Patent Publication Number: US-6213838-B1

Title: Metal yo-yo and method for manufacture

Description:
FIELD OF THE INVENTION 
     This invention relates to yo-yos and particularly to yo-yos fabricated from metal. 
     BACKGROUND OF THE INVENTION 
     Yo-yos most commonly are made from wood or from a molded plastic as the principal material of construction. Yo-yos made from different materials present a different feel to the yo-yo player, some players preferring the feel of one over the other. Some yo-yos have been made from metal which presents still another feel that may be preferred by some players. Few metal yo-yos have been commercialized, however, and, as to those, their availability has been limited possibly because the typical construction for such yo-yos is costly and is substantially more than that of a more conventional yo-yo made from plastic or wood. In one prior art construction, the metal yo-yo may be formed from aluminum by machining the yo-yo halves that will be assembled to form the yo-yo body in a milling machine from solid round aluminum bar stock. The entire yo-yo half is formed, in one piece, from the round aluminum bar stock. The end of the bar stock is milled to form the outer face of the yo-yo half by removing an annular region of material, leaving a center hub and a peripheral rim. The peripheral contour of the yo-yo half also may be milled, as may be the inner face of the yo-yo half. The milled piece then is cut-off from the round bar stock to a thickness appropriate for the yo-yo half. The inner face of the yo-yo half then is machined further by drilling and tapping a center hole along the central axis of the yo-yo half to accept the threaded end of an axle by which two yo-yo halves will be joined. After machining, the yo-yo halves then are individually polished and finished. Such one-piece yo-yo halves are made individually in a labor intensive process that is wasteful of material, all of which adds to the cost of the yo-yo. 
     Also among the desirable features of a yo-yo, especially for those users who wish to perform complex string tricks, is to provide a wide peripheral entry to the string slot between the yo-yo halves. Yo-yos having such a wide entry sometimes are referred to as having a “butterfly” configuration. While incorporating a butterfly configuration in a plastic injection molded yo-yo is simply a matter of configuring the mold for the yo-yo halves, the fabrication of a butterfly yo-yo from metal, using the prior art milling technique described above, presents additional difficulties in milling the peripheral surfaces as well as the inner surfaces of the yo-yo halves. Such milling results in still further waste of material and additional labor and other expenses attendant to finishing the surfaces of the yo-yo halves. The milled one-piece metal yo-yo involves a machining process that can be expected to leave marks and other irregular surface regions that should be finished to a smoother surface in order to accept a desired finish, such as anodizing or finishing graphics. The milled metal yo-yo halves do not lend themselves to mass finishing but, instead, must be finished individually, adding further to the cost of the yo-yo. 
     It would be desirable to provide a metal yo-yo embodying a construction and method of manufacture that would reduce substantially the cost and ease of manufacture while providing a metal yo-yo with desirable characteristics, including the ability to form a butterfly yo-yo. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, each yo-yo half is made in two pieces, including a die cut, stamped body and a central hub attached to the body, both components being formed from a suitable metal. The body is made by die cutting an annular disc from a flat sheet of metal, the disc having a central hole adapted to receive the hub. A plurality of such discs can be die cut simultaneously from a larger sheet. Each flat disc then is subjected to a drawing process in which the disc is deformed about its periphery to form a flared rim that, in an assembled yo-yo, may cooperate with another such disc to define a wide butterfly entry to the string slot. A plurality of the drawn discs can be polished together in a mass polishing machine together with a suitable polishing grit. After polishing, the central hub is attached to the drawn disc. The hub is configured to facilitate its assembly with a drawn disc by fitting it into the central hole in the disc and then deforming some of the metal of the disc to constrict securely about the hub. The hub is designed for mass production on conventional equipment. The inwardly facing side of the hub is provided with a threaded bore adapted to receive a threaded end of the yo-yo axle. The yo-yo halves then are assembled by attaching them to the threaded ends of an axle that may include additional axle assembly components, such as bearings, bearing surfaces or the like. 
