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Publication numberUS3237506 A
Publication typeGrant
Publication dateMar 1, 1966
Filing dateOct 22, 1963
Priority dateOct 22, 1963
Publication numberUS 3237506 A, US 3237506A, US-A-3237506, US3237506 A, US3237506A
InventorsHerman G Muenchinger
Original AssigneePhillips Screw Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Recessed head fasteners
US 3237506 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

March 1, 1966 H. s. MUENCHINGER 3,237,506

RECESSED HEAD FASTENERS Filed Oct. 22. 1963 4 Sheets-Sheet 1 4?: I A INVENTOR g h M ATTORNEYS March 1, 1966 MUENCHINGER 3,237,506

4 Sheets-Sheet 2 ATTORNEY 5 March 1966 H. G. MUENCHINGER 3,

Filed Oct. 22, 1963 4 Sheets-Sheet 5 INVENTOR ATTORNEYS March 1, 1965 H, MUENCHlNGER 3,237,506

RECESSED HEAD FASTENERS Filed Oct. 22, 1963 4 Sheets-Sheet 4 INVENTOR fzer'mrz Gflwezzrizge' r ATTORNEYS United States Patent 3,237,506 RECESSED HEAD FASTENERS Herman G. Muenchinger, Chaplin, Conn., assignor to Philiips Screw Company, East Boston, Mass, 21 corporation of Delaware Filed Oct. 22, 1963, Ser. No. 318,054 13 Claims. (Cl. 85-45) This invention relates to threaded fasteners, and more particularly to recessed head fasteners of the cross-recessed type exemplified in an early form by US. Patent No. 2,046,839 to Phillips. The present application is a continuation-in-part of Serial No. 811,105, filed May 5, 1959 (now abandoned), and combines therewith a portion of the disclosure of Serial No. 112,836, filed May 26, 1961 (now abandoned).

Threaded fasteners having tool-engaging recesses of the Phillips type have been Widely and successfully used throughout the world, the recess now in most widespread use being that disclosed in US. Patent No. 2,474,994, to Tomalis. The latter recess represents an improvement over the original Phillips recess, in that the side walls of the grooves of the Tomalis recess are much more nearly parallel to each other, thus reducing the throwout tendency, as pointed out in the Tomalis patent. Decreasing the throw-out tendency, of course, permits a greater torque to be applied through a driving tool before the latter tends to be thrust axially out of the recess by virtue of the vertical or throw-out component of the applied torque.

The recess disclosed and claimed in said patent, and now in world-wide use, has an included horizontal angle of from 2 to 4 and an inclined vertical angle of 8 to 10 between the opposed side walls of each groove, said said walls converging outwardly and also downwardly. The horizontal angle is that angle defined by the intersection of the side walls of the groove with a plane at right angles to the axis of the screw. The vertical angle is the angle defined by the intersection of the side walls of the groove with a plane extending parallel to the axis of the screw and at right angles to the radial plane of symmetry of the groove. As pointed out in the said patent, the throw-out component of the applied torque was reduced, by the construction there patented, to the lowest factor consistent with good engineering principles, the patentee pointing out that it would be desirable to reduce the aforesaid vertical angle to zero degrees, but that this was not deemed practicably possible, that is, by means and methods then known to him.

In copending applications Serial No. 811,105, filed May 5, 1959, and Serial No. 112,836, filed May 26, 1961 (both now abandoned), the applicant has disclosed further improvement of the Phillips recess, which improvements form the subject matter of the present application.

As explained in said copending applications, a widespead use of recessed head fasteners lies in so-called self-tapping applications in which the fasteners are driven into previously drilled but untapped holes in metals, plastics, etc. The successful use of self-tapping fasteners requires that the driving recesses have high torque capacity, easy entry by the driving tool, and provision for maximum stability of the driving tool in the recess. High torque capacity, of course, involves reduction or elimination of the aforementioned throw-out tendency, among other things, while maximum stability of the driver in the recess requires accurate mating of the driver bit and the fastener recess, plus a wedging of the former in the latter. The ease of entry of the driving tool into the recess depends upon the area and vertical taper of the recess, which also affect the ultimate strength of the driving tool and thus the ultimate torque capacity of the driver and fastener combination.

