SCREW TYPE FASTENER,AND ITS MANUFACTURE

Abstract: A threaded fastener having a head (11) with a convex slot (13) and a shank (2). A driving tool having a blade with a leading edge of complementary shape to the convex base of the fastener slot. A method and apparatus for forming the threaded fastener by (a) cold forming a fastener blank (1); (b) punching the blank with a punch (5) in a die (4) and (c) forming the thread on the shank (2) in a roll former (15).

Description: SCREWTYPEFASTENER,ANDITSMANUFACTURE This invention relates to an improved threaded fastener, and an apparatus and method for producing same and a driving tool such as a screw-driver for use with the fastener. For convenience, the present invention is described in relation to a screw but it is equally applicable to other fasteners. BACKGROUND ART Hitherto conventional screws (i.e., wherein the base wall of the screw slot is s-ubstantially planar or flattened) , although useful in situations wherein minimal effort is only required by the user (e.g., when the screw has to be driven into relatively soft material such as softwood) have proved deficient for use when required to be driven into relatively hard material, for example hardwood such as red gum and Oregon. This problem has been even more pronounced when the housewife herself wished to utilize a conventional screw in order o^accomplis a simple domestic task. To overcome this problem often it was necessary to make a preliminary hole or aperture in the wood so as to enable the screw point to obtain a good "grip" before proceeding to drive the screw into the wood. Also, when driving a conventional screw into hardwood often it was necessary to coat the exterior surface of the screw with a lubricant or greasy material such as soap so as to enable the turns of the thread to obtain a better purchase on the interior surface of the bore formed by the screw within the wood. Another problem of conventional screws that was often prevalent was that when it was desired to drive the screw into a particular location that was relatively inaccessible to the user, such an operation was relatively difficult because of the flattened base wall of the screw slot. This meant 'that one had to use a very small screwdriv so as to enable the screwdriver tip to properly engage with the screw slot or operate the shank of the screwdriver at an angle to the base wall of the screw slot. This often resulted in the screw being driven in at an angle instead of in the desired straight line normal to the wood It is therefore an object of the invention to provide a fastener which alleviates the problems of conventional fasteners and which is simple to use and convenient in operation. The invention provides a threaded fastener having a head and a shank. The head has a slot having a base wall which is modified in accordance with the following discussion so as to provide a greater torque than is provided with conventional fasteners and which can be used with a greater of driving tools such as screwdriver angles than compared to conventional fasteners. DISCLOSURE OF THE INVENTION The present invention relates to a threaded fastener comprising a threaded shank and a head at one end thereof, the head including at least one slot traversing the head adapted to receive a driving tool, the or each slot having a base wall of substantially convex configuration when viewed from the head end along the longitudinal axis of the shank. Another feature " of the present invention, relates to a method of forming a threaded fastener comprising cold forming a fastener blank having a shank and a rough- formed head, punching said blank in a finishing die to simultaneously finish the head and form said slot, a roll forming said thread on the shank while removing any excess metal extruded in the slot punching step. In a further aspect of the invention there is provided an apparatus for producing the tlireaded fasteners comprising a die to support the fastener blank, a punch to cooperate wit said die to form the finished head and the slot, and a shank threader and excess metal removal means . The invention also includes within its scope a driving tool for use with a threaded fastener, the tool having a blade portion with a leading edge of complementary shape to the base of the fastener slot. The threaded fastener of the invention is preferably a screw. Preferably, the head of the fastener has an erx- ;r* ; ,^Λ7?" CM?I /,. Y Yvv'IlPr'OU S lθ face which may adopt any suitable configuration such as substantially planar or flat or alternatively being domed or most preferably countersunk. The body of the fastener head may have any convenient configuration such as cylindrical. In fact, if desired, the body of the "head" may be indistinguishable from the body of the shank each having the same diameter. In this case the threaded fastener of the invention will have a threaded shank and a head having the modified slot. Preferably, the fastener head has a slot which is formed as ' a substantially U-shaped channel traversing the head. Desirably, the slot is located in the mid- region of the head. In accordance with the invention the base wall of the slot is of substantially convex configuration when viewed from the head end along the longitudinal axis of the shank. The base wall is most desirably symmetrical having regard to the longitudinal axis of the shank. The convex base wall of the slot # may have any suitable degree of curvature. However, it is preferred when the head end has a circular periphery that the convex base wall has a surface of radius of curvature substantially equal to the diameter of the head. The peak or uppermost point of the base wall of the slot may be located only a relatively short distance from the face of the head remote from the shank when compared to the corresponding distance of the base wall of the slot in conventional fasteners. The shank of the fastener of the invention may adopt any standard configuration which is available in relation to conventional fasteners. Thus the shank may have a substantially cylindrical body or a body which converges towards its end remote from the head. The shank has a threaded portion any may also have an unthreaded portion intermediate the screw head and the threaded portion of the shank. Although the foregoing discussion has centered on the fastener of the invention having one slot, it will be appreciated that it is within the scope of the invention to have a plurality of slots located in the fastener head. At least one of these slots will have the convex base wall. In the cold forming operation for producing the shank and rough-formed head, it is preferred that the die used in the punching step be employed. The die used in the apparatus for producing the threaded fastener is preferably adapted to support a countersunk screw. The shank threader and excess metal removal means may comprise a thread rolling die having opposed operative surfaces at least one of which reciprocates relative to the other. Preferably, the operative surfaces of the die gradually converge along the longitudinal axis of the die. Each operative surface generally includes a ribbed formation to produce the desired thread on a shank and adjacent one edge of each surface, a longitudinally extending roughened bevelled surface to remove excess metal. The driving tool of the invention may include a handle portion and a blade portion with a leading edge as in conventional driving tools but wherein the leading edge has a concave con iguration. It will be appreciated that the provision of a convex configuration in the base wall of the fastener slot will provide such a fastener with a number of advantages when compared to conventional fasteners. This applies with even greater emphasis when a driving tool of the invention is also utilized. Thus the fastener may be driven into a supporting surface with greater torque than is possible with conventional fasteners. In fact a satisfactory torque can be imparted to the head of the fastener even when the longitudinal axis of the driving tool does not coincide with the longitudinal axis of the fastener. Thus in relatively inaccessible locations the fastener may be driven into the supporting surface in the desired direction (normally at right angles to the supporting surface) even when the axis of the driving tool is operated at an angle to the axis of the fastener. Also in relation to conventional fasteners there is a tendency for the tip of the driving tool to become dislodged from its mating fastener slot during use. This tendency is alleviated in the present invention because of the secure engagement provided by the mating curved C-ΛTl - - - surfaces of both the fastener and driving tool of the invention in use. BRIEF DESCRIPTION OF DRAWINGS The invention will now be described with reference to the accompanying diagrammatic drawings in which:- Fig. 1 is a perspective view of the fastener blank produced by cold forming; Fig. 2 is a perspective view of a punch and finishing die; Fig. 3 is a cross-section view along line III-III in Fig. 2; Fig. 4 is a perspective view; partially in cross-section of the fastener blank after punching; Fig. 5 is a perspective view of a thread rolling and head deburring die; Fig. 6 is a fragmentary view of a threaded fastener in accordance with an embodiment of the present invention shown as a countersunk screw. In Fig. 1 there is illustrated a fastener. lank 1 » having a cylindrical shank 2 and a rough-formed countersunk head 3. The blank 1 may be the product of cold forming a suitable length of rod or round wire from which the blank I is made in finishing die 4. Fig. 2 illustrates an enlarged punch 5 having a cylindrical body 6 and an end face 7 forming a die 7a which is capable of imparting a convex slot in the countersunk head 3. In Fig.2 and Fig. 3, the die 4 comprises a mould 8 having a countersunk recess 9 for finishing the rough- formed head 3, a cylindrical bore 10 - for receiving the shank 1 and cavities 10a which are large enough to receive both the die 7a of the punch 5 and burrs 12 formed when the convex slot 13 is formed. By engaging the punch 5 over the die 4 which contains a blank 1 and applying suitable pressure to the punch 5, the convex slot 13, burrs 12 and finishing head II o the blank 14 illustrated in Fig. 4 are simultaneously produced. The shank 2 of blank 14 of Fig. 4 is then subjected to a thread rolling die 15 of the construction shown - - - The die 15 is provided with opposed operative surfaces 19 having threaded ribs 16 and threaded grooves 16a arranged in the usual screw forming pattern. The die also contains a bevelled deburring face 17, which extends longitudinally of the die 15, having a roughened surface 18 which when in contact with the burrs 12 of blank 14 removes the burrs. When the blank 14 is subjected to the thread rolling operation, the burrs 12 on the finished head 11 simultaneously contact the roughed surface 18 and are removed by shearing. The final product obtained following the thread rolling and deburring operation is a threaded fastener of the present invention as shown in Fig. 6. Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention. ( OMPI Λ, IPO