     Among the objects of the invention are to provide a metal yo-yo and method for its manufacture that results in substantial economies; to provide a metal yo-yo in which each yo-yo half is formed from a separately formed disc and hub; to provide a metal yo-yo having a butterfly configuration; to provide a metal yo-yo in which the machining and finishing operations are minimized; and to provide a metal yo-yo construction in which the components of the yo-yo can be processed in batches and to provide a process for manufacturing such a yo-yo. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof, with reference to the accompanying drawings wherein: 
     FIG. 1 is a diagrammatic illustration, in quarter section, of a prior art metal yo-yo in which the halves have a one-piece machined construction; 
     FIG. 2 is an illustration similar to FIG. 1, of a yo-yo made in accordance with the invention; 
     FIG. 3 is an illustration of a single flat disc that has been die cut from a sheet of metal; 
     FIG. 4 is an illustration of a disc that has been stamped to deform it to a peripherally flared configuration; 
     FIG. 5 is an enlarged quarter section illustration of the hub; 
     FIG. 6 is an illustration of the inner end of the hub as seen from the right of FIG. 5; 
     FIG. 7 is an illustration of the inner face of an assembled yo-yo half after the inner surface of the disc has been swaged; 
     FIG. 8 is a sectional illustration of the region of the swaging as seen along the line  8 — 8  in FIG. 7; 
     FIG. 9 is an enlarged full section illustration of the assembled yo-yo; and 
     FIG. 10 is a further enlarged sectional illustration of a connection between the hub and the disc of a yo-yo half. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a metal yo-yo having a prior art construction in which each of the yo-yo halves  10 ,  12  is machined in one piece from metal bar stock. Each yo-yo half  10 ,  12  may be formed on a milling machine that exposes an end of round bar stock, for example, of aircraft grade aluminum. The outer end face of the bar stock is milled to remove a substantial amount of material leaving an annular region  14  that encompasses and defines a hub  16  and a peripheral rim  18 , connected by a web  20 . 
     The outer peripheral surface  22  of the rim also may be machined to a desired contour. The inner face  24  of each yo-yo half may be formed so that when mated with an identical yo-yo half, the inner faces  24  will define a string slot  26  as desired, for example, with the more radially inwardly disposed regions of the slot defining a narrower space than the more outwardly disposed regions. A hole  28  then is drilled and tapped at the inner face  24  of each yo-yo half. The threaded hole is adapted to receive the threaded end of an axle  30  by which the two yo-yo halves  10 ,  12  may be secured together. The axle hole  28  extends into the outwardly projecting hub  16  of the yo-yo half. The axle  30  may be part of an assembly that includes an appropriate bearing arrangement, indicated generally at  32  and may be a ball bearing or a bearing arrangement as that described in U.S. Pat. No. 4,895,547, the disclosure of which is incorporated by reference herein, in its entirety. Before assembly, a number of processes may be performed to enhance the appearance of the yo-yo, such as polishing, painting, graphic finishing, anodizing or the like. Where the yo-yo halve is machined from a single piece of material, as in the prior art described above, it does not lend itself to batch treatment with other yo-yo halves and can be expected to require individual finishing and fabrication. That, coupled with the expense of machining individual yo-yo halves, including the waste of material, results ultimately in a yo-yo that necessarily is very costly as compared to a yo-yo made from more conventional materials (e.g., plastic). 
     FIG. 2 illustrates a metal yo-yo embodying the invention. The yo-yo includes yo-yo halves  34 ,  36 . The axle  30  and bearing arrangement  32  may be similar to or the same as that used in the embodiment of FIG. 1, a ball bearing being preferred. The yo-yo halves  34 ,  36 , however, are fabricated from two components, a disc  38  and a hub  40 , that are formed separately and then are combined and secured together to form the finished yo-yo half. The construction of the yo-yo half and its process for manufacture enables such yo-yos to be fabricated economically with a resultant cost substantially less than that of the type of yo-yo shown in FIG.  1 . 
