GB2063731A

GB2063731A - Self-drilling fasteners

Info

Publication number: GB2063731A
Application number: GB8037945A
Authority: GB
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 1979-11-26
Filing date: 1980-11-26
Publication date: 1981-06-10
Also published as: PT72081B; DE3044001C2; DK151590C; GB2100157A; IT8026206A0; GB2101022B; GB2063731B; NO803548L; ATA572880A; BE886331A; SE8007945L; AU6422080A; ZA806860B; DK502480A; JPS6255006B2; MX152777A; AU539311B2; AR224552A1; FR2470281B1; GB2101022A

Abstract

A self-drilling and self-tapping screw has a compound flute configuration. Each flute (16, 18) has, in cross-section, a straight portion (28, 30) including at least part of the cutting edge and a curved portion (32, 34) defining the drag edge. The screw has a convex point configuration produced by a profiled toothed milling cutter (66) having uniformly radiused heels or, alternatively, heels which are formed by two planar surfaces (62, 64) intersecting to enclose an obtuse angle less than 180 DEG . Fluting milling cutters are introduced by movement not radial to produce the straight portions of the flutes the flutes being at an angle to the screw axis. Special milling cutters with arcuate portions and ribs formed by teeth produce chip breaking grooves int the flutes. <IMAGE>

Description

SPECIFICATION Self-drilling fasteners Many different self-drilling fastener, or drill screw, configurations have been developed to date. Designing of these drill screws has been something less than an exact science, 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 number 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 the present invention, a self-drilling fastener has a shank and a drilling tip at one end of said shank, said tip including a pair of flutes lying on opposite sides of said fastener and extending at equal opposite angles with respect to the axis of said fastener, a pair of heel portions extending intermediate said flutes, said heel portions intersecting to define a narrow chisel point, each of said flutes defining with said heel portions a cutting edge and a drag edge, and each of said flutes having a compound configuration, as viewed along the flute axis, formed by a straight section extending inwardly from the outer edge of said shank and including at least a portion of said cutting edge, and a curved section including at least said drag edge.

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 selfdrilling 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 point in the configuration of the present self-drilling fasteners.

These advantages of the present invention are much enhanced when, for each of said flutes, said curved section has a substantially uniform radius of curvature in a plane perpendicular to the flute axis.

In some embodiments of the present invention, for each of said flutes, said curved section includes a portion of said cutting edge.

The drill screw of the present invention is preferably manufactured using rotary milling cutters rather than the 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 drill screws, 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 drill screw may be provided with a conventional 90 or 105 point angle, or the point may be formed by cutters which have a generally concave tooth configuration. This will produce a generally convex 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 1722 . 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: 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 Fig. 1; Figure 3 is an enlargement of the drill point shown in Fig. 2; Figure 4 is a side elevation taken perpendicular to the chisel edge from line 4-4 of Fig.

3; Figure 5 is a side elevation taken parallel to a cutting edge from line 5-5 of Fig. 3; Figure 6 is a side elevation taken parallel to the chisel edge from line 6-6 of Fig. 3; Figure 7 is a side elevation taken from line 7-7 of Fig. 3; Figure 8 is a sectional view taken along plane 8-8 of Fig. 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 ii 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 Fig. 11 embodiment taken from line 12-12;; Figure 13 is a sectional view taken along plane 13-13 of Fig. 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 generally convex point, also showing the tooth configuration of a cutter for forming same; and Figure 14D is a side elevational view of an alternative form of generally convex 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. Figs. 1-8 show a plurality of views of the fastener 10 in order that the configuration of the drill tip 1 2 can be fully appreciated.

The self-tapping thread 14 may take any convenient form.

The drill tip 1 2 is formed using rotary milling cutters for both fluting and pointing in place of the conventional saws, somewhat in the manner taught by U.S. Patent 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 1 6 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 Fig. 8) respectively to each of the flutes.The feed may be somewhat similar to the feed arrangements of our co-pending British Patent Application No. 8001 756. Each flute then has a compound configuration which includes a straight portion 20, 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 by the intersection 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 Fig.

3. The configurations of the cutting edges 28, 30 and drag edges 32, 34, as they are seen in Figs. 2 and 3, are necessarily the summation of the effects of the configuration of the flutes 1 6 and 1 8 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 Fig. 3, lie parallel to a diameter of the screw 1 0, with said diameter intersecting neither of the flutes 1 6 and 1 8. In this arrangement the cutting edges 28 and 30 are said to be "above centre".

In order to show the actual configuration of the flute absent the effects of the point, Fig. 8 depicts a cross-section taken along plane 8-8 of Fig. 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 1 6 and 1 8 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 1 8 but is, rather, sloped at a 30 angle relative thereto.

Another feature of the flute configuration is shown in Fig. 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 1 6 and 1 8. 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 screws advantageous drilling capabilities.

Although the preferred embodiment depicts 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 Fig. 3), and moving the cutters laterally (in the up/down direction of Fig. 3), both a "below centre and an "on centre" condition can be achieved. These alternate configurations are depicted in Figs. 9 and 10, respectively. More particularly, Fig. 9 shows an arrangement in which the straight portions of the cutting edges lie parallel to a diameter of the drill screw, with said diameter intersect ing both of the flutes, whereas Fig. 10 shows an arrangement in which the straight portions of the cutting edges actually lie along a diameter of the drill screw.In these embodiments, 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 embodiments, 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.