In order to be commercially successful, recessed head fasteners must be capable of manufacture by the twoblow header technique, which involves striking the end of the wire or other material of which the fastener is made, while the same is supported in the die of the heading machine, first with a tool which forms a bloom on the end of the fastener blank and then with a further tool which finishes the head and forms the driver-engaging recess therein. This operation is carried out automati cally and at high speed.

Experience has shown that the accurate conformance of the material of the fastener blank with the recess-forming punch is very difiicult to achieve, because of the phenomenon known as metal fail-away which occurs during punching of the recess. The lack of such accurate conformance, however, enhances the aforementioned throw-out tendency, and also reduces driver stability or, in other words, tends to promote wobbling of the driving tool in the recess which adversely affects assembly line manufacturing and, of course, reduces the torque capacity of the fastener and tool couple. In the aforesaid copending application Serial No. 811,105, I have described and claimed a recess which is so designed as to reduce, to a considerable extent, the adverse effects of metal fall-away in the cold heading of recessed head fasteners. Copending application Serial No. 112,836 discloses an improved recess design, which still further reduces the fall-away effect encountered in the punching of such recesses. The present application combines the two aforesaid disclosures.

As explained in co-pending application Serial No. 811,105, metal fall-away in the punching of recessed fastener heads involves two phenomena which may be described as plowing and pull-away. The first results from the outward impetus given to the material of the fastener head by the impact of the penetrating punch. Pull-away, on the other hand, depends upon the ratio between the maximum and minimum radii of the recess and the greater this ratio, the greater the pull-away. That is to say, in producing a recess in which the radial extent of the grooves is several times the radius of the central recess portion, the metal of the sectors between the grooves will be pulled outward to a considerably greater extent than in the case of a recess in which the radial extent of the grooves is only moderately greater than the radius of the central recess portion. This is due to an effect which may be roughly likened to the effect of the surface tension in a liquid. The recess described and claimed in application Serial No. 811,105 is so designed as to reduce the pull-away effect, and the recess of Serial No. 112,836 is so designed as to make a still further reduction in such pull-away effeet. Moreover, the design of the latter recess is such as to permit the use of a punching tool and method which are designed to minimize the over-all fall-away effect, whether due to plowing or to pull-away, by causing a metal flow toward those surfaces of the recess from which the metal would otherwise fall away. This flow of metal toward the last-mentioned recess surfaces occurs during the final stage of the punching of the recess, whereby the metal fall-away which may have already commenced is retarded or compensated, the result being a finished recess in which the conformance of the metal I of the fastener head to the header punch is considerably torque be applied without driver throw-out, but the same driver bit can be employed for driving a much greater number of fasteners before it must be discarded due to wear of the driver surfaces.

It has long been known that the throw-out tendency could be largely or completely eliminated, and the torque capacity of recessed head fasteners thus increased, if the groove side walls could be made vertical, i.e., without vertical taper, and several screw recess designs including such vertical groove side walls have been proposed, but no such design has heretofore received commercial acceptance because of the impossibility of producing such fasteners by the cold heading technique. I have discovered a method whereby, with the use of a special punch made in accordance with the disclosures of the aforesaid copending applications, it is possible to produce by the rapid, automatic cold heading technique, fasteners having a tool-engaging recess of which the groove side walls, over a major portion of their area, are substantially or precisely vertical, such recess constituting one aspect of the present invention. Fasteners provided with the novel recess can be driven by the use of driving tools now in use for driving fasteners provided with the Tomalis recess, but the best results are obtainable by use of a novel driving tool also described in said copending applications.

While the present invention is particularly applicable to self-tapping screws, in which the torque demands are likely to be highest, and to screws of the protruding head type in producing which the metal fall-away problem is greatest, it is also applicable to other types of recessed head fasteners, inluding fasteners for practically all uses and having various head types including flat head or countersunk screws and bolts.

Accordingly, it is an object of the present invention to provide a threaded fastener having a tool-engaging recess extending into its upper end along its longitudinal axis and comprising a central portion and grooves radiating therefrom, the walls of said central portion between each pair of adjacent grooves being formed to provide one or more valleys extending from the upper end of the fastener toward the bottom of the recess, said valley or valleys being laterally bounded by generally axially ex tending tool-engaging surfaces. Some or all of the added tool-engaging surfaces may incline inwardly, that is to say, taper downwardly toward the fastener axis. Preferably, the above-mentioned valleys are substantially triangular in horizontal section and of downwardly diminishing sectional area.

