiece with which they are to be used. It will be understood, therefore, that receiver member 95 and retainer spring 97 as shown in FIGS. 7 through 10, for example, are defined with particular reference to pinion gear blank workpiece 46 and are shown and described for the purpose of example. It will be understood that where the gear blank workpiece has a configuration different from the configuration of workpiece 46, then the configuration and cooperation of the receiver member and retainer spring may be different from that shown in the accompanying drawings. It is because the receiver member and retainer spring are designed with respect to a particular workpiece geometry that these elements of holder 78 are removably mounted to the front end of slide member 81 by screw 96.  
  As shown best in FIG. 9, pinion gear blank workpiece 46 has a relatively large diameter elongate shank 100 on which a circumferential shoulder 101 is defined somewhat toward the rear end of the workpiece. A pair of equal diameter pinion blank cylinders 102 are closely spaced adjacent each other coaxially on the front end of a pinion shaft 103 which is connected at its rear end to the front end of shank 100 via a transistion 104, shaft 103 being of smaller diameter than shank 100. All of these elements of workpiece 46 are coaxially aligned with each other and are concentric to the axis of the workpiece. Pinion blank cylinders 102 are formed, as by turning or the like. to a predetermined diameter and their circumferential surfaces are virgin surfaces according to the definition set forth above.  
  workpiece 46 has the configuration described and shown because of its usage and function in the product in which it is used following rolling of gear teeth on pinion blank cylinders 102. That is. workpiece 46 is not configured to have the form described or shown because of any requirements of the gear rolling process.  
 Specifically, workpiece 46, when fully finished. is used to define the output gear in a one-stage motion amplifying gear train in a friction wheel distance measuring device sold in the United States under the trademark TRAl(&#34; by Southwestern Industries, Inc.. Los Angeles, Calif. Two pinion blank cylinders are defined on workpiece 46 because of certain design features of the friction wheel measuring device which are not here pertinent, but it will be understood that, if desired. a single pinion blank cylinder having a total length equal to the aggregate length of cylinders 102 could be provided in workpiece 46 if desired.  
  Receiver member and spring 97 are configured to provide the desired receiving and positioning constraints for workpiece 46 during initial positioning of the workpiece in holder assembly 78 and during cold rolling of finished gear teeth in pinion blank cylinders 102 by use of centerless rolling machine 45. Accordingly, an upwardly opening elongate recess 105 is formed in the top of the receiver member so that the recess opens to the front end 106 of the receiver member. Recess 105 is approximately as deep as the diameter of work piece shank and has a width across the width of the receiver member which is substantially greater than the diameter of workpiece shank 100 but is less than the width of the receiver member. A slot 107 is formed transversely of the entire width of the re ceiver member and has a depth into the receiver member greater than the depth of recess 105. Slot 107 is of sufficient depth that when workpiece 46 is positioned in recess as shown in H0. 9, workpiece shoulder 101 is disposed in the slot but does not contact the bottom of the slot. The slot has a width between its opposite side surfaces, i.e., those surfaces which extend transversely of the length of the receiver member 95 and of recess 105, which is somewhat greater than the extent of shoulder 101 along the length of shank 100. Recess 105 and slot 107 are so disposed in receiver member 105 that when workpiece 46 is disposed in the recess with shoulder 101 positioned in slot 107, the workpiece projects beyond the front ends of receiver member 95 and slide member 81 so that pinion blank cylinders 102 may be moved into position between the adjacent portions of gear forming rolls 48 and 50.  
  As shown best in FIG. 8, retainer spring 97. at its end opposite from screw 96, has a hammerhead-like configuration 108 defined by a pair of tabs which extend laterally in opposite directions from the body of the spring. The total transverse extent of spring 97 through the hammerhead configuration is greater than the width of retainer member recess 105. Spring 97 preferably is defined by a piece of very thin sheet metal appropriately bent as illustrated in FIG. 7 so that, when workpieces 46 is disposed in recess 105 and spring 97 has its hammerhead configuration 108 engaged with the top of the workpiece, the spring exerts only sufficient downward force on the workpiece to keep the workpiece in recess 105. A retaining force of about one or two grams is sufficient. Also, spring 97 has very low stiffness such that, during the centerless rolling of gear teeth in workpiece 46, the workpiece can move upwardly out of recess 105 without causing the bias force exerted by spring 97 on the workpiece to increase appreciably.  
