GB2221004A

GB2221004A - Tamperproof fastener, punch and driving tool

Info

Publication number: GB2221004A
Application number: GB8817356A
Authority: GB
Inventors: Melvyn Douglas Jackson
Original assignee: EUROP IND SERVICES Ltd
Current assignee: EUROP IND SERVICES Ltd
Priority date: 1988-07-21
Filing date: 1988-07-21
Publication date: 1990-01-24
Also published as: GB8817356D0

Abstract

A tamperproof threaded metal fastener has its head 11 provided with a recess comprising a central cavity 12 and preferably three grooves 13 extending radially outwardly from the cavity, spaced symmetrically therearound. The end walls 17 of the grooves lie on a conical or pyramidal surface coaxial with the axis of the fastener and having an included angle at its vertex within the range 40 DEG to 55 DEG , preferably 43 DEG . The invention also provides a driver for the fastener, and a punch Fig 4, for making such a recess. V-shaped valleys 18 may also be punched. <IMAGE>

Description

TAMPERPROOF FASTENER, PUNCH AND DRIVING TOOL This invention relates to threaded fasteners, such as screws or bolts, having a driving recess formed in the head of the fastener which recess is of a non-standard form preventing driving engagement by a conventional configuration of screw driver blade or bit. The invention also relates to a punch for forming such a recess in the head of a fastener and also relates to a driving tool for engagement within such a recess.

Fasteners with non-standard driving recesses in their heads are hereinafter referred to as tamperproof fasteners. Tamperproof fasteners are intended for use, for example, in the assembly of electrical equipment where it is required to prevent unauthorised access to parts of such equipment. Such tamperproof fasteners do however have to be capable of good torque transmitting engagement by non-standard cooperating driving tools for automatic assembly purposes and to be capable of being unscrewed by use of a cooperating driving tool for subsequent service or repair purposes by authorised personnel.

Known tamperproof fasteners have included, for example, a fastener wherein the driving recess in the head comprises three equiangularly spaced slots extending outwardly of a central cavity in the fastener head, the central longitudinal axis of each of which slots lies in a plane which does not intersect the longitudinal axis of the fastener. That is to say, although one side wall of each such slot may lie in a plane which is truly radial of the central axis of the recess, the other opposed parallel side wall of the slot is offsetfrom such radial plane.

Another known type of tamperproof fastener has a driving recess in its head comprising three equiangularly spaced slots extending radially of a central cavity in the fastener head, the opposed side walls of each slot being curvilinear to provide, between each adjacent pair of slots, a semi-cylindrical wall portion within the recess.

It is an object of the present invention to provide an improved tamperproof fastener, punch and driving tool wherein the driving recess in the fastener head is particularly suited to good torque transmitting engagement by automatic driving tools.

In accordance with one aspect of the invention there is provided a tamperproof threaded metal fastener having a driving tool engaging recess formed in a head of the fastener, said recess comprising a central cavity and three, or any odd number in excess of three, grooves extending radially outwardly of said cavity and spaced symmetrically therearound, each groove having a pair of opposed substantially parallel side walls within each of which is receivable a radially outwardly projecting correspondingly shaped portion of a driving tool received within the recess; each groove opening at an inner end thereof into the central cavity and having an end wall at an outer end which is inclined downwardly and inwardly from said outer end towards said inner end, said end walls of the grooves lying on a conical or pyramidal surface coaxial with the central longitudinally extending axis of the fastener wherein the included angle at the vertex of such conical or pyramidal surface has a value lying within the range 40 to 55 .

Also in accordance with the invention there is provided a driving tool for use with a tamperproof fastener as described in the preceding paragraph, such tool having a nose with radially extending wings adapted to engage in and substantially conform to the shape of the grooves, the included angle at the vertex of a cone or pyramid containing the radially outer surfaces of the wings having a value lying within the range 40 to 55 .