A further object of the invention is the provision of a recessed head fastener of the type defined in the preceding paragraph, in which the tool-engaging surfaces of each aforesaid valley mutually intersect in a line which is inclined downwardly toward the fastener axis at an angle greater than about and optimally about 14. Such tool-engaging surfaces need not, however, intersect to form a sharp dihedral angle. If a plurality of valleys are provided between the grooves of each adjacent pair, they may be closely adjacent or may be separated by an intervening rib of curved or angular transverse section.

Preferably, the aforesaid valleys will extend from the top of the fastener head to the bottom of the recess, i.e., to the plane of junction between the grooves and the central recess portion. However, if desired, the valleys may diminish to zero at a point above said plane.

The provision of valleys between the grooves of a screw recess of the type in question enables the production and use of recesses having nearly vertical groove side walls, as shown in the drawings, thus improving their torque capacities, because (1) the necessary wedge fit between the screw and driver takes place along the bottoms of the valleys, which are at a substantial angle to the screw axis and (2) reduction of metal fall-away, by hypothesis, promotes conformity between the metal of the fastener and the surfaces of the punching tool, thus facilitating the production of such nearly vertical walls by means of a tool of appropriate design.

It is a further object of the present invention to provide a threaded fastener made of..metal and having a toolengaging recess extending to its upper end along its longitudinal axis, which recess comprises a central portion and a plurality of more than two equiangularly spaced grooves radiating from the central portion, the side Walls of said grooves being substantially vertical over a major portion of their respective areas, the metal of the upper end of the fastener being formed to provide a depression between the grooves of each mutually adjacent pair of grooves and said metal being work-hardened in the regions between each said side wall and the adjacent depression.

A further object is the provision of fasteners as defined in the preceding paragraph, in which each said depression extends to and communicates with the aforesaid central recess portion. The depressions may take any suitable form but are preferably V-shaped in transverse section, and preferably decrease in cross-sectional area as they extend outwardly from the said central recess portion.

The depressions formed in the upper end of the fastener may constitute, in effect, generally horizontal extensions of the generally vertical valleys provided, as aforesaid, in the walls of the central recess portion.

Accordingly, it is an object of the present invention to provide a threaded fastener as defined above, the wall of the central portion between the grooves of each mutually adjacent pair of grooves being formed to provide a valley extending from the upper end toward the bottom of the recess, said valley being laterally bounded by generally axially extending tool-engaging surfaces, said valley being of downwardly diminishing sectional area, the metal of the upper end of the fastener being formed to provide a plurality of depressions each communicating with the upper end of one of said valleys and extending radially outwardly therefrom. These depressions may take any suitable form, but are preferably formed as mentioned above.

Other and further objects, features and advantages will be apparent from the description which follows, read in connection with the accompanying drawings, in which:

FIGURES 1 and 2 are illustrative of the prior art, showing in plan and axial section, respectively, a recessed head fastener with the tip of a driving tool inserted in the recess thereof;

FIGURE 3 is a plan view of a fastener head provided with a recess according to the invention, and with the tip of a driving tool inserted therein;

FIGURES 4, 5 and 6 are fragmentary sectional views taken on line 44, 55 and 66 of FIGURE 3;

FIGURE 7 is a plan view of a modified recess according to the invention;

FIGURES 8 and 9 are fragmentary axial sections on lines 88 and 9-9, respectively, of FIGURE 7;

FIGURE 10 is a plan view of a further modification of the recess of the invention;

FIGURE 11 is a fragmentary axial section on line 11-11 of FIGURE 10;

FIGURE 12 is a plan view of the head of a fastener provided with a recess according to another embodiment of the present invention;

FIGURE 13 is a side view, partly in section on line 1313 of FIGURE 12;

FIGURE 14 is a vertical section on line 14-14 of FIGURE 12;

FIGURE 15 is a fragmentary vertical section on line 15-15 of FIGURE 12;

FIGURE 16 is a view similar to FIGURE 14 illustrating the application of the present invention to a flat head screw;

FIGURE 17 is a fragmentary vertical sectional view illustrating a modification of the embodiment illustrated in FIGURE 14;

of the prior art screw recess of FIGURE 1.