  Referring again to FIG. 4, the soft start drive assembly 54 of centerless gear rolling machine 45 includes an operating knob 110 which is connected to one end of an externally threaded shank 111 received in an internally threaded hole 112 formed in arm 55 adjacent movable carrier member 49. Knob 110 and shank 111 preferably are integral and are coaxially bored along their length to define a hole which has (proceeding along the length of the bore from knob 110) a major diameter portion 113, an intermediate diameter portion 114 and a minor diameter portion 115. A pin 116 is slidably disposed in bore minor diameter portion 115 and is fixed to movable carrier 49 by a lock nut 117, the outer surface of which defines a stop surface 118 for cooperation with the adjacent end surface of shank 111. Pin 116 has an enlarged head 119 disposed in bore portion 114. A compression spring 120 is disposed in the bore intermediate portion to have one end bear against pin head 119 and to have its other end bear against a plug 121 received in the bore enlarged diameter portion. Spring 120 is still relative to the bias spring 122 of return drive assembly 56.  
  The return drive assembly includes a knurled-head adjustment bolt 123 which has its shank engaged in a tapped hole formed through a finger 124 extended from carrier 49. A lock nut 125 cooperates with the bolt shank between the bolt head and finger 124 for locking the bolt in its adjusted position relative to the finger. The bolt shank extends through finger 124 toward the opposing stop surface of a stop pad 126 carried by base 47. Spring 122 is a compression spring which is engaged circumferentially of the bolt shank between the stop pad and the adjacent surface of finger 124. Bolt 123 is adjusted in carrier 49 to provide a desired limit of travel of forming roll 50 toward forming roll 48; this limit is defined in conjunction with the depth of the forming teeth on forming rolls 48 and 50,  
 and in combination with the diameter of the gear blank to be rolled, so that, when the forming rolls are in their limiting position toward each other, gear teeth of the desired depth will have been rolled in the gear blank.  
  To use centerless gear rolling machine 45 and holder assembly 78, the holder assembly is adjusted in position relative to foundation 57 so that when a desired workpiece is received in the holder assembly and the slide member 81 is moved to its limiting position toward the rolling machine, the axis of the workpiece is essentially parallel to forming roll axes 52 and 53 and lies essentially in the plane of the forming roll axes as shown in FIG. 12. FIG. 12 is a simplified illustration which. with FIG. 11, shows the engagement of a simplified workpiece 46&#39; which has the essential characteristics of workpiece 46 (FIG. 9) but in which a single pinion blank cylinder 102&#39; is illustrated. The appropriate positional adjustment of the holder assembly on foundation 57 is facilitated by adjusting screws 89 and the tie-down bolts 83. Return drive assembly 56 is adjusted to define the desired limiting position of forming roll 50 toward forming roll 48. Slide member 81 of the workpiece holder assembly is then retracted from the centerless rolling machine and a workpiece 46 is positioned in receiver member 95. Retainer spring 97 is then engaged with the workpiece so that the workpiece cannot fall from the receiver member as the slide member comes to a stop upon being pushed forward in the holder assembly. The force of engagement of the retainer spring with the workpiece is sufficiently small that a workpiece can move laterally in recess and, within the limitations imposed by slot 107 on shoulder 101., can both rotate and move angularly in the recess. Axial movement of the workpiece in the receiver member is limited by the clearance afforded by the width of slot 107 to shoulder 101. It is assumed that when the workpiece is moved into position between the rotating forming rolls. the forming rolls are retracted from each other to provide sufficient clearance relative to the workpiece that the workpiece does not engage either forming roll.  