Figs. 11 to 1 3 depict yet another aspect of the present invention. To date, chip-breaking features have only been added to forged-point drill screws. In the embodiment of the present invention shown in Figs. 11 to 13, however, shaow troughs 46 and 48 extend longitudinally in each milled flute 1 6 and 1 8. This chip-breaking feature is milled by a cutter 50 which has a plurality of teeth 52 (preferably a 20 or 32 tooth cutter is used). Each tooth 52 has a profile comprised of 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 point. Although only the "above centre" configuration has been shown in Fig. 11, it will be appreciated that the chip-breaking troughs could also be added to the "below centre" and "on centre" configurations depicted in Figs. 9 and 10.

As previously mentioned, the end view of the drill screw 10 (as shown in Figs. 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 generally convex point depicted in Figs. 1 to 8 and also shown in Fig. 1 4C consistently out-performs other point geometries when combined with the flute configuration previously discussed.

To form this generally conves 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 point form is shown in Fig. 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 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 + which is generally equal to the angle to be formed on the drill screw. Preferably both of these obtuse angles equal 172 < (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. Of course conventional single angle drill points such as 90 (Fig. 14A) and 105 (Fig. 1 4B) 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 generally convex point of Fig. 1 4C 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.

Claims

1. A self-drilling fastener having a shank and a drilling tip at one end of said shank, said tip including a pair of flutes lying on opposite sides of said fastener and extending at equal opposite angles with respect to the aixs of said fastener, a pair of heel portions extending intermediate said flutes, said heel portions intersecting to define a narrow chisel point, each of said flutes defining with said heel portions a cutting edge and a drag edge, and each of said flutes having a compound configuration, as viewed along the flute axis, formed by a straight section extending inwardly from the outer edge of said shank and including at least a portion of said cutting edge, and a curved section including at least said drag edge.

2. A self-drilling fastener according to claim 1 wherein, for each of said flutes, said curved section has a substantially uniform radius of curvature in a plane perpendicular to the flute axis.

3. A self-drilling fastener according to claim 1 or claim 2 wherein, for each of said flutes, said curved section includes a portion of said cutting edge.

4. A self-drilling fastener according to any one of claims 1 to 3 wherein said straight sections of said cutting edges, as viewed along the fastener axis, lie along a diameter of said fastener.

5. A self-drilling fastener according to anyone of claims 1 to 3 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 both of said flutes.

6. A self-drilling fastener according to anyone of claims 1 to 3 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.

7. A self-drilling fastener according to anyone of claims 1 to 6 wherein the included angle between said two heel portions at their intersection is 90 .

8. A self-drilling fastener according to anyone of claims 1 to 6 wherein the included angle between said two heel portions at their intersection is 1 OS'.

9. A self-drilling fastener according to anyone of claims 1 to 6 wherein each of said two heel portions comprises two generally planar surfaces.

1 0. A self-drilling fastener according to claim 9 wherein the pair of said planar surfaces adjacent said chisel point have an included angle of 105 while the pair of said planar surfaces adjacent said shank have an included angle of 90 .

11. A self-drilling fastener according to anyone of claims 1 to 6 wherein said two heel portions each has a convex configuration.

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

1 3. A self-drilling fastener according to claim 1 2 wherein each of said chip-breaking features comprises a shallow channel extending the length of, and generally parallel to the axis of, said flute.

14. A self-drilling fastener according to claim 1 and substantially as hereinbefore described with reference to Figs. 1 to 8, Fig. 9, Fig. 10, Figs. 11 to 13, or anyone of Figs.

1 4A to 14D, of the accompanying drawings.

1 5. A rotary milling cutter for fluting a drill screw shank, with each flute having at least one longitudinally-extending chip-breaking trough, said cutter comprising a cutter body, rotatable about a central axis, which has a plurality of cutting teeth positioned about the periphery thereof, the outer extremity of each of said teeth being formed as a semicircle with a rib formed thereon and each of said ribs having an arcuate configuration whereby, in use, the shank of the screw is shaped so that each of said flutes has a configuration, imparted by said rotating cutter body, which is generally complementary to at least a portion of one of said cutting teeth.

1 6. A method of fluting a drill screw shank, with each flute having at least one longitudinally-extending chip-breaking trough, said method comprising the use of a cutter including a cutter body, rotatable about a central axis, which has a plurality of cutting teeth positioned about the periphery thereof, the outer extremity of each of said teeth being formed as a semicircle with a rib formed thereon and each of said ribs having an arcuate configuration whereby, in use, the shank of the screw is shaped so that each of said flutes has a configuration, imparted by said rotating cutter body, which is generally complementary to at least a portion of one of said cutting teeth.

1 7. A rotary milling cutter for pointing a drill screw shank, with each pointing cut forming one-half of the drill point, said cutter comprising a cutter body rotatable about a central axis with a plurality of cutting teeth positioned about its periphery, the outer extremity of each of said teeth having a generally concave portion to engage and remove material from the drill screw shank, in use, to impart thereto one-half of a generally convex point.

18. A rotary milling cutter according to claim 1 7 wherein each of said generally concave portions is formed as a uniform radius.

1 9. A rotary milling cutter according to claim 1 7 wherein each of said generally concave portions is formed by two surfaces intersecting to form an obtuse included angle which is less than 180 .

20. A rotary milling cutter according to claim 1 9 wherein said obtuse included angle is substantially 172 > 1 72'.

21. A method of pointing a drill screw shank, with each pointing cut forming onehalf of the drill point, said method comprising the use of a cutter including a cutter body rotatable about a central axis with a plurality of cutting teeth positioned about its periphery, the outer extremity of each of said teeth having a generally concave portion to engage and remove material from the drill screw shank, in use, to impart thereto one-half of a generally convex point.