IE51185B1 - Fluting a drill screw shank to form a chip-breaking trough - Google Patents

Description

The present invention relates to a rotary milling cutter for fluting a drill screw shank, and to a method of fluting a drill screw shank, so that each flute has at least one longitudinally-extending chip-breaking trough.

In accordance with one aspect of the present invention, a rotary milling cutter for fluting a drill screw shank, with each flute having at least one longitudinally-extending chipbreaking trough, comprises a cutter body, rotatable about a central axis, which has a plurality of cutting teeth positioned about the periphery thereof, a cutting edge at 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 one of said cutting teeth „ In accordance with another aspect of the present invention, a method of fluting a drill screw shank, with each flute having at least one longitudinally-extending chip-breaking trough, comprises the use of a cutter including a cutter body, rotatable about a central axis, which has a plurality of cutting - 2 5118 5 teeth positioned about the periphery thereof, a cutting edge at 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 one of said cutting teeth.

The provision of the ribs on the teeth leads to the formation of a shallow channel in each flute constituting the longitudinally-extending chip-breaking trough.

The present invention has been particularly developed for use in the manufacture of a self-drilling fastener forming the subject of our patent application No. 2443/80.

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 conventional self-drilling fasteners, and is further capable of drilling satisfactorily high-strength, low-alloy steels, which has hitherto not been possible.

Said self-drilling fastener may include, as one of the steps in its manufacture, a preferred embodiment of the method of fluting in accordance with the present invention, involving simultaneously plunging a pair of the rotary milling cutters in accordance with the present invention into the shank of a screw blank along axes of movement which are parallel, but offset. - 3 18S 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 to produce a generally convex-sided drill point.

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, selftapping screw claimed in our patent application No. 2443/80 to which the present invention can be applied; 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 perpendicular 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; - 4 51185 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 screw in which the cutting edges are below centre; Figure 10 is an end view of another alternative screw in which the cutting edges are on centre; Figure 11 is an end view of a drill screw formed by application of the present invention to present 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 148 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 for 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 - 5 of a cutter for forming this point.

Before particularly describing the present invention, it will be convenient to discuss a self-drilling, self-tapping fastener 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 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 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 Figure 8) respectively to each of the flutes. The feed may be somewhat similar to the feed arrangements of our patent Application No. Sooflfjj. Each flute then has a compound configuration which includes a straight portion 20, 22 and a curved portion 24, 26, here of uniform radius. Preferably these straight portions 20, 22 include cutting edges 28 and 30 while the radiused portions 24 and 26 - 6 51185 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 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 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 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, 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 - 7 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.

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 a 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 - 8 51185 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 arrangements, 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.

The present invention can be applied to the selfdrilling, self-tapping screw 10.

To date, chip-breaking features have only been added to forged-point 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 or 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. - 9 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 convex-sided point depicted in Figures i 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 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 arrangement 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 arrangement 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 d which is generally equal to the angle to be formed on the drill screw.

Preferably both of these obtuse angles equal 172i° (as measured internally qnthe 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° (Figure 14A) and 105° (Figure 14B) - 10 51185 could be used 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.

Protection for a method of pointing a drill screw shank so that each pointing cut imparts one-half of a generally convex-sided point is sought in our patent application no. 51186

Claims (4)

1. 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, 5 rotatable about a central axis, which has a plurality of cutting teeth positioned about the periphery thereof, a cutting edge at 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 10 shaped so that each of said flutes has a configuration, imparted by said rotating cutter body, which is generally complementary to one of said cutting teeth.

2. A method of fluting a drill screw shank, with each flute having at least one longitudinally-extending chip-breaking trough, 15 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, a cutting edge at 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 20 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 one of said cutting teeth

3. A method of fluting a drill screw shank substantially as 25 described herein with reference to the accompanying drawings. - 12 51185

4. A drill screw shank which has been fluted by a method as claimed in Claim 2 or Claim 3.