IE51184B1

IE51184B1 - Self-drilling fasteners and flute configurations therefor

Info

Publication number: IE51184B1
Application number: IE2443/80A
Authority: IE
Original assignee: Illinois Tool Works
Priority date: 1979-11-26
Filing date: 1980-11-25
Publication date: 1986-10-29
Also published as: ES263215Y; IT8026206A0; JPS5686217A; GB2101022B; NO158554B; GB2100157A; FR2470281B1; DE3044001C2; JPS6255006B2; CH640318A5; NO158554C; CA1175688A; LU82954A1; ZA806860B; MX171209B; NL8006295A; FI803666L; NZ195635A; GB2100157B; NO803548L

Abstract

A rotary milling cutter 50, for fluting a drill screw shank, has a plurality of peripherally positioned cutting teeth 52, the outer extremity of each of said teeth 52 being formed as a semicircle 54 with a rib 56 formed thereon and each of said ribs 56 having an arcuate configuration whereby, in use, the drill screw shank is shaped to present a flute 16, 18 having at least one longitudinally-extending chip-breaking trough 46, 48.

Description

Many different self-drilling fastener, or drill screw, configurations have been developed to date. Designing drill screws has been something less than an exact science, however, with the reasons why some drill screws work well in some materials but not in others, and why other drill screws do not work well at all, remaining something of a mystery.

For example, it is known that a simple nail point when turned at a sufficient rate of speed is sufficient to penetrate some materials, dry wall for example. On the other hand, no drill screw yet devised can satisfactorily drill through some of the high-strength, low-alloy steels.

Two of the basic criteria used to judge drill screw performance are: (1) the amount of end load required for the screw to drill and (2) the time in seconds for the screw to penetrate the particular material being drilled. Obviously, in an assembly line type environment where a large nimiber of fasteners are installed by a workman in an hour's time, reduction in both the amount of end load required and drilling time will be of benefit to both the individual workman and to his employer.

In accordance with one aspect of the present invention, a self20 drilling fastener has a drilling tip at one end of a substantially cylindrical fastener shank, said tip comprising a pair of flutes extending at generally equal opposite angles with respect to the longitudinal axis of said shank and lying generally on opposite sides thereof, a pair of heel portions each presenting a heel surface extending intermediate said flutes, said heel surfaces intersecting to define a narrow chisel edge, each of said flutes intersecting with said heel surfaces to form an edge which i«an axial end view of said shank includes a straight cutting edge section extending inwardly from the periphery of said shank and a curved drag edge, or sequential cutting edge and drag edge section, having a substantially uniform radius of curvature in a plane perpendicular to the axis of said flute, wherein each of said heel portions is of substantially immediately increasing width, considered in planes parallel to the chisel edge with progressively increasing distance radially outwardly of the chisel edge, thereby buttressing said cutting edges and enhancing resistance of said tip to breaking during drilling.

Other aspects of the present invention are set out in the following claims, and indeed other claims based on the following disclosure are the subject of our patent applications nos and divided herefrom.

It has been found that self-drilling fasteners in accordance with the present invention can drill with a lower end load, and in a shorter period of time even though the end load is reduced, in comparison with conventional self-drilling fasteners, and are further capable of drilling satisfactorily high-strength, low-alloy steels, which has hitherto not been possible, because of the strong cutting edges and the narrow chisel edge in the configurations of the present self-drilling fasteners.

The self-drilling fasteners of the present invention are preferably manufactured using rotary milling cutters rather than conventional fluting and pointing saws. One of the chief benefits of using such cutters is that, unlike conventional saws, when the teeth are sharpened little or no material is removed from the diameter. Hence, the optimum flute configuration becomes more readily reproduced (i.e. there is less variance in quality due to wearing of the cutter). A further advantage, which also adds to part consistency, is that the teeth have a stronger configuration which is less subject to deflection.

In the preferred manufacture of the present self-drilling fasteners, the fluting cutters are simultaneously plunged into the shank of a screw blank along axes of movement which are parallel, but offset. The planes of rotation of the cutters are inclined at equal but opposite acute angles relatively to the axis of the blank as the cutters are moved along the parallel axes of movement. As a result, each flute cross-section has a straight section corresponding to the direction of movement of a cutter, and a curved section corresponding to the profile at the extremities of the cutter teeth.

The self-drilling fasteners may be provided with a conventional 90° or 105° point angle, or the point may be formed by cutters which each has a generally concave tooth configuration.. This will produce a generally convex-sided point, in which each heel portion.may have a uniform radius of curvature, or may be formed by a pair of planar surfaces which intersect to form an included angle of 172J°. In this latter instance the drill point will have a compound included angle which may be 105° at the tip and 90° elsewhere.