Claims: 1. A threaded fastener comprising a threaded shank and a head at one end thereof, the head including at least one slot traversing the head adapted to receive a driving tool, the or each slot having a base wall of substantially convex configuration when viewed from the head end along the longitudinal axis of the shank. 2. A fastener according to Claim 1, wherein the head end has a circular periphery and the convex base wall has a surface of radius of curvature substantially equal to the diameter of the head. 3. A fastener according to Claim 1 wherein the shank converges towards its end remote from the head, 4. A fastener according to Claim 1 which is a countersunk screw. 5. A driving tool for use with a threaded fastener according to Claim 1 having a blade portion with a leading edge of complementary shape to the base of the fastener slot. 6. A method of forming a threaded fastener according to Claim 1 comprisin cold forming a fastener blank having a shank and a- rough-formed head, punching said blank in a , finishing die to simultaneously finish the head and form said slot, and roll forming said thread on the shank while removing any excess metal extruded in the slot punching step. 7. A method according to Claim 6, wherein the cold forming operation is performed in the same die as in the punching step. 8. An apparatus for producing the threaded fasteners by the method of Claim 7, comprising a die to support the fastener blank, a punch to cooperate with said die to form the finished head and the slot, and a shank threader and excess metal removal means. 9. An apparatus according to Claim 8 , wherein the shank threader and excess metal removal means comprises a thread rolling die having opposed operative surfaces at least one of which reciprocates relative to the other, each operative surface having a ribbed formation to produce the desired thread on the shank and a roughened bevelled surface portion adjacent one edge of each surface to remove excess metal. - S - 10. An apparatus according to Claim 7 wherein the finishing die is adapted to support a countersunk screw. OM?I

Inventors: CASTLES K
Applicants: CASTLES K
Application year: 1980
Main classification: F16B23
IPC codes: F16B23