  in the retracted position of the soft start drive assembly, the end of shank 111 is spaced from stop surface 118. After the workpiece has been positioned between the rotating forming rolls, knob is turned to cause shank 111 to be advanced in hole 112 toward carrier 49. Such operation produces compression of spring 120, which compression forces are greater than the return bias forces associated with spring 122, so that carrier 49 rotated about hinge shaft 51 to cause forming roll 50 to move toward forming roll 48. The compression forces developed by spring are sufficient that, when forming the rolls move sufficiently toward each other to cause the initial contact of the workpiece with both of the forming rolls, the force of engagement of the forming rolls with the workpiece is substantially less than the ultimate cold rolling force desired in the gear forming process. The initial contact force is sufficient, in connection with the total contact area of the forming rolls with the virgin surface of the workpiece, to cause inelastic deformation of the workpiece material so that a faint trace of the forming teeth is impressed in the circumference of the workpiece gear blank cylinder. Obviously, as the workpiece is first engaged with either of the forming rolls it tends to be rotated by the roll and also to be brought into a position between the forming rolls which is determined not by the holder assembly but by the geometry of the forming rolls and of the workpiece and by the forces applied to the workpiece by the forming rolls. Preferably, initial engagement of the workpiece by the forming rolls produces a slight lifting of the workpiece out of engagement with recess 105 but not out of engagement with slot 107. Continued operation of knob 110 produces further compression of spring 120 until such time as shank lll moves into physical contact with stop surface 118. During this interval, the force of engagement of the forming rolls with the workpiece is determined by compression forces developed in spring 120. On the other hand. once shank 111 has physically engaged stop surface 118, the force of engagement of the forming rolls with the workpiece is dependent upon the position of shank 111 in arm 55. Knob 110 is turned further to drive the forming rolls to their limiting position toward each other as defined by return drive assembly 56 and its adjustment. When the forming rolls reach their limiting position toward each other, gear teeth of the desired profile and depth will have been cold rolled from a virgin surface into the workpiece. Knob 110 is then turned in the opposite direction to produce retraction of forming roll 50 sufficient to free the workpiece from the forming rolls. Holder assembly slide member 81 is then retracted and the workpiece, with the desired gear teeth fully cold rolled in pinion blank cylinders 102, is then removed from the holder assembly and a new workpiece inserted in its place for rolling of gear teeth thereon.  
  As an example, the rolled pinion gears used in the aforementioned friction wheel measuring device have ten helical teeth rolled in the circumference of pinion blank cylinders 102. The helix angle of these teeth is Prior to the commencement of the rolling process the pinion blank cylinders have an outer diameter of 0.0549 inches. In the centerless gear rolling machine in which these pinion gears are rolled, forming rolls 48 and 50 are 2 inches in diameter and have a rotational rate of about 60 rpm.  
  It is important in the rolling of gears by the use of centerless gear rolling machine 45 and holder assembly 78, that the holder assembly impose no constraints on the movement of the workpiece which are redundant to constraints imposed by the forming rolls as and after the gear tooth track is established in the workpiece by the forming rolls. The holder assembly should be arranged to receive and support a workpiece so that the workpiece may move in the holder assembly in a desired manner after first being contacted by either one of the forming rolls, so that it can move in response to continued movement of the forming rolls toward each other into contact with both of the forming rolls, and so that, when engaged by both forming rolls, it can assume a position determined principally by the forming rolls themselves and the relationship of the forming teeth on the two forming rolls.  
  The presence of the drag brakes in the gearing of machine 45 keeps the gears backed up against their driving gears at all times during the gear rolling process. The lack of this characteristic would allow the workpiece to pop up or down from its initial position between the forming rolls if that initial position were precisely on a line between the centers of the forming rolls and the forming rolls were forcefully applied against the workpiece at the time of initial contact. It is preferred that the holder assembly 78 be so adjusted relative to rolling machine 45 that the workpiece is located slightly above (about 0.0002 of an inch or so) the line between the forming roll centers so that. if there is a tendency of the workpiece to pop out of its initial point of engagement between the forming rolls, the workpiece would pop upwardly away from receiver member to pop downwardly from its position of initial contact between the forming rolls, the workpiece would move against the structure of the holder assembly, which event would generate constraints upon the workpiece redundant to the constraints imposed upon the workpiece by the forming rolls. Also, it is desirable that the forming rolls be of large diameter relative to the diameter of the workpiece to minimize, to the greatest extent possible. eccentric forces applied to the workpiece. ln other words, it is desirable that the forming rolls be sufficiently greater in diameter than the gear blank portion of the workpiece that the workpiece. as engaged with the forming rolls, appears to be contacted by a rack. 7  
  in the practice of the idling blank or centerless rolling features of this invention, the first several rotations of the gear blank. after having been contacted by all forming rolls, are of particular significance. It is during these first several rotations that the basic spacing of the teeth to be formed in the blank are defined by the forming rolls. The initial definition of the spacing should be very slight, i.e., the initial contact of the forming rolls with the gear blank should be sufficiently forceful to produce inelastic deformation of the workpiece material such that impressions of the forming rool teeth are left in the periphery of the gear blank. These impressions, however, should be very shallow and sufficient in depth only to permit forming rolls 48 and 50 to begin to rotate the workpiece without slippage and to permit the forming rolls to move the workpiece into a satisfactory position between the forming rolls. The first one or two revolutions of the workpiece after being engaged by both forming rolls is particularly important. If the trace of forming teeth impressions on the workpiece -defined by one of the forming rolls does not register exactly with the trace defined on the workpiece by the forming teeth of the other forming roll, then this deviation between the two sets of traces can be eliminated during the next several rotations of the workpiece if (1) the workpiece is properly positioned relative to the forming rolls at the time the workpiece is first engaged by both forming rolls, and (2) the force of engagement of the forming rolls with the workpiece increases gradually to the full cold rolling force level. If these criteria are not observed, then either the wrong number of teeth will be rolled in the workpiece or the teeth rolled in the workpiece will be badly mutilated and totally unacceptable. lf these criteria are observed, the correct number of teeth of the desired profile and depth will be rolled in the workpiece. ln this respect, the diameter of the gear blank determines the basic number of teeth to be rolled in the workpiece, assuming that the height of holder assembly receiving member 95 is initially set consistent with the relative positioning of the forming teeth on the two forming rolls.  