Also in accordance with the invention there is provided a punch for forming a recess in the head of a tamperproof fastener of the type described above, such punch comprising a nose to form the said cavity of the recess and ribs extending radially of the nose to form said grooves, the included angle at the vertex of a cone or pyramid containing the radially outer surfaces of the ribs having a value lying within the range 40 to 55 .

Preferably the central cavity of the recess in the fastener is formed with V shaped valleys in the walls thereof intermediate each pair of circumferentially adjacent grooves, one such valley being located in diametrically opposed relation to each of said grooves and, conveniently, three such grooves are formed in the recess. Preferably the said included angle of the recess has a value in the range 40"-45", conveniently 43 .

For use with a fastener as described in the preceding paragraph, there are provided three said wings extending radially outwardly of the nose of the driving tool with the said included angle having a value of 43 .

A punch for forming such a recess in the head of a fastener will be provided with three said ribs extending radially outwardly of the nose of the punch with the said included angle being 43 .

Preferably the punch includes a cavity for forming the head of the fastener, said nose and ribs of the punch projecting axially and centrally of the base of the punch cavity to form a said recess in the fastener head.

The punch nose is conveniently provided at positions intermediate each of said punch ribs with additional ribs of V form each having an outer edge which is inclined downwardly and inwardly towards the punch axis.

When such a punch is used to punch the recess in the head of a fastener, the metal displaced by the formation of the V-section valleys inhibits metal fall-away from the punch intermediate the recess grooves and along the groove side walls so that the recess conforms closely to the configuration of the punch.

The punch may have a plurality of projections located at positions spaced equiangularly around and intermediate each of said ribs, said projections being adapted during punching of the fastener recess to engage with the metal forming the upper end face of the fastener head at positions intermediate each of said recess grooves to cause displacement of metal in the fastener head adjacent the end face thereof towards each of said adjacent groove forming punch ribs so as to inhibit fall-away of fastener head metal from the side faces of said punch ribs during the formation of the recess by the punch.

Each of said punch projections conveniently comprises a projecting ridge provided on a punch body portion adjacent its junction with the nose at positions spaced equidistantly between the punch ribs with each ridge extending radially in relation to the punch axis and being adapted as the punch penetrates fully into the fastener head to indent the end face of the metal of the head at positions intermediate the recess grooves and displace metal at the end face of the head towards said grooves.

During the operation of punching the recess in the tamperproof fastener by a punch as described in the preceding two paragraphs, the metal of the end face of the fastener is indented in the direction of the fastener axis at a position intermediate each circumferentially adjacent pair of side walls of each circumferentially adjacent pair of grooves, each indentation being disposed between the outer periphery of the end face of the fastener and the upper edge of those walls of the central cavity of the recess which are intermediate circumferentially adjacent grooves, each indentation having a depth in a direction parallel to the fastener axis which is less than such depth of said grooves but such that the metal adjacent said end face is displaced by said indenting in a direction towards the adjacent side walls of said grooves to resist the natural tendency for the metal along said side walls to fall away from the corresponding faces of the groove forming ribs of the recess forming punch during the punching of the recess, so that at least at such groove side walls, the recess conforms closely throughout the depth of said groove side walls from the recess mouth to the recess bottom with the design configuration of the recess forming punch.

When the punch has the additional ribs of V form, each of such additional ribs, at its upper end, may merge into a downwardly projecting ridge provided on a punch body portion adjacent its junction with the nose at positions spaced equidistantly between the punch ribs, with each ridge extending radially in relation to the punch axis and being adapted as the punch penetrates fully into the fastener head to indent the end face of the metal of the head at positions intermediate said recess grooves and displace metal at the end face of the head towards said grooves. The said ridges may be of generally triangular form in cross section.