Preferably, each of said flutes includes a chip-breaking feature, namely a shallow channel or trough (possibly of arcuate configuration) extending the length of, and generally parallel to the axis of, said flute.

Several self-drilling fasteners, according to the present invention, will now be described, by way of example only, with reference to the accompanying drawings, in which:4 S1184 Figure 1 is a side elevation of a self-drilling, self-tapping screw embodying the present invention; Figure 2 is an end view taken from line 2-2 of Figure 1; Figure 3 is an enlargement of the drill point shown in Figure 2; Figure 4 is a side elevation taken perpendicularly to the chisel edge from line 4-4 of Figure 3; Figure 5 is a side elevation taken parallel to a cutting edge from line 5-5 of Figure 3; Figure 6 is a side elevation taken parallel to the chisel edge from line 6-6 of Figure 3; Figure 7 is a side elevation taken from line 7-7 of Figure 3; Figure 8 is a sectional view taken along plane 8-8 of Figure 7, a plane which is perpendicular to the axis of one of the flutes; Figure 9 is an end view of an alternative embodiment in which the cutting edges are below centre; Figure 10 is an end view of another alternative embodiment in which the cutting edges are on centre”; Figure 11 is an end view of yet another embodiment of the present invention which has a chip-breaking feature; Figure 12 is a side elevational view of the Figure 11 embodiment taken from line 12-12; Figure 13 is a sectional view taken along plane 13-13 of Figure 12 and showing the fluting cutter with which it is made; Figure 14A is a side elevational view of a 90° point angle; Figure 14B is a side elevational view of a standard 105° point angle; Figure 14C is a side elevational view of one form of a convex-sided point, also showing the tooth configuration of a cutter and forming same; and Figure 14D is a side elevational view of an alternative form of convex-sided point, each heel thereof being formed by a pair of angulated surfaces, also showing the tooth configuration of a cutter for forming this point.

A self-drilling, self-tapping fastener embodying the present invention is shown generally at 10. Figures 1 to 8 show a plurality of views of the fastener 10 in order that the configuration of the drill tip 12 can be fully appreciated. The self-tapping thread 14 may take any convenient form.

The drill tip 12 is formed using rotary milling cutters for both fluting and pointing in place of conventional saws, somewhat in the manner taught by U.S. Patent No. 3 933 075. The fluting cutters (not shown) are positioned on either side of the screw blank with their' planes of rotation at equal opposite angles (generally of the order of 15°) with respect to the axis of the blank. Unlike the technique shown in said U.S. Patent 3 933 075 where the cutters are plunged into the blank to form uniformly radiused flutes, in forming flutes 16 and 18 of the screw 10 of the present invention, the cutters are plunged into the blank in a non-radial direction so that their side edges impart a straight portion 20 and 22 (see Figure 8) respectively to each of the flutes. The feed may be somewhat similar to the feed arrangements of our British Patent Application No. 8 001 756. Each flute then has a compound configuration which includes a straight portion , 22 and a curved portion 24, 26, here of uniform radius. In the preferred embodiment these straight portions‘20, 22 include cutting edges 28 and 30 while the radiused portions 24 and 26 include trailing or drag edges 32 and 34. The central axes of the cutters are arranged so that the thinnest portion of the web will be back of point.

A chisel 36 is formed at the intersection of the surfaces of heel portions 38 and 40. Chisel 36 forms an acute angle with each of the cutting edges 28 and 30 of the order of 30° as viewed in Figure 3. The configurations of the cutting edges 28, 30 and drag edges 32, 34, as they are seen in Figures 2 and 3, are necessarily the summation 6 of the effects of the configuration of the flutes 16 and 18 and the configuration of heel portions 38 and 40. In particular, the straight portions 20 and 22 of the cutting edges 28 and 30, as viewed in Figure 3, lie parallel to a diameter of the screw 10, with said diameter intersecting neither of the flutes 16 and 18. In this arrangement the cutting edges and 30 are said to be above centre.

In order to show the actual configuration of the flute absent the effects of the point, Figure 8 depicts a cross-section taken along plane 8-8 of Figure 7, a plane which is perpendicular to the axis of flute 16. Flat surface 20, at this section, is past or beyond said above-mentioned diameter, which is parallel to the two cutting edges 28 and 30. This is due to the inclination of the flutes 16 and 18 relatively to the longitudinal axis of the screw. The radiused portion 24 has a uniform radius of curvature in this plane corresponding to the radius of the profile of cutting teeth of the cutter which formed it. Plane 8-8 is, of course, not perpendicular to the axis of the flute 18 but is, rather, sloped at a 30° angle relative thereto.