  Assume that an even number of teeth are to be rolled in workpiece 46 by use of centerless rolling machine 45. in this case, the height of receiver member 95 above foundation 57 should be adjusted so that when the workpiece is first contacted by both forming rolls, a line through the workpiece between the point of contact with a forming tooth on roll 48 to the point of contact by the first forming tooth on roll 50 passes through the axis of the workpiece. In other words, the points of Contact with the workpiece by the first two forming teeth to engage the workpiece, one forming tooth being defined by roll 48 and the other by roll 50, should be at diametrically opposed locations on the workpiece. If this situation is produced. then the first impression made by forming roll 48 on the workpiece will exactly register with forming teeth on roll 50. and vice versa, after the workpiece has rotated 180 in response to being engaged between the two positively driven forming rolls.  
  lf an uneven number of teeth are to be rolled in the workpiece, then the holder assembly should be adjusted on foundation 57 so that receiver member 95 is at such a height that when the workpiece is first contacted by both forming rolls, the initially contacting forming tooth on one forming roll is centered diametrically through the workpiece with the midpoint of the space between adjacent forming teeth on the other forming roll. ln this manner. the initial impressions made by one forming roll on the workpiece will register with the forming teeth on the other forming roll after the workpiece has been rotated 180 following its initial contact by both of the forming rolls.  
  Proper alignment of the forming roll teeth with each other to produce, as desired, either even or odd numbers of teeth on the workpiece may be achieved by adjusting one of the forming rolls angularly on its drive shaft relative to the other forming roll. Such adjustment procedures. however. are extremely difficult and time consuming to make. It has been found to be much simplier to vertically adjust the position of receiver member 95 relative to forming roll axes 52 and 53 to produce the desired adjustment between the points of contact of the opposite forming roll teeth with the workpiece.  
  As noted above, if the position of holder assembly receiver member 95 is appropriately adjusted relative to forming roll axes 52 and 53, the principal factor which determines a number of teeth to be formed in the workpiece is the diameter of the workpiece at its gear blank cylinder. lf the height of the receiver member relative to the forming roll axes is out of adjustment by precisely A tooth space, then the number of teeth generated in the workpiece by the cold rolling process will be twice the number of teeth actually desired and the generated teeth will have one-half the desired tooth height if, in fact, the generated teeth are recognizeable. A change by A tooth space in the height of receiver member 95 relative to the forming roll axes is equivalent to a change in the angular position of one forming roll relative to the other by /2 tooth space.  
  The foregoing examples of the positioning of the holder member relative to the forming roll axes for the rolling of even and odd numbers of teeth in the workpiece illustrate the opposite limiting conditions of adjustment of the holder assembly. For any condition of adjustment between these two limiting conditions, the rolling machine is undecided and may roll the desired number of teeth on one workpiece and may roll twice the number of teeth desired on the next workpiece, all other things being equal, especially where the adjustment of the receiver member is off by /a tooth space. The extent to which the cold rolling machine is, in effect, undecided as to the number of teeth it will roll in a workpiece depends upon the extent to which the adjustment of the receiver member height is in error. An error in receiver member adjustment from perfect adjustment. but different from an error equal to tooth space. will result in the rolling of the correct number of teeth of the correct profile and depth on the workpiece because the forming teeth on the two forming rolls will seek a common track of the correct number of impressions on the workpiece; this correction will occur if the workpiece is free to adjust itself relative to the forming rolls and if the force of engagement of the forming rolls with the workpiece increases progressively to the full cold rolling force.  