During the operation of punching the recess by such a punch, the metal of the end face of the fastener is indented in the direction of the fastener axis at a position intermediate each circumferentially adjacent pair of side walls of each circumferentially adjacent pair of recess grooves and the recess adjacent its central cavity at a position between each circumferentially adjacent pair of grooves is formed with a valley of generally V shaped configuration in cross section so as to embody a pair of mutually transverse side walls intersecting on a line inclined downwardly and inwardly with respect to the fastener axis, each indentation being disposed between the outer periphery of the end face of the fastener and the upper edge of the V shaped valleys, each indentation having a depth in a direction parallel to the fastener axis which is less than such depth of said grooves, the metal displaced by the formation of each V section valley and by the formation of said end face indentations being displaced in opposite circumferential directions so as to inhibit metal fall-away from the recess forming punch respectively at positions intermediate the recess grooves and along the groove side walls so that the recess conforms closely to the design configuration of the recess forming punch.

The said indentations preferably each comprise an elongated depression which at positions intermediate said grooves extends outwardly along the end face of the fastener from the central cavity towards the periphery of said end face. Said depressions may extend radially in relation to the fastener axis and are spaced symmetrically between each circumferentially adjacent pair of grooves, each depression being of V form in transverse section with the depressions at their inner ends nearest to the central cavity of the recess each merging with a V section valley.

For use with such a tamperproof fastener the driving tool nose at positions intermediate each pair of circumferentially adjacent wings is conveniently formed with an outwardly extending rib of V form, the cross section of which decreases in a downward direction towards the end of the nose.

Other features of the invention will become apparent from the following description given herein solely by way of example with reference to the accompanying drawings wherein: Figure 1 is a top plan view of the recessed head of a tamperproof fastener formed in accordance with the invention; Figure 2 is a side elevation of the fastener head of Figure 1; Figure 3 is a side elevation of a driving tool for the fastener, positioned in relation to the fastener; Figure 4 is a side elevation of a punch for forming the recess in the fastener head; Figure 5 is an end view of the punch; Figure 6 is a perspective view of the punch.

Figure 7 is a top plan view of the recessed head of a further embodiment of fastener according to the invention.

Referring firstly to Figures 1 and 2 of the drawings, there is shown a tamperproof fastener in accordance with the invention, having a shank 10 and head 11. The head is of countersunk form, but it is to be appreciated that the invention is applicable to fasteners with heads of other configurations, e.g. those known as pan heads, round heads, cheese heads or any other conventional head. The fastener is provided in its head with a recess engagable by a driving tool, the recess comprising a central cavity 12 and three, or any odd number in excess of three, grooves 13 extending radially outwardly of the cavity and spaced symmetrically therearound. In this specific embodiment, three such grooves are provided, each having a medial plane 14 extending radially of the central cavity and which planes intersect one another at the central longitudinal axis 15 of the fastener.The planes 14 are therefore equally angularly disposed about the central axis 15, with an angle of 1200 between each adjacent pair of such planes.

Each groove 13 has a pair of opposed substantially parallel side walls 16 for receiving therebetween a radially outwardly projecting correspondingly shaped wing of a driving tool to be described hereafter. Each groove opens at its radially innermost end into the central cavity 12, and has an end wall 17 at its radially outermost end which is inclined downwardly and inwardly from its outermost end towards its innermost end. The end walls of the grooves lie on a conical or pyramidal surface coaxial with the central axis 15 of the fastener, and the included angle at the vertex of such conical or pyramidal surface has a value which lies within the range 40 to 55" and is preferably 43 .

The central cavity 12 of the recess is formed with V-shaped valleys 18 in the walls thereof intermediate each pair of circumferentially adjacent grooves and, as will be seen from Figure 1, such a V-shaped valley 18 is located in diametrically opposed relation to each of the grooves.

A driving tool for engagement with the fastener head recess shown in Figures 1 and 2 is shown in Figure 3.

The driving tool comprises a nose 20 with radially extending wings 21 adapted to engage in and substantially conform to the shape of the recess grooves 13. In the embodiment illustrated, there are three such wings 21 but it will be appreciated that if the recess in the fastener head were to have a greater number of grooves, the driving tool would have a corresponding number of wings.