FIGURE 18 is a plan view of a fastener head provided with an alternative recess according to the invention; and

FIGURE 19 is a fragmentary vertical section on line 19-19 of FIGURE 18.

In order to facilitate an understanding of the invention, reference is made to the embodiments thereof shown in the accompanying drawings and detailed descriptive language is employed. It will nevertheless be understood that no limitation of the invention is thereby intended and that various changes and alterations are contemplated such as would ordinarily occur to one skilled in the art to which the invention relates.

The recess of the present invention is applicable to most types of threaded fasteners, including bolts, screws and the like, the fasteners depicted being designated, for convenience, as screws. The screw of FIGURES 1 to 15, inclusive, is of the protruding head type, the underside 40 of the head portion 41 (FIG. 13) being flat and disposed at 90 to the axis of the cylindrical shank portion 42. Protruding head screws may have various head contours, some of which are known as pan head, truss head, oval head, etc. The unthreaded blanks for such screws are conventionally formed in a two-blow cold header, the material, in wire form, being supported in a die provided with a flat exposed end surface corresponding to the fiat under surface 40 of the head 41. The wire end protruding from the header die is struck with a first punch which forms a bloom or enlargement of the protruding wire portion, and then with a second punch having a concavity formed in the working end thereof, the punch nib projecting from the center of such concavity. The second punch imparts the rounded upper surface to the head portion 41 of the screw and, at the same time, forms therein a tool-engaging recess.

Referring to FIGURES 1 and 2, the fastener head is provided with a recess 11 produced by cold heading in the usual manner, the recess being typical of those resulting in the commercial production of recessed head fasteners of the type disclosed in US. Patent No. 2,474,994. As will be seen in FIGURE 2, the metal of the head has fallen away, in the punching operation, as indicated at 12 to such an extent that the chord 13 of the corresponding curve makes an angle of 10 to 15 with the fastener axis 14. For clarity of illustration, this angle has been somewhat exaggerated in FIGURE 2. The metal fall-away phenomenon occurs in the recess forming operation, qualitatively though not necessarily quantitatively in the manner illustrated. In the usual case, the noticeable fallaway begins at a point approximately one-half to twothirds of the recess depth, measured from the bottom of the recess. The result is a poor fit of the driving tool 15 in the recess, allowing the latter to wobble very noticeably, particularly when the necessary end thrust is applied in order to keep the driver seated in the recess during starting of the screw in the workpiece. In addition the wobble diminishes the torque capacity of the driverfastener combination illustrated. As is clear from consideration of FIGURES 1 and 2, this torque capacity is further greatly affected by the diminution of the area of driving contact between the driving tool and the fastener recess.

FIGURES 3 to 6 illustrate a fastener head provided with a recess 16 made according to the present invention, FIGURE 3 also showing the tip of a driving tool 17 in transverse section. The recess extends into the upper end of the fastener head lit-a along the longitudinal axis 14 of the fastener and comprises a central recess portion 18,

'best seen in FIGURE 4, and four angularly spaced generally radial grooves 19 extending outwardly from the central portion 18. A radial groove 19 having opposite side walls 19' is seen in vertical section in FIGURE 6. The opposite side walls 19' of the groove 19 are, as shown in FIGURE 6, more nearly vertical and, as shown in FIG- URES 3, 7 and 10, are more nearly parallel than those This disposition greatly increases the torque capacity of the recess and correspondingly reduces the cam-out tendency due to the axial component of the applied torque.

Between each mutually adjacent pair of grooves 19 the wall of the central portion 18 is formed to provide a valley 20 bounded by mutually inclined lateral surfaces 21 and 22 which intersect in a line 23. Each valley 20 extends downwardly from the upper surface of the head 10a to the plane at which the grooves 19 intersect the recess central portion 18. The central portion 18 preferably terminates downwardly in a generally conical depression 24.