  By contrast, if one were to use a driven. centered gear blank, then one would have less worry about the details of track generation in the workpiece, and gradual application of the rolling force to the workpiece would not be so significant. In this case, however, everything has to be perfect, namely, the geometry of the machinery, the angular velocities of the forming rolls and the workpiece. the diameter of the gear blank, and the positioning of the forming teeth on one forming roll relative to the forming teeth on the other forming roll. On the other hand. when one uses the centerless idling blank technique described above, one has the advantage of accommodation of error, but it is necessary to gradually apply the cold rolling force to the workpiece, i.e., to use the soft start feature of this invention, if one is to achieve predictable and acceptable results.  
  The above described feature of accommodation of error in the precise adjustment of holder assembly 78 relative to forming roll axes 52 and 53 is achieved where the holder assembly does not impose movement constraints on the workpiece, following contact of the workpiece by both forming rolls, which are redundant to the movement constraints imposed by the forming rolls on the workpiece. ln FIGS. 7, 8 and 9, Cartesian reference coordinates X, Y and Z are illustrated. These same coordinates are illustrated in FIGS. ll and 12 which constitute simplified schematic representations of the manner in which workpiece 46 (simplified in FIGS. 11 and 12 relative to FIG. 9) is ideally engaged during the cold rolling process by the holder assembly and by the forming rolls. According to the convention adopted in the accompanying drawings, movement of the workpiece in the X direction is movement of the workpiece along its axis parallel to the axes of rotation of the forming rolls. Movement of the workpiece in a Y direction is translation of a workpiece in a plane parallel to the plane of the forming roll axes. Movement of the workpiece in a Z direction is translation of the workpiece in a plane perpendicular to the plane of the forming roll axes and parallel to the forming roll axes. The other modes of movement which the workpiece may experience are angular movements of the workpiece about the same axes.  
  The table shown in FIG. 13 lists the preferred sources of constraint on the workpiece in the six modes of movement possible. Preferably the constraints shown in FIG. 13 are the only constraints imposed on the workpiece as and after the trace of the forming roll forming teeth is generated in the workpiece. Accordingly, the workpiece is constrained from movement along its axis in an X direction by engagement of workpiece shoulder 101 in slot 107 of receiver member 95. This constraint on workpiece movement is particularly desirable where helical teeth are to be formed in a gear;  
 without such constraint the workpieces would tend to migrate along its axis out of engagement between the forming rolls during the cold rolling. gear tooth forming process. The receiver member imposes no other constraint upon movement of the workpiece such that the workpiece can move laterally in a Y direction in the holder assembly and can move upwardly in a Z direction out of the receiver member recess; downward movement of the workpiece toward the receiver member is not likely to occur where. as preferred. the workpiece is disposed slightly above the plane of the forming roll axes at the time it is initially contacted by both of the forming rolls. It will also be observed that neither the receiver member nor retainer spring 97 impose any significant constraints upon any angular modes of movement of the workpiece. Forming rolls 48 and 50 per se constrain the workpiece from linear movement in a Y direction of from angular movement in a Z direction as and after the trace of forming teeth impressions are made in the workpiece. The forming teeth themselves constrain the workpiece from movement linearly in a Z direction or angularly in a Y direction. The only remaining mode of movement possible for the workpiece is angular motion about the X axis; there is no constraint imposed in this mode since angular motion of the workpiece about an X axis is in fact rotation of the workpiece about its own axis. which rotation obviously is desired. Redundancy in constraints imposed upon the workpiece linearly along or angularly about the Y and Z axes impairs the ability of the workpiece to adjust itself following contact by both of the forming rolls to any errors in the adjustment of receiver member 95 relative to the forming roll axes. Once the tooth spacing track is established in the periphery of the gear blank cylinders of the workpiece. retainer spring 97 exerts insufficient force on the workpiece to restrain the workpiece from linear movement in a Z direction or from angular movement about the Y axis.  