The radially outermost surfaces of the wings lie on a cone or pyramid whose vertex angle lies within the range 40 to 55 , preferably 43 . Between each pair of circumferentially adjacent wings 21, the driving tool nose is provided with a respective outwardly extending rib of V form, of decreasing cross-section downwardly towards the end of the nose of the driving tool, whereby each such rib may engage in a valley 18 in the fastener head recess.

Figures 4, 5 and 6 show a punch for forming the head of the fastener. The punch comprises a block 25 of metal with a flat end face 24 from which a nose 26 projects axially and centrally for forming the recess. The nose comprises three ribs 27 extending radially outwardly and of a shape corresponding to and adapted to form the grooves 13 in the fastener recess, the ribs 27 being equally circumferentially spaced about the central axis of the punch so that an angle of 1200 is included between the central planes of each adjacent pair of ribs. The outer surfaces of the ribs, which form the end walls 17 of the grooves in the fastener recess, lie on a cone or pyramid whose vertex angle is in the range 40 to 55" and is preferably 43 .

Between each adjacent pair of ribs 27, the punch nose has a respective additional rib 28 of V form, for forming the V-shaped valleys 18 in the fastener recess.

Each such additional rib has an outer edge inclined inwardly and downwardly towards the punch axis.

The extreme end of the nose portion of the punch, beyond the ribs 27 and additional ribs 28, comprises a shallow cone 29 which forms the extreme base of the recess in the fastener head.

During the operation of punching the recess in the fastener, the metal displaced by the additional ribs 28 to form the V-shaped valleys 18 in the recess inhibits metal fall-away from the recess-forming punch at the main ribs 27 thereof, so that the recess conforms closely to the configuration of the punch.

The punch shown is for forming the recess in the fastener illustrated, which has a countersunk head. Thus the block 25 has the flat end surface 24 from which the nose projects. A punch to form the recess in a fastener head of one of the other types above referred to, e.g.

round head or pan head, would have its nose projecting from a cavity in the end of the block, the cavity being of a shape corresponding to the shape of the fastener head.

Referring now to Figure 7 of the drawings, this shows, in a view corresponding to Figure 1, the head of a fastener having a recess which has the features of the recess of Figure 1, namely a central cavity 32 and three grooves 33 extending radially outwardly therefrom and spaced symmetrically therearound. The grooves are configured as the embodiment of Figure 1, and in like manner have V shaped valleys 38 between them.

Between each circumferentially adjacent pair of grooves 33, the end face of the fastener head is provided with three indentations 39, each extending radially outwardly from the top of a respective valley 38. Each such indentation 39 has a depth in a direction parallel to the axis of the fastener which is less that the depth of the grooves.

To form the head of a fastener as shown in Figure 7, a punch generally the same as that above described with reference to Figures 4 to 6 would be used, with the additional feature that the punch would be provided with projections to form the indentations 39 in the end face of the fastener head. Such projections, as shown in broken lines at 30 in Figure 6, extend axially from the end face 24 of the punch body block 25 and radially thereon, angularly spaced mid-way between each adjacent pair of ribs 27. At its radially innermost end, each projection 30 merges into the respective additional rib 28.

During the operation of punching the recess by the punch, the metal of the end face of the fastener is indented in the direction of the fastener axis by the projections 39 at a position intermediate each circumferentially adjacent pair of side walls of each circumferentially adjacent pair of grooves 33.The indentations so formed have a depth in a direction parallel to the axis of the fastener such that the metal adjacent the end face of the fastener head is displaced by the indenting, in a direction towards the adjacent side walls of the grooves, to resist the natural tendency for the metal along the side walls to fall away from the corresponding faces of the groove-forming ribs of the punch during the punching operation The metal displaced by the formation of each V section valley between the grooves, is also displaced in opposite circumferential directions so as to inhibit metal fall-away from the punch at positions intermediate the recess grooves and along the groove side walls, so that the recess conforms closely to the configuration of the punch.

