CLINCH SPOT BEARING

RELATED APPLICATION This patent application is related to provisional patent application serial

number 60/745,897 entitled "Clinch Spot Bearing" filed on April 28, 2006, priority from which is hereby claimed. FIELD OF THE INVENTION The present invention relates to a fastener for joining two sheets of material which also permits relative rotation between them. More specifically, it relates to a clinch-type two-part fastener which provides the rotatable joinder of

two sheets in a single pressing assembly operation. BACKGROUND OF THE INVENTION There is recognized in the fastening arts the need for a fastener which will rotatably join two relatively thin sheets of metal. These fasteners are often referred to as pivot bearings or thrust bearings. Examples of such structures are shown for example in U.S. Patent 4,582,435 issued to Davis entitled "Pivot Bearing." Another such device is described in U.S. Patent 5,860,780 issued to Lenac et al. In both cases, a riveting type process is used to flare over either one of the material sheets or a rivet type fastener as depicted in the patent to Lenac et al. Each of these systems has their disadvantages which include the inability to provide a resilient separation between the sheets or to accommodate axial deflection without impairing the relative rotation between the sheets.

Furthermore, installation of the Lenac fastener into the sheets can be complicated. Also, in both of these instances, one of the bearing surfaces is necessarily the

sheet material itself. This can result in excessive wear, maintenance problems, and failure of the joint. It also limits the sheet material and its surface condition. Joint assemblies which solve this problem are more complicated, three-component systems. There is therefore a need in the art to join two sheets of relatively thin sheet metal while allowing rotation between them in a manner which is efficient and economical and which also allows for axial deflection and resilient separation between the sheets. There is also a need in the art for a simplified rotatable joint assembly for thin metal sheets in which neither of the sheets is required to be a frictional bearing surface. SUMMARY OF THE INVENTION In order to meet the needs in the art described above, the present invention

permits rotatable joinder of two sheets by providing a two-piece interfitting bearing assembly with the individual elements rigidly attached to each sheet so that the sheets are joined but rotation is controlled by the interfitting bearing surfaces. The two interfitting parts comprise an inner and outer race which may be placed together in superposition with aligned apertures in the sheets to be joined before the race pair is pressed into the sheets in a single pressing operation. Material for the bearing components may be selected for the friction and load characteristics of the specific application. Alternate embodiments include adding ball bearings between the races or in another case utilizing a biasing spring between the sheets with arcuate bearing surfaces which permits the sheets to rotate and/or deflect angularly. More specifically, the present invention comprises a bearing assembly for

rotatably joining two sheets, a top sheet having a first aperture aligned with a bottom sheet in face-to-face relation with the bottom sheet having a second

aperture in alignment with the first aperture about an axis. An outer race resides within the aperture of the top sheet and has a bore in the center and means around its circumference for receiving a cold flow of metal from the top sheet to rigidly attach it. An inner race lies partially within the outer race and partially within the second sheet, secured thereto by circumferential clinch attachment means. The inner race further includes a head of increased diameter greater than the diameter of the outer race bore thereby captivating the top sheet to the bottom sheet after assembly. The inner race and the outer race are closely dimensioned to provide the joinder and rotatability of one sheet relative to the other about the axis. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a bottom right isometric assembly view of the invention. Figures 2A and 2B are sequential side sectional views showing the assembly of the invention. Figure 3 is a side sectional view of an alternate embodiment thereof using a spring separator and arcuate bearing surfaces. Figure 4 is a side sectional view of an alternate embodiment showing the use of ball bearings. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figure 1, the basic four elements of the present invention are shown. Inner race 11 and outer race 13 are assembled into sheets 15 and 17

such that they become joined yet freely rotatable upon bearing elements 11 and 13. Element 11 is an inner race which is interfϊtted within outer race 13. In a

single pressing operation as depicted in Figures 2 A and 2B, inner race 11 is

installed into the bottom sheet 17 as outer race 13 is clinched into top sheet 15.

Installation of the races is achieved through aligned apertures 16 and 18 in the top

and bottom sheets respectively. Referring now to Figures 2 A and 2B, assemblage of the components of the invention is illustrated by a pressing operation carried out between punch 21 and

anvil 23. Top and bottom sheets 15 and 17 are placed in the press with their

apertures aligned. Inner race 11 and outer race 13 are placed together and set onto the sheets in axial alignment with the sheet apertures as shown in Figure 2A. Pressing is then performed which results in the joinder of the sheets and the clinching of parts as depicted in Figure 2B. A circumferential undercut 31 around

the perimeter of the outer race receives the cold flow of metal from the top sheet while a similar circumferential undercut 33 on the inner race receives the cold

flow of metal from the bottom sheet due to the pressure of these parts into the sheet material. This achieves the rigid affixation of the outer race to the top sheet and the inner race to the bottom sheet. The parts are sized to create a gap or clearance 35 to control the relative movement between the parts and to permit their free rotation. Referring now to Figure 3, an embodiment of the invention utilizes an inner race 11 having an elongated shank portion 41 which permits a substantial

standoff distance between sheets 15 and 17. The inner race 11 and outer race 13

are clinched into the top and bottom sheets in the same manner as shown in the embodiment of Figures 2 A and 2B but a spring 43 is employed around the shank

41 of the inner race. The spring resiliently biases the sheets apart while permitting their angular deflection as shown in this figure. This embodiment

permits a rocking motion as well as a rotary motion between the parts. To facilitate the angular deflection, compatible arcuate surfaces 44 and 45 on the inner and outer races respectively are employed. This embodiment provides a ball-and-socket style flush clinch bearing but requires a two-step pressing operation for installation. The outer race is pressed into the sheet first and then

the inner race is installed through the top sheet and spring, being clinched into the second sheet with a second pressing operation. Referring now to Figure 4, yet another embodiment rotatab Iy joins sheets

15 and 17 in which the inner and outer races 11 and 13 employ ball bearings 46 to reduce friction. A further reduction of friction may be obtained by utilizing a

shim (not shown) between the sheets during installation which when later removed ensures that the sheets will be maintained in a non-contacting relationship as they rotate. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.