  In the exemplary pinion gear described above. the teeth cold rolled to a finished state in the virgin surface of the workpiece have a 30 pressure angle. The only fabrication process to which these cold rolled pinion gears are subjected after the cold rolling process is a hardening process in which the tooth-form cold-formed into the workpiece is not deliberately or appreciably altered. Hardening of the cold rolled gears is done to improve the wear life of the gear in the product of which the pinion gears are components. Also. the gears with which these cold-formed pinion gears are meshed in the ultimate product are cold rolled in a continuous process from a virgin surface by use of rolling tool secured to the cross-slide ofa lathe. and the only fabrication process to which these gears are subjected following cold rolling is a hardening process. It is within the scope of this invention, however, that. if desired following the hardening process. the cold rolled gear teeth may be polished merely to improve the surface finish of the teeth. as opposed to changing or modifying the cross-sectional contour of the teeth.  
  So far as can be determined at this time. there is no metal presently available commercially which is sufficiently malleable to permit the rolling of 20 pressure angle tooth forms from a virgin blank to a finished state in one cold rolling process. Improvements in alloys and metallurgy are continually being realized, and the commercial availability of a metal of sufficient malleability and hardenability to permit such cold rolling of 20 pressure angle teeth for power transmission gears may be available in the very near future.  
 Workers skilled in the art to which this invention pertains will readily appreciate that the apparatus and procedures described above may be used to roll any tooth form desired in a cylindrical gear blank surface and not merely the helical or spur gear tooth forms mentioned specifically above. Also. the apparatus and procedures described above may be used to roll bevel gears. tapered gears or internal gears. if desired. Subject to the properties of the metals used to define the gear blank. this invention may be used to cold roll. in a single continuous process from a virgin surface. finished gears for power transmission or motion transmission gears if the generated tooth forms have pressure angles consistent with the characteristics of the blank metal.  
  In view of the foregoing description. workers skilled in the art to which this invention pertains will appreciate that the soft start feature described above is vital and must be used where a single forming die is used in accordance with the idling blank feature of this invention. The soft start feature. for the reasons set forth above, is also significant but not vital where centerless gear rolling techniques are used.  
  Persons skilled in the art to which this invention pertains will readily appreciate that variations or modifications may be made in the procedures and structures described above without departing from the scope of this invention. In the preceding description. certain presently preferred structures and procedures have been described for the purposes of example and illustration rather than as an exhaustive catalog of all forms which this invention may take. Accordingly. the preceding description should not be considered as limiting the scope of this invention. except in those instances where certain critical and necessary relationships or structural features have been expressly set forth.  
 What is claimed is:  
  1. In the cold rolling of finished gear teeth in a virgin surface of a rotatable metal gear blank by forceful engagement of the virgin surface by the circumference of an appropriately arranged and profiled rotatable forming roll. the improvement comprising establishing the desired tooth forming engagement of the roll with the blank progressively over several rotations of the blank from an initial engagement force sufficient in view of the initial contact area to produce inelastic deformation of the blank material but of magnitude substantially less than the desired engagement force.  
  2. The method of claim 1 wherein the initial engagement force is sufficient in magnitude to produce in the virgin surface of the blank only a trace of the forming roll circumferential contour.  
  3. The method of claim 1 including positively driving only one of the blank and the forming roll during said establishing step.  
  4. The method of claim 3 wherein said initial engagement force is sufficient in magnitude to cause the other of the blank and the forming roll to rotate without slippage relative to the one of the blank and the forming roll in response to said initial engagement.  
  5. Apparatus for cold rolling gear teeth into a smooth work surface of a rotatable metal gear blank by forceful engagement of the work surface with the appropriately arranged and profiled circumference of a rotatable forming roll, the apparatus comprising separate means for rotatably mounting a blank and a forming roll.  
 means supporting the mounting means for relative movement into and out of said forceful engagement of a blank and a forming roll engaged in the mounting means. and variable-force lost-motion means operatively associated with one of the mounting means and effective substantially in the direction of said relative movement for causing said&#39;forceful engagement to be established progressively during operation of the relative movement means following initial engagement between the blank and the forming roll.  
  6. Apparatus according to claim wherein the supporting means and the lost-motion means are cooperatively related to establish the said forceful engagement during several rotations of the blank following the initial engagement.  
  7. Apparatus according to claim 5 wherein the lostmotion means is so arranged that the force between the roll and the blank substantially upon the initial engagement is sufficient in magnitude to produce inelastic deformation of the blank work surface.  
  8. Apparatus according to claim 7 including means associated with only a first one of the mounting means for rotating the one of the blank and the forming roll engageable therein during operation of the supporting means to produce the relative movement and during engagement of the blank and the forming roll.  