Thus, in accordance with the invention, there is provided a tamperproof fastener, driving tool therefor, and punch, wherein the recess is of a non-standard form for preventing unauthorised access by use of a conventional type of screwdriver blade or bit. The specific configuration of recess ensures the availability of good torque transmitting engagement by automatic driving tools, without damage to the fastener head.

Claims

1. A tamperproof threaded metal fastener having a driving tool engaging recess formed in a head of the fastener, said recess comprising a central cavity and three, or any odd number in excess of three, grooves extending radially outwardly of said cavity and spaced symmetrically therearound, each groove having a pair of opposed substantially parallel side walls within each of which is receivable a radially outwardly projecting correspondingly shaped portion of a driving tool received within the recess; each groove opening at an inner end thereof into the central cavity and having an end wall at an outer end which is inclined downwardly and inwardly from said outer end towards said inner end, said end walls of the grooves lying on a conical or pyramidal surface coaxial with the central longitudinally extending axis of the fastener wherein the included angle at the vertex of such conical or pyramidal surface has a value lying within the range 40 to 55".

2. A tamperproof fastener as claimed in Claim 1 wherein the central cavity of the recess is formed with V shaped valleys in the walls thereof intermediate each pair of circumferentially adjacent grooves.

3. A tamperproof fastener as claimed in Claim 2 wherein a said V shaped valley is located in diametrically opposed relation to each of said grooves.

4. A tamperproof fastener as claimed in any one of Claims 1 to 3 wherein three said grooves are formed in the recess.

5. A tamperproof fastener as claimed in any one of Claims 1 to 4 wherein the said included angle of the recess has a value of 43 .

6. A tamperproof fastener constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

7. For use with a tamperproof fastener as claimed in any one of Claims 1 to 6 a driving tool having a nose with radially extending wings adapted to engage in and substantially conform to the shape of the grooves, the included angle at the vertex of a cone or pyramid containing the radially outer surfaces of the wings having a value lying within the range 40 to 55 .

8. A driving tool as claimed in Claim 7 for use with a tamperproof fastener as claimed in Claims 4 and 5 wherein three said wings extend radially outwardly of the nose of the tool and the said included angle has a value of 43 .

9. A driving tool for use with a tamperproof fastener as claimed in any one of Claims 1 to 6 constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

10. A punch for forming a recess in the head of a tamperproof fastener as claimed in any one of Claims 1 to 6 comprising a nose to form the said cavity of the recess and ribs extending radially of the nose to form said grooves, the included angle at the vertex of a cone or pyramid containing the radially outer surfaces of the ribs having a value lying within the range 40 to 55 .

11. A punch as claimed in Claim 10 for forming a recess in the head of a tamperproof fastener as claimed in Claims 4 and 5 wherein three said ribs extend radially outwardly of the nose of the punch and the said included angle is 43 .

12. A punch as claimed in either one of Claims 10 or 11 including a cavity for forming the head of the fastener, said nose and ribs of the punch projecting axially and centrally of the base of the punch cavity to form a said recess in the fastener head.

13. A punch as claimed in any one of Claims 10 to 12, for forming a recess in the head of a tamperproof fastener as claimed in either of Claims 2 and 3, wherein the punch nose is provided at positions intermediate each pair of said punch ribs with additional ribs of V form each having an outer edge which is inclined downwardly and inwardly towards the punch axis.

14. A punch for forming a recess in the head of a tamperproof fastener as claimed in any one of Claims 1 to 6 constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

15. A punch as claimed in any one of Claims 10 to 14 comprising a plurality of projections located at positions spaced equiangularly around and intermediate each of said ribs, said projections being adapted during punching of the fastener recess to engage with the metal forming the upper end face of the fastener head at positions intermediate each of said recess grooves to cause displacement of metal in the fastener head adjacent the end face thereof towards each of said adjacent groove forming punch ribs so as to inhibit fall-away of fastener head metal from the side faces of said punch ribs during the formation of the recess by the punch.