Each of the lateral surfaces 21 and 22 of each valley 20 is inclined downwardly toward the axis of the fastener at such an angle that their line 23 of intersection lies at an inclination of between about 10 and 15 to the fastener axis. This line of intersection, which represents the bottom of the valley in question, may thus be made to incline at approximately the same angle as the natural angle of fall-away of the material of which the fastener is being fabricated and in this manner fall-away in the vicinity of the valley bottoms is completely or substantially compensated. Accordingly, a correspondingly shaped driving tool will mate substantially exactly with such a recess, at least in the Vicinity of the several valley bottoms, all the way from the top to the bottom of the recess, thus promoting great stability of the tool in the recess, and permitting a wedging action between the tool and the recess, despite the nearly vertical groove side walls. Moreover, due to the decrease in the ratio of the greatest radius of the recess to the smallest radius thereof (in any plane normal to the fastener axis) the pull-away effect of the punching operation is considerably reduced with the result that the only noticeable fall-away of metal occurs along the upper portions of the ridges or ribs 25 separating the valleys 20 from the grooves 19, which ribs are inclined to the screw axis at a lesser angle than that of the line 23, and are convexly arcuate in horizontal section. The fall-away in these areas is of relatively slight extent, leaving substantial areas of the lateral surfaces 21 and 22 to mate exactly with the corresponding surfaces of a driving tool, thus considerably increasing the driving contact area between tool and fastener. The over-all result of this improvement in the design of fastener recess and corresponding driving tool is to improve greatly the stability of the driver-fastener combination, as well as to increase substantially the torque capacity of the couple, in both driving and fastener-removal directions. A comparison between FIGURES 1, 2 and 3, 4 readily illustrates such over-all result. Thus, the driving contact between the walls of each valley 23 (FIG. 3) and the corresponding driver extends throughout the full depth of the recess, as contrasted with the situation depicted in FIGURES 1 and 2, in which there is no contact between the driver and the central recess walls over the upper onethird of the recess.

Referring now to FIGURES 7, 8 and 9 the fastener head 19b is provided with a recess 30 which diifers from the recess 16 of FIGURES 3-6 in that two valleys 31 are provided between the grooves 19 of each adjacent pair. Each valley 31 is bounded by lateral surfaces 32 and 33, the surfaces 33 lying in planes substantially parallel to the fastener axis 14 while the surfaces 32 lie in planes which slope inwardly and downwardly toward the axis 14. The valleys 31, in the illustrated embodiment, are separated by a rib 34 bounded by two intersecting plane surfaces 35 and 36, the rib 34 corresponding generally to the ribs between the grooves of the recess disclosed in United States Patent No. 2,474,994, mentioned above. If desired, however, the ribs 34 may be diminished in width by increasing the size of the valleys 31, or may be eliminated completely by introducing further valleys between the valleys 31. In either case, the benefits of the invention, as described in connection with the embodiment of FIGURES 3-6, will be at least partly realized,

since the effect of metal fall-away will be substantially fully compensated in the vicinity of the bottoms of the valleys, and the total driving contact area of the recess will be increased.

FIGURES 10 and 11 illustrate a further modification in which the fastener head 10c is provided with a recess 37 which differs from that illustrated in FIGURES 3-6 in that the valley 20 between each pair of adjacent grooves 19 diminishes in depth and cross-sectional area to a zero value at a point above the plane at which the grooves 19 merge with the central recess portion 18. The bottom of the valleys 20 incline to the fastener axis 14 at an angle of between 10 and 15, as before, while the angle of inclination of the lower wall portions of the central recess is at the conventional value of about "-7". The modifications illustrated in FIGURES 7 and 10, respectively, may of course be combined in a single recess if desired. 1

The recess 43 of FIGURE 12 comprises a central portion 44 and a plurality of radial grooves 45 extending outwardly from the central portion 44. Four grooves 45 are shown in each of the several embodiments illustrated herein, but it will be understood that any reasonable number, greater than two, of grooves 45 may be employed. The grooves 45 are equiangularly spaced. Each groove 45 is formed with a clockwise side wall 46, an anti-clockwise side wall 47 and a bottom wall 48, the latter being inclined inwardly and downwardly to join the generally conical bottom 49 of the central recess portion 44. The grooves 45 are separated by intervening promontories of metal designated, for convenience, as ribs 50 and, in the illustrated embodiment, each rib 50 is provided with a valley 51 extending from the upper end of the central recess portion 44 to the bottom 49 thereof. Each valley 51 is bounded by walls 52 and 53 which form tool-engaging surfaces of the recess 43, supplementing the groove side walls 46 and 47 in the transmission of driving or removal torque. Each of the valley walls 52 and 53 is inclined downwardly toward the screw axis at such an angle that their line of intersection 54 lies at an inclination of between about and to the screw axis. This line of intersection, which represents the bottom of the valley in question, may thus be made to incline at approximately the same angle as the natural angle of fallaway of the material of which the fastener is fabricated and, in this manner, fall-away in the vicinity of the valley bottom is completely or substantially compensated. Accordingly, as explained in connection with FIGURES 3-6, a correspondingly shaped driving tool will mate accurately with such a recess, at least in the vicinity of the valley bottoms, all the way from the top to the bottom of the recess, thus promoting stability of the driving tool in the recess and permitting a wedging action between the tool and the recess. Such wedging action and the corresponding stability are important in insuring proper application of the screws to the work.