Another feature of the flute configuration is shown in Figure 6. The intersection of the rotary milling cutters with the cylindrical periphery of the shank results in curved leading edges 42 and 44 of the flutes 16 and 18. This, in conjunction with the circular configuration of the cutters, produces a scoop-like configuration in the vicinity of each of the cutting edges 28 and 30. This scoop shape may result in the drill screw pulling itself into the drilled hole, thereby at least partially accounting for the drill screw's advantageous drilling capabilities.

It will be appreciated, from a study of the accompanying Figures 1 to 8, that each of said heel portions 38 and 40 is of substantially immediately increasing width, considered in planes parallel to the chisel edge 36 with progressively increasing distance radially outwardly of the chisel edge 36, thereby buttressing said cutting edges 28 and 30 and enhancing resistance of said tip 12 to breaking during drilling.

The included angle of each of said cutting edges 28 and 30 defined by said flutes and said heel surfaces varies over the length of said cutting edge with the most acute value of that angle occurring at the outer edge of said shank, thereby presenting sharply relieved cutting edges 28 and 30 to a workpiece. Each of said heel surfaces further intersects a portion of the outer surface of said shank to form an arcuate edge, with each of said heel surfaces lying entirely on one side of a plane containing said chisel edge 36 and a respective one of said arcuate edges, and with each of said straight sections 20 and 22 of said cutting edges 28 and 30 being non-linear in a plane which contains said straight section and is parallel to the longitudinal axis of said shank.

Although Figures 1 to 8 depict a configuration in which the cutting edges are above centre, as explained hereinbefore, it will be appreciated that by decreasing the depth of the cutters' plunge (in the left/right direction of Figure 3), and moving the cutters laterally (in the up/down direction of Figure 3), both a below centre and an on centre condition can be achieved. These alternate configurations are depicted in Figures 9 and 10, respectively. More particularly, Figure 9 shows an arrangement in which the straight portions of the cutting edges lie parallel to the diameter of the drill screw, with said diameter intersecting both of the flutes, whereas Figure 10 shows an arrangement in which the straight portions of the cutting edges actually lie along a diameter of the drill screw. In these arrangements, the curved portions 32 and 34 of the flutes include part of the cutting edges 28 and 30 thereby giving the cutting edges a compound configuration. Particularly for these alternative arrangement, it is important to maintain a relatively short chisel length in order to ensure that merely a low end load is needed to initiate drilling.

To date, chip-breaking features have only been added to forgedpoint drill screws. In the embodiment of the present invention shown in Figures 11 to 13, however, shallow troughs 46 and 48 extend longitudinally in each milled flute 16 and 18. This chip-breaking feature is milled by a cutter 50 which has a plurality of teeth 52 (preferably a 20 and 32 tooth cutter is used). Each tooth 52 has a cutting edge at its outer periphery formed as a uniform first radiused portion 54 (such as a semicircle) and an arcuate rib 56 having a second shorter radius. The rib 56 may be offset from the central plane of the cutter one direction or the other depending on the flute configuration desired i.e. the position of the trough within the flute relatively to the position of the chisel edge. Although only the above centre configuration has been shown in Figure 11, it will be appreciated that the chip-breaking troughs could also be added to the below centre and on centre configurations depicted in Figures 9 and 10.

As previously mentioned, the end view of the drill screw 10 (as shown in Figures 3, 9, 10) and the performance of the drill screw 10 will vary depending on the particular point added to the blank. Thus, it may be that one point will out-perform another in a first material but not in a second material. However, preliminary testing indicates that the convexsided point depicted in Figures 1 to 8 and also shown in Figure 14C consistently out-performs other point geometries when combined with the flute configuration previously discussed. To form this convex-sided 184 point, a first cutter (not shown) having concave teeth is used to remove a generally triangular portion of the blank following fluting to form heel region 40 and then a second cutter 58 with concave teeth 60 forms heel portion 38 and chisel 36.

An alternative generally convex-sided point is shown in Figure 14D. In this embodiment each of the heel portions includes a pair of planar surfaces 62 and 64 which form an obtuse included angle. The generally convex-sided point of this embodiment is, again, formed by two cutters (one of which is shown at 66) but here teeth'68 have a periphery formed as two angular portions 70 and 72. These angular portions define an obtuse angle 0 which is generally equal to the angle to be formed on the drill screw. Preferably both of these obtuse angles equal 172J° (as measured internally on the drill screw and externally on the cutter). In this manner, the point formed by surfaces 62 will have an included angle which is 15° greater than that formed by planar surfaces 64, 105° as opposed to 90°, for example.