16. A punch as claimed in Claim 15 wherein each of said punch projections comprises a projecting ridge provided on a punch body portion adjacent its junction with the ose at positions spaced equidistantly between the punch ribs with each ridge extending radially in relation to the punch axis and being adapted as the punch penetrates fully into the fastener head to indent the end face of the metal of the head at positions intermediate the recess grooves and displace metal at the end face of the head towards said grooves.

17. A punch as claimed in Claim 13, wherein each said additional rib at its upper end merges into a downwardly projecting ridge provided on a punch body portion adjacent its junction with the nose at positions spaced equidistantly between the punch ribs, with each ridge extending radially in relation to the punch axis and being adapted as the punch penetrates fully into the fastener head to indent the end face of the metal of the head at positions intermediate said recess grooves and displace metal at the end face of the head towards said grooves.

18. A punch as claimed in Claim 17 wherein said ridges are of generally triangular form in cross section.

19. A tamperproof fastener as claimed in any one of Claims 1 to 6 having a recess in the head thereof produced by a punch as claimed in any one of Claims 10 to 18 wherein, during the operation of punching the recess by the punch, the metal of the end face of the fastener is indented in the direction of the fastener axis at a position intermediate each circumferentially adjacent pair of side walls on each circumferentially adjacent pair of grooves, each indentation being disposed between the outer periphery of the end face of the fastener and the upper edge of those walls of the central cavity of the recess which are intermediate circumferentially adjacent grooves, each indentation having a depth in a direction parallel to the fastener axis which is less than such depth of said grooves but such that the metal adjacent said end face is displaced by said indenting in a direction towards the adjacent side walls of said grooves to resist the natural tendency for the metal along said side walls to fall away from the corresponding faces of the groove forming ribs of the recess forming punch during the punching of the recess, so that at least at such groove side walls, the recess conforms closely throughout the depth of said groove side walls from the recess mouth to the recess bottom with the design configuration of the recess forming punch.

20. A tamperproof fastener as claimed in any one of Claims 1 to 6 having a recess in the head thereof produced by a punch as claimed in any one of Claims 10 to 18 wherein, during the operation of punching the recess by the punch, the metal of the end face of the fastener is indented in the direction of the fastener axis at a position intermediate each circumferentially adjacent pair of side walls of each circumferentially adjacent pair of recess grooves and wherein the recess adjacent its central cavity at a position between each circumferentially adjacent pair of grooves is formed with a valley of generally V shaped configuration in cross section so as to embody a pair of mutually transverse side walls intersecting on a line inclined downwardly and inwardly with respect to the fastener axis, each indentation being disposed between the outer periphery of the end face of the fastener and the upper edge of the V shaped valleys, each indentation having a depth in a direction parallel to the fastener axis which is less than such depth of said grooves, the metal displaced by the formation of each V section valley and by the formation of said end face indentations being displaced in opposite circumferential directions so as to inhibit metal fall-away from the recess forming punch respectively at positions intermediate the recess grooves and along the groove side walls so that the recess conforms closely to the design configuration of the recess forming punch.

21. A tamperproof fastener as claimed in either one of Claims 19 or 20 wherein the indentations each comprise an elongated depression which at positions intermediate said grooves extends outwardly along the end face of the fastener from the central cavity towards the periphery of said end face.

22. A tamperproof fastener as claimed in Claim 21 wherein said depressions extend radially in relation to the fastener axis and are spaced symmetrically between each circumferentially adjacent pair of grooves, each depression being of V form in transverse section.

23. A tamperproof fastener as claimed in Claim 22 wherein the elongated depressions at their inner ends nearest to the central cavity of the recess each merge with a V section valley.

24. For use with a tamperproof fastener as claimed in any one of Claims 19 to 23 a driving tool as claimed in any one of Claims 7 to 9 wherein the nose at positions intermediate each pair of circumferentially adjacent wings is formed with an outwardly extending rib of V form, the cross section of which decreases in a downward direction towards the end of the nose.