As mentioned above, the provision of substantially vertical groove side walls is recognized to be advantageous from the standpoint of reducing or eliminating throw-out. However, it has heretofore been impractical to produce a screw recess having vertical groove side walls because of the metal fall-away phenomenon. A further reason why recesses having such vertical groove side walls have not been used, resides in the fact that the nearer vertical the groove side walls and corresponding wing walls of the driver are made, the less wedging action can take place between the driver and screw. As a practical matter, due to the clearance necessary to permit driver entry into the recess, and to manufacturing tolerances, such wedging has been actually impossible as the groove walls approach vertical. As a result, the driver bottoms in the screw recess and is subject to the objectionable wobbling or misalignment hereinbefore mentioned. As pointed out above, the provision of the valleys 51 of FIGURE 12 enables wedging of the driver in the recess even though the groove side walls are nearly or completely vertical and, moreover, the formation of such valleys during the punching operation overcomes to a considerable extent the problem of metal fall-away, thus enabling the groove side walls to be made more nearly vertical than has heretofore been practical. By reason of the present invention, and particularly the feature now to be described, the groove side walls may be made substantially vertical, or precisely vertical, or one of the walls of each groove may even be given a slight negative inclination (undercut) by a conventional two-blow cold heading This result is achieved by means which elim technique. inate or compensate, to a greater degree than heretofore possible, the effect of metal fall-away in the punching of screw recesses.

Referring again to FIGURES 12-14, it will be seen that each rib 50 between grooves is provided with a notch or depression 55 which extends from the central recess portion 44 radially outwardly to a distance approximating the radial extent of the grooves 45. The depressions 55 may take any suitable shape but preferably, as illustrated in FIGURES 12-14, they take the form of generally horizontal extensions of the inclined or generally vertical valleys 51 of the recess. The depressions 55 are preferably V-shaped in transverse section and may comprise a straight bottom element joining the bottoms of the valleys 51 with a short radius as seen at 56 in FIGURE 14. Alternatively, the depressions may have a curved bottom profile as indicated by the curved bottom 57 of the depression 55 seen in FIGURE 17.

The depressions 55 are formed by correspondingly shaped portions of the heading punch disclosed in copending application Serial No. 314,828, filed September 4, 1963, such punch portions penetrating the metal of the screw head only during the final increments of movement of the punch toward and into the screw blank. As a result of such penetration of the upper surface of the screw head, the metal of the latter is caused to flow in directions normal to the side walls 58 of the depressions, thus in directions toward the side walls 46 and 47 of the grooves 45. Stated differently, the flow of metal away from the punch ribs forming the grooves 45, due to the fall-away phenomenon mentioned above, is retarded or compensated by the formation of the depressions 55 to such an extent that the groove side walls 46 and 47 will conform closely to the ribs of the recessforming punch, and may be made vertical for all practical purposes.

The punching of the depressions 55 into the upper surface of the screw head, during the final movement of the header punch, also reduces fall-away of the metal forming the ribs of the recess. This effect is illustrated in FIGURE 15 wherein the broken line 59 illustrates, diagrammatically, a typical curvature of the upper portion of a valley wall 52, 53 caused by metal fallaway prior to the discovery of the present feature of the invention. An important correction of this condition is designated by the solid outline of the wall surface 52, from which it will be noted that the fall-away effect is confined to a narrow area adjacent the upper end of the wall 52, thus promoting proper engagement between the driver and the screw recess over a considerably greater area of the latter than has heretofore been possible. As mentioned above, this increases the torque capacity of the couple, as well as improving stability of the driver in the recess, and increasing the useful life of the driver.