     FIG. 3 illustrates a disc  38  in its flat configuration after it has been cut, as by die cutting, from a flat sheet of material, preferably aluminum. A plurality of such discs can be die cut simultaneously from a flat sheet or strip of aluminum in a single die cut procedure. By way of example, an aluminum sheet 0.125 inch thick formed from an alloy that lends itself to being die cut and deformed (e.g., No. 3003-1114) may be cut to define discs with an outer diameter of 2.25 inches and having a center hole  42  about 0.50 inch in diameter. The sharp corners defined at the die break preferably are rounded slightly by machining or by using a progressive die cutting tool to coin the die break. 
     FIG. 4 illustrates the disc  38  after it has been stamped in stamping dies (not shown) to deform the outer peripheral margin  44  of the disc to flare outwardly, defining somewhat of a dished shape. The disc  38 , having been formed from a uniform thickness sheet, thus can be stamped to simultaneously define the shape and contour of the inner and outer faces  46 ,  48  of the yo-yo half. The contour of the stamping dies may be selected to control the configuration of the string slot  50  (FIG.2) and may be formed to include a substantial flare by which a butterfly-configured yo-yo will be formed when the yo-yo is assembled. Thus, the contour of the outer and inner faces  46 ,  48  can be formed simultaneously in a simple inexpensive operation in which there is minimal waste of material. Additionally, by embodying the foregoing construction and process, after the discs have been stamped, they may be polished in a batch (e.g., several hundred at a time) as by tumbling with an appropriate polishing grit to prepare the surface for further finishing, as desired. Where the disc is formed to its desired contour by bending, without machining, it does not have the machining marks that result from the prior art milling process and may be considered as already in a semi-finished state even before polishing. 
     FIGS. 5 and 6 illustrate the preferred embodiment of a hub adapted for secure connection to the formed disc to complete the structure of the yo-yo half. The hub, indicated generally at  40 , may be formed from an aluminum alloy that lends itself to fabrication in an automatic screw machine, No. 2011 aluminum, being preferred. Such hubs  40  can be produced inexpensively and in substantial quantities, as on a Davenport multi-spindle automatic screw machine. The hub  40  includes an outer end  54  that will project outwardly into the dished region defined by the outer face  48  of the disc  38  after the parts are assembled. The hub  40  has an inwardly facing annular margin  56  with a diameter greater than that of the center hole  42  in the disc. When the hub  40  is assembled with a disc, the margin  56  of the hub  40  will bear firmly against the outer face  48  of the disc  38  in the marginal region about the center hole  42 . The inner end of the hub is formed to include a projection  58  adapted to be closely fitted into the center hole  42  of the disc  38 . The projection  58  is formed to include a locking band  60  having an outer peripheral surface  61  defined by a knurled pattern (e.g., a straight knurl of 128 diametral pitch) that can be fitted into the center hole  42  of the disc  38 . The outer diameter of the locking band  60  is closely fitted to the diameter of the center hole  42  so that the two parts can be mated with relatively light force. So mated, the hub and disc, in the preferred embodiment then are secured firmly together by deforming the inner face of the disc, as by impacting or stamping with a die configured to form a plurality of impressions circumferentially spaced about the central axis of the yo-yo. The stamping serves to swage the disc to cause the metal of the disc to flow radially inward toward the central axis of the disc to constrict the disc tightly about the knurled surface of the locking band  60 . A circumferential groove  64  preferably is formed between the inner face  56  of the outer end of the hub  40  and the outwardly facing surface  66  of the locking band  60 . The groove  64  serves to provide space into which some of the metal (suggested at  63  in FIGS. 9 and 10) of the disc may cold flow as a result of the swaging operation. The deformed metal about the center hole  42  of the disc may flow into the groove  64  and engage the outer surface  66  of the locking band sufficiently to provide additional security to resist axial separation of the hub and the disc. 
     The swaging deforms the metal in a radially inward direction as well as causing the formation of a plurality of radially extending slightly raised ribs  88  that may be arranged in somewhat of a starburst pattern. The alternating ribs and depressions  88 ,  86  provide a less smooth annular surface that can enhance the ability of the string to become frictionally bound in the string slot near the axle of the spinning yo-yo when the yo-yo is manipulated to release tension on the string to initiate return of the yo-yo to the player. 