  9. Apparatus according to claim 8 wherein the one of the blank and the roll engageable in the second mounting means rotates in response to said initial engagement. and the lost-motion means has a lost-motion accomodation capacity sufficient that the desired forceful engagement is established over plural rotations of the blank following the initial engagement.  
  10. Apparatus according to claim 8 wherein the first one mounting means is for rotatably mounting the blank.  
  11. Apparatus according to claim 8 wherein the first one mounting means is for rotatably mounting the forming roll. and the lost-motion means is operable for producing the relative movement between the mounting means.  
  12. Apparatus according to claim 11 including a second roll and mounting means therefor disposed in cooperation with the first one mounting means and the mounting means for the blank for engaging the blank essentially diametrically of the blank between the forming roll and the second roll.  
  13. Apparatus according to claim 12 wherein the second roll is a forming roll circumferentially profiled in cooperation with the first forming roll, and means associated with the mounting means for the second forming roll for rotating the second roll at a predetermined rate relative to the rotational rate of the first roll.  
  14. Apparatus according to claim 13 wherein the mounting means for the first and second rolls define definite axes of rotation of the respective rolls, and wherein the mounting means for the blank is defined to receive the blank for centerless rotation relative thereto.  
  15. Apparatus according to claim 14 wherein the blank mounting means is arranged to impose upon the blank during engagement of the blank between the rolls no significant constraint upon motion of the blank redundant to motion constraints imposed upon the blank by the rolls during engagement of the blank between the rolls.  
  16. Apparatus according to claim 5 wherein the apparatus is for cold rolling finished gear teeth in the blank work surface, and the forming roll circumference defines a plurality of forming teeth having constant profile conjugate to the teeth to be rolled in the blank.  
  17. Apparatus according to claim 16 wherein the forming teeth are profiled to define teeth in the blank having a pressure angle of at least substantially 28.  
  18. A tool for cold rolling gear teeth in a metal gear blank comprising a forming roll of selected circumferential contour. a carrier for the roll including a first part rotatably mounting the roll therein and a second part adapted to be engaged in ad supported by a tool holder and the like. and coupling means mounting the carrier first and second parts for movement of the forming roll substantially perpendicularly of its axis of rotation toward and away from a positive stop. the coupling means including means resiliently biasing the carrier first part to a normal position spaced from the stop.  
  19. A tool according to claim 18 wherein the first part mounts the roll for rotation about an axis fixed relative to the first part but movable relative to the second part.  
  20. A tool according to claim 19 wherein the coupling means is arranged for limiting movement of the axis to translation.  
  21. A tool for cold rolling gear teeth in a metal gear blank comprising a forming roll of selected circumferential contour. a carrier for the roll including a first part mounting the roll therein for rotation about an axis fixed relative to the first part and a second part adapted to be engaged in and supported by a tool holder and the like. and coupling means mounting the carrier first and second parts for translatory movement of the forming roll substantially perpendicularly of its axis of rotation toward and away from a positive stop. the coupling means including a beam spring coupled between the carrier first and second parts for resiliently biasing the carrier first part to a normal position spaced from the stop.  
  22. In the cold rolling of gear teeth in a smooth surface of a rotatable metal gear blank by forceful engagement of the surface by the circumference of an appropriately arranged and profiled rotatable forming roll, the improvement comprising positively driving only one of the gear blank and the forming roll during said engagement. and developing the forceful engagement progressively over several rotations of the blank.  
  23. The method of claim 22 including providing the forming roll of sufficiently great diameter relative to the blank that the portion of the blank work surface initially engaged by the roll appears to be engaged by substantially a rack.  
  24. In the cold rolling of fully finished gear teeth in a smooth work surface of a rotatable metal gear blank by forceful engagement of the blank work surface with forming teeth defined by a forming member, the improvement comprising defining the forming teeth of such profile relative to the geometry of the blank to generate in the blank fully finished gear teeth having a pressure angle of at least substantially 28.  