FIGURE 16 illustrates the application of the present invention to a flat head or countersunk, screw in which the upper surface 60 of the screw head is flat, while the under surface 61 is conical. In this case, in order to terminate the depressions at a suitable radial distrance from the screw axis, the bottoms 62 thereof are inclined upwardly at a substantialangle. The corresponding punch is illustrated in copending application Serial No. 314,828.

In FIGURE 17 the bottom of depression 55' is vertically curved throughout.

FIGURES 18 and 19 illustrate an embodiment of the invention as applied to an otherwise conventional screw recess as now in widespread use, namely, the recess of the aforesaid Tomalis patent. The recess comprises generally a central portion 63 and radial grooves 64 separated by ribs 65. Centrally of each rib 65 there is provided a radial depression 66 similar to the depressions 55 of FIGURE 12 except that the recess in question is not provided with the valleys 51 of FIGURE 12. The depressions 66 of FIGURE 18 therefore terminate inwardly in a V-shaped notch disposed centrally of the upper end of each rib 65. The effect of forming the depressions 66 in the screw head of FIGURE 18 is partially to eliminate or compensate for the fall-away otherwise encountered in punching screw recesses of this type, and thus to promote driver stability and increase torque capacity as mentioned above. Another effect achieved, both in the embodiment of FIGURE 12 and that of FIGURE 18, is that the metal between each depression 55 or 66, as the case may be, and the adjacent groove side walls is strengthened by work-hardening, thus lessening the tendency for the groove side walls to be deformed by the driving tool in the application of high torques, and thereby increasing the overall torque capacity of the recess. Another advantage applicable to both recesses lies in the fact that the walls of the depressions 55 and 66 form auxiliary tool-engaging surfaces when used with a complementary driving tool, thus adding a further increment to the over-all torque capacity of the screw and driver couple.

By any suitable machining or metal working technique which is adapted to quantity production, driving tools are made to have substantially the same tip form as that of the punch nibs used in the formation of the described recesses, so as to make the best possible engagement with the screw recesses produced by use of the above-mentioned header punches. By virtue of necessary manufacturing tolerances, however, the driver tips will vary somewhat from the precise dimensions of the punch nibs to provide the small clearances needed for ready entry of the driving tools into the screw recesses. Notwithstanding the aforesaid clearances, however, and for the reasons elaborated at the outset of the specification, the driving tools will make excellent and stable engagement in the recesses, and the screw and driver couples, according to the present invention, will have substantially greater torque capacity and improved stability as compared with those now in use.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A threaded fastener made of metal and having a tool-engaging recess extending into its upper end along its longitudinal axis and comprising a central portion and a plurality of angularly spaced grooves radiating therefrom, the side walls of said grooves being substantially vertical over a major portion of their respective areas, the upper surface of the metal of said upper end being formed to provide a depression extending outwardly from said central recess portion between the grooves of each mutually adjacent pair of grooves, said depressions extending outwardly to a distance from said axis which is substantially greater than the distance from said axis to the points of intersection of said grooves with said central portion at the upper surface of said upper end, whereby substantial portions of said depressions are radially co extensive with substantial portions of the upper edges of said groove side walls, and said metal being work-hardened in the regions between each said side wall and the adjacent depression.

2. A threaded fastener as defined in claim 1, said depressins being V-shaped in transverse section.

3. A threaded fastener as defined in claim 2, said depressions progressively decreasing in transverse sectional area as they extend outwardly from the said central recess portion.

4. A threaded fastener having a tool-engaging recess extending into its upper end along its longitudinal axis and comprising a central portion and a plurality of angularly spaced grooves radiating therefrom, the side Walls of said grooves being substantially vertical over a major portion of their respective areas, the wall of said central portion between the grooves of each mutually adjacent pair of grooves being formed to provide a valley extend ing from the said upper end toward the bottom of said recess, said valley being bounded by generally axiallyextending tool-engaging surfaces, said valley being of downwardly diminishing sectional area, the upper surface of the metal of said upper end being formed to provide a plurality of depressions each communicating with the upper end of one of said valleys and extending radially outwardly therefrom to a distance from said axis which is substantially greater than the distance from said axis to the points of intersection of said grooves with said central portion at the upper surface of said upper end whereby substantial portions of said depressions are radially coextensive with substantial portions of the upper edges of said groove side walls.