     The assembled yo-yo preferably includes a bearing assembly  32  to which the yo-yo string can be attached which permits the body of the yo-yo to spin with reduced frictional losses. FIG. 9 illustrates a ball bearing assembly that includes an inner race  80  and an outer race  82 . The inner race has a central hole that receives the axle  30  of the yo-yo. The inner surface of the hub  40  is configured to engage securely the inner race  80  so that the yo-yo and inner race  80  can spin relative to the outer race  82  that will be maintained stationary at the end of the string while the yo-yo is “sleeping”. To that end, inner surface of the hub  40  is provided with an annular groove  72  that defines the outer periphery of a circular land  74 . The land  74  is dimensioned to engage and clamp against the lateral side of the inner race  80  of the bearing. The radial dimension of the annular groove is large enough to receive the outer race  82  of the bearing without interfering with the ability of the outer race to spin about the axle of the yo-yo. A hole  76  is formed axially in the hub  40  and is counter-bored at its inner end at  78 . The hole  76  is threaded to securely engage the threaded end of the axle  30 . The foregoing arrangement enables the yo-yo to be assembled by placing a bearing assembly  32  on the axle and then screwing the assembled yo-yo halves onto the opposite ends of the axle. As the yo-yo halves are screwed together, they will be drawn closer together until their lands  74  engage the opposite sides of the inner race  80  of the bearing assembly, thus clamping the inner race  80  between the lands  74  of the hubs  40 . So assembled, the axle, yo-yo halves, and inner race spin as a unit relative to the outer race  82 , the yo-yo string being attached to the outer race. The dimensions of the land  74  and groove  72  are selected with respect to the bearing assembly  32  to permit the foregoing mode of operation as well as to define the width of the string slot between the two yo-yo halves. 
     The location and shape of the flared outer annular margin of the discs can be varied to vary the overall width of the yo-yo that, in turn, affects the feel of the yo-yo in the user&#39;s hand. The shape of the flared portion also may be varied in order to provide variance in the configuration of the entry to the string slot. In a preferred embodiment the disc is formed from aluminum sheet 0.125 inches thick and has a diameter of about 2¼ inches and a central hole 0.500 inches in diameter. The radially inner region of the disc may be substantially planar or may be provided with a slight deformity to provide a slight taper to the string slot. The peripherally flared portion of the disc preferably begins at about 0.825 inches radially outwardly of the central axis of the disc and preferably is provided with a relatively smooth, progressive curve that results in a total width of the stamped disc (measured axially) of about 0.45 inches. When the yo-yo is assembled, it may be configured so that it will have a string slot width of about slightly less than ⅛th inch (e.g., 0.100″) with an overall yo-yo width of approximately 1 inch. Thus, the arrangement can provide a very wide butterfly entry at the outermost periphery of the assembled yo-yo, of approximately 1 inch, that progressively narrows to the string slot. When performing string tricks, the wide entry afforded by the butterfly configuration makes it easier for the user to catch the yo-yo between the ends of a length of the yo-yo string. It should be understood, however, that although the foregoing dimensional example is a presently preferred configuration, other dimensions for the various components may be employed with departing from the scope of the invention. 
     After each yo-yo half is assembled and may have been polished in a batch process, it may be coated to apply a finishing coat as desired. A preferred finishing process may comprise applying a powder coat with the desired coloring in a conventional electrostatic process in which the piece then is baked at an elevated temperature to cause the powder to form the desired finish surface. 
     From the foregoing it should be appreciated that the invention provides a yo-yo structure and method for its construction that enables a metal yo-yo to be made with less difficulty and at substantially less expense than with prior art metal yo-yos. The construction and method of fabrication enables substantial variation in the configuration of the yo-yo. It should be understood, however, that the foregoing description of the invention is intended merely to be illustrative thereof and that other modifications, embodiments and equivalents may be apparent to those skilled in the art without departing from its spirit.