A Of course conventional single angle drill points such as 90. (Figure 14A) and 105° (Figure 14B) can be used on the present drill screw as well and may prove advantageous for certain applications.

Various changes, modifications and variations will become apparent to persons of ordinary skill in the art in view of the foregoing disclosure. For example, the convex-sided point of Figure 14C could have a lesser or greater included angle by shifting the axis of the cutter 58 with respect to the axis of the blank. Further, it is conceivable that the present self-drilling fasteners could be formed by forging.

S1184 In the following claims, a self-drilling fastener stated to be “as hereinbefore defined means a self-drilling fastener having a drilling tip at one end of a substantially cylindrical fastener shank, said tip comprising a pair of flutes extending at generally equal opposite angles with respect to the longitudinal axis of said shank and lying generally on opposite sides thereof, a pair of heel portions each presenting a heel surface extending intermediate said flutes, said heel surfaces intersecting to define a narrow chisel edge, each of said flutes intersecting with said heel surfaces to form an edge which in an axial end view of said shank includes a straight cutting edge section extending inwardly from the periphery of said shank and a curved drag edge, or sequential cutting edge and drag edge, section, having a substantially uniform radius of curvature in a plane perpendicular to the axis of said flute.

Claims

1. A self-drilling fastener as hereinbefore defined wherein each of said heel portions is of substantially immediately increasing width, considered in planes parallel to the chisel edge With progressively increasing distance radially outwardly of the chisel edge, thereby buttressing said cutting edges and enhancing resistance of said tip to breaking during drilling.

2. A self-drilling fastener as hereinbefore defined, or in accordance with claim 1, wherein the included angle of each of said cutting edges defined by said flutes and said heel surfaces varies over the length of said cutting edge with the most acute value of that angle occurring at the outer edge of said shank, thereby presenting sharply relieved cutting edges to a workpiece.

3. A self-drilling fastener as hereinbefore defined, or in according with either claim 1 or claim 2, wherein each of said heel surfaces further intersects a portion of the outer surface of said shank to form an arcuate edge, with each of said heel surfaces lying entirely on one side of a plane containing said chisel edge and a respective one of said arcuate edges, and with each of said straight sections of said cutting edges being non-linear in a plane which contains said straight section and is parallel to the longitudinal axis of said shank.

4. A self-drilling fastener according to claim 1 or claim 2, wherein the included angle between said two heel portions at their intersection is 90°.

5. A self-drilling fastener according to claim 1 or claim 2, wherein the included angle between said two heel portions at their intersection is 105°. 81184

6. A self-drilling fastener according to claim 3, wherein said non-linearity results from each of said cutting edges being convex.

7. A self-drilling fastener according to claim 3, wherein said non-linearity results from each of said cutting edges comprising a plurality of linear segments.

8. A self-drilling fastener according to claim 7, wherein each of said two heel portions comprises two generally planar surfaces, with the pair of said planar surfaces adjacent said chisel edge having an included angle of 105° while the pair of said planar surfaces adjacent said shank have an included angle of 90°.

9. A self-drilling fastener according to any preceding claim wherein, for each of said flutes, said curved section includes a portion of said cutting edge.

10. A self-drilling fastener according to any one of claims 1 to 9, wherein said straight sections of said cutting edges, as viewed along the fastener axis, lie along a diameter of said fastener.

11. A self-drilling fastener according to any one of claims 1 to 9, wherein said straight sections of said cutting edges, as viewed along the fastener axis, He parallel to a diameter of said fastener, with said diameter intersecting both of said flutes.

12. A self-drilling fastener according to any one of claims 1 to 9, wherein said straight sections of said cutting edges, as viewed along the fastener axis, lie parallel to a diameter of said fastener, with said diameter intersecting neither of said flutes. '51184

13. A self-drilling fastener according to any preceding claim, wherein each of said flutes includes a chip-breaking feature.

14. A self-drilling fastener according to claim 13, wherein each of said chip-breaking features comprises a shallow channel 5 extending the length of, and generally paralled to the axis of, said flute.

15. A self-drilling fastener substantially as hereinbefore described with reference to Figures 1 to 8, Figure 9, Figure 10, Figures 11 to 13, or those Figures as modified by any one of 10 Figures 14A to 14D, of the accompanying.drawings.