5. A threaded fastener as claimed in claim 4, said depressions being V-shaped in transverse section.

6. A threaded fastener as claimed in claim 5, said depressions progressively decreasing in transverse sectional area as they extend outwardly from the said central recess portion.

7. A threaded fastener made of metal and having a tool-engaging recess extending into its upper end along its longitudinal axis and comprising a central portion and a plurality of angularly spaced grooves radiating therefrom, the side walls of said grooves being substantially straight over a major portion of their respective heights in the direction longitudinally of said fastener, the metal of said upper end being laterally displaced by an indentation formed between the grooves of each mutually adjacent pair of grooves, said indentation being elongated and extending in the radial direction between said grooves to a distance substantially no further from said axis than the outer ends of said grooves, whereby the metal adjacent the upper surface of said fastener is compacted in a direction normal to said longitudinal axis and in a direction substantially normal said side walls.

8. A threaded fastener having a tool-engaging recess extending into its upper end along its longitudinal axis and comprising a central portion and four equiangularly spaced grooves radiating therefrom, said grooves having side and bottom walls, the wall of said central portion between each mutually adjacent pair of grooves being formed to provide a valley extending from the said upper end toward the bottom of said recess, said valley being laterally bounded by mutually inclined generally axially extending tool-engaging substantially planar surfaces, said surfaces of each valley intersecting with one another along a line which is inclined downwardly toward said axis at an angle of between about 10 and about 15, so that each valley is of substantially V-form in horizontal section, and of downwardly diminishing sectional area, the plane containing the line of intersection of said surfaces and bisecting each said valley being substantially radial, the wall of said central portion intermediate each valley surface and the adjacent groove side wall, and merging with each, being of convex configuration in horizontal section, and, over the major portion of its vertical extent beginning from the bottom, being downwardly inclined toward said axis at an angle of inclination less than that of said valley intersection line.

9. A threaded fastener as defined in claim 8, the metal of said upper end being formed to provide a depression between the grooves of each mutually adjacent pair of grooves and said metal being work-hardened in the regions between each said side wall and the adjacent depression.

10. A threaded fastener as defined in claim 8, the metal of said upper end being formed to provide a plurality of depressions each communicating with the upper end of one of said valleys and extending radially outwardly therefrom.

11. A threaded fastener as claimed in claim 10, said depressions being V-shaped in transverse section.

12. A threaded fastener as claimed in claim 11, said depressions progressively decreasing in transverse sectional area as they extend outwardly from the said central recess portion.

13. A threaded fastener having a tool-engaging recess extending into its upper end along its longitudinal axis and comprising a central portion and four equiangularly spaced grooves radiating therefrom, said grooves having side and bottom walls, the wall of said central portion between each mutually adjacent pair of grooves being formed to provide a valley extending from the said upper end toward the bottom of said recess, said valley being laterally bounded by mutually inclined generally axially extending tool-engaging substantially planar surfaces, said surfaces of each valley intersecting with one another along a line which is inclined downwardly toward said axis, at an angle corresponding substantially to the natural angle of metal fall-away, so that each valley is of substantially V-form in horizontal section, and of downwardly diminishing sectional area, the plane containing the line of intersection of said surfaces and bisecting each said valley being substantially radial, the wall of said central portion intermediate each valley surface and the adjacent groove side wall, and merging with each, being of convex configuration in horizontal section and, over the major portion of its vertical extent beginning from the bottom, being downwardly inclined toward said axis at an angle of inclination less than that of said valley intersection line.

References Cited by the Examiner UNITED STATES PATENTS 2,140,449 12/1938 Brown 8545 2,173,707 9/1939 Brown 8545 2,377,114 5/ 1945 Tomalis. 2,395,476 2/1946 Givnan 8545 2,588,404 3/ 1952 Muenchinger 8545 2,914,984 12/1959 Ansengh 8545 FOREIGN PATENTS 662,318 12/ 1951 Great Britain.

EDWARD C. ALLEN, Primary Examiner.

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Classifications
U.S. Classification411/404, 411/919
International ClassificationF16B23/00
Cooperative ClassificationF16B23/0023, Y10S411/919
European ClassificationF16B23/00B4