GB2100157A

GB2100157A - Pointing a drill screw shank to form a generally convex-sided point

Info

Publication number: GB2100157A
Application number: GB8223181A
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: 1982-12-22
Also published as: FI77094B; FI803666L; AT380733B; PT72081B; NZ195635A; CA1175688A; NO803548L; ES263215U; LU82954A1; IT8026206A0; DK151590C; IE51184B1; IE802443L; JPS6255006B2; DE3044001A1; AR224552A1; DK502480A; DK151590B; PT72081A; FR2470281B1

Abstract

A rotary milling cutter 58, for pointing a drill screw shank, has a plurality of peripherally positioned cutting teeth 60. The outer extremity of each of the teeth 60 is concave so that, in use, one-half of a generally convex point is imparted to the drill screw shank viz. heel portion 38 (heel portion 40 having been previously formed by a similar cutter). In an alternative arrangement, rotary milling cutter 66 has peripheral teeth 68 formed as two angular portions 70, 72. <IMAGE>

Description

1 GB2100157A 1

SPECIFICATION

Pointing a drill screw shank to form a generally convex-sided point The present invention relates to a rotary milling cutter for pointing a drill screw shank, and to a method of pointing a drill screw shank, so that each pointing cut imparts one-half of a generally convex-sided point.

In accordance with one aspect of the present invention, a rotary milling cutter for pointing a drill screw shank, with each pointing cut forming one-half of the drill point, corn- prises 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.

In accordance with another aspect of the present invention, a method of pointing a drill screw shank, with each pointing cut forming one-half of the drill point, comprises 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.

The generally convex point 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 172-11'. In this latter instance the drill point will have a compound included angle which may be 1OWC at the tip and WC elsewhere.

The present invention has been particularly developed for use in the manufacture of a self-drilling fastener forming the subject of our British patent application 8037945 (GB 2063731 A) which claims 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 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 said self-drilling fastener can drill with a lower end load, and in a shorter period of time even though the end load is reduced, in comparison with con- ventional self-drilling fasteners, and is 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 abovedefined configuration.

Those advantages 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, and in some arrangements said curved section includes a portion of said cutting edge.

Said self-drilling fastener is preferably man- ufactured using rotary milling cutters rather than the conventinal 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 said selfdrilling fastener, the fluting cutters are simul- taneously 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.

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

A rotary milling cutter, and a method, in accordance with 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 perpendi- cular to the chisel edge from line 4-4 of Fig.

Figure 5 is a side elevation taken parallel to a cutting edge from line 55 of Fig. 3; Figure 6 is a side elevation taken parallel to the chisel edge from line 6-6 of Fig. 3; GB2100157A 2 Figure 7 is a side elevation taken from line 77 of Fig. 3; Figure 8 is a sectional view taken along plane 8-8 of Fig. 7, a plane which is perpen5 dicular 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 alterna- tive 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 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 148 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, formed by application of the present invention, 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, formed by application of the present invention, 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 embody- ing 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 12 can be fully appreciated.

The self-tapping thread 14 may take any 105 convenient form.

The drill tip 12 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 to 1 W) 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 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 arrange ments of our co-pending British Patent Appli cation No. 8001756. Each flute then has a compound configuration which includes a straight portion 20, 22 and a curved portion 24, 26, here of uniform radius.]p the pre ferred 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 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 Fig. 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 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-men- tioned diameter, which is parallel to the two cuttting 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 Fig. 6. The intersection of the rotary milling cutters with the cylindric] 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.

Although Figs. 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 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 paraflel to a diameter of 3 GB2100157A 3 the drill screw, with said diameter intersecting 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 embodiment, 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 13 depict yet another arrange- ment of a drill screw to which the present invention can be applied. To date, chip-breaking features have only been added to forgedpoint drill screws. In the embodiment of the present invention shown in Figs. 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 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---abovecentre- configuration has been shown in Fig. 11, it will be appreciated that the chip-breaking troughs could also be added to the - below centreand---oncentre- configurations depicted in Figs. 9 and 10.

angular portions 70 and 72. These angular portions define an obtuse angle 4) which is generally equal to the angle to be formed on the drill screw. Preferably both of these ob- tuse angles equal 1 72-L' (as measured inter2 nally 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 9T, for example.

Conventional single angle drill points such as 90' (Fig. 1 4A) and 105' (Fig. 1413) fall outside the present invention but are illus- trated for purposes of comparison.

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. 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.

Protection for a rotary milling cutter for fluting a drill screw shank, and for a method of fluting a drill screw shank, so that each flute has at least one longitudinally-extending chip- breaking trough, is sought in our British patent application

Claims

1. A rotary milling cutter for pointing a drill screw shank, with each pointing cut form ing 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 extre mity of each of said teeth having a generally As previously mentioned, the end view of concave portion to engage and remove ma the drill screw 10 (as shown in Figs. 3,9,10) 105 terial from the drill screw shank, in use, to and the performance of the drill screw 10 will impart thereto one-half of a generally convex vary depending on the particular point added point.

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, prelimi nary testing indicates that the generally con vex 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 convex 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

2. A rotary milling cutter according to claim 1 wherein each of said generally con- cave portions is formed as a uniform radius.

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

4. A rotary milling cutter according to claim 3 wherein said obtuse included angle is substantially 1 72-yl'.

5. 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.

4 GB2100157A 4 Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Lid-1 982. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.