  25. The method of claim 24 including defining the forming teeth to be of constant profile.  
  26. Apparatus for cold rolling finished gear teeth into a smooth work surface of a metal gear blank comprising means for rotatably mounting a forming roll having a circumference arranged and profile in combination with the geometry of the blank to form in the blank work surface gear teeth of predetermined profile when the roll is circumferentially forcefully engaged with the blank work surface. means for mounting a gear blank for engagement of the work surface thereof by the forming roll. means operable for relatively moving the roll and the blank mounting means to produce engagement of the circumference of a roll engaged in the mounting means therefor with the work surface of a blank engaged in the mounting means therefor. means coupled to one of said mounting means for rotating the one of the forming roll or gear blank engaged therein during operation of the relative movement means and during said engagement, and means coupled to only one of the mounting means responsive to said engagement for progressively producing full forceful engagement of the roll with the blank.  
  27. Apparatus for cold rolling finished gear teeth into a smooth peripheral surface of a metal gear blank comprising a plurality of essentially identical forming rolls each defining in the periphery thereof a plurality of forming teeth conjugate to teeth to be cold rolled in the blank. the forming teeth being of constant profile along their length. means mounting the forming rolls for rotation about axes fixed by the mounting means, means supporting the roll mounting means for relative movement therebetween so that the rolls are movable into and out of engagement with the pheripheral surface of a blank disposed between the rolls. power means for rotating the rolls about their axes at equal velocities during movement of the rolls into and out of engagement with the blank, and means for receiving and supporting a blank between the rolls for centerless rotation relative to the receiving and supporting means in response to engagement of the blank by the rolls.  
  28. Apparatus according to claim 27 wherein the forming teeth are profiled to cold roll in the blank gear teeth having a pressure angle of at least substantially 28.  
  29. Apparatus according to claim 27 wherein the blank receiving and supporting means is arranged to impose upon the blank during engagement thereof by the rolls no significant constraint upon motion of the blank which is redundant to motion constraints imposed upon the blank by the rolls during said engagement.  
  30. Apparatus according to claim 27 wherein the forming rolls are mounted for rotation about parallel axes disposed substantially symmetrically about the received and supported position of the blank.  
  31. Apparatus according to claim 30 wherein there are two forming rolls.  
  32. Apparatus according to claim 31 wherein the blank receiving and supporting means is arranged to support the blank substantially in a plane common to the roll axes upon engagement of the rolls with the blank.  
  33. Apparatus according to claim 32 wherein the blank receiving and supporting means includes means for adjusting the supported position of the blank normally of the plane of the roll axes upon engagement of the rolls with the blank.  
  34. Apparatus according to claim 33 wherein the plane of the roll axes is horizontal and the supported position of the blank is slightly above the plane.  
  35. Apparatus according to claim 31 wherein the means supporting the roll mounting means include a hinge connection between the roll mounting means. the hinge axis being equidistant from the two roll axes.  
  36. Apparatus according to claim 27 including means coupled to the roll mounting means for moving the rolls into forceful engagement with a blank disposed therebetween and including means for establishing said forceful engagement progressively over several rotations of the blank following initial engagement of all of the rolls with the blank.  
  37. Apparatus according to claim 36 wherein the force establishing means includes variable-force lostmotion means defined to cause the rolls substantially on said initial engagement with the blank to apply to the blank a force which, in cooperation with the initial contact area of the rolls with the blank, is sufficient to produce inelastic deformation of the blank peripheral UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3, 77,273  
 DATED April 15, 1975 mvrrrrokrgg I IRVEN H. CULVER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
  Column 2, line 29, change &#34;users&#34; to uses Column 7, line 27, change &#34;ad&#34; to and Column 8, line 26, &#34;egagement&#34; should read engagement Column 9, line 14, &#34;elongage&#34; should read elongate column 9, line 56, after &#34;position&#34; insert in recess 93 by a screw 96 which passes through the receiver Column 10, line 2, after &#34;understood,&#34; insert therefore, that receiver member 95 and retainer spring 97 as shown in FIGS. 7 through 10, for example are defined with particular reference to pinion gear blank workpiece 46 and are shown and described for the purpose of example. Column 11, line 20, &#34;workpieces&#34; should read workpiece column 11, line 51, &#34;still&#34; should read stiff Column 12, line 51, &#34;rotated&#34; should read rotates Column 14, line 31, &#34;rool&#34; should read roll Column 20, line 13, &#34;ad&#34; should read and En&#39;gned and Scaled this twenty-third Day of September 1975 [SEAL] A nest:  
 .RUTH C. M A SON C. MARSHALL DANN t-lrtcxlrng ()fjr&#39;ur (mnmrlm&#39;r&#39;mrcr nflalcnrs and Trademarks