CA1217368A - Drill screw - Google Patents

Abstract

ABSTRACT

A drilling and thread forming fastener comprising a trailing threaded shank and a pilot end having a trans-verse major axis and a transverse minor axis. A pair of flutes extend longitudinally in the pilot end whereby to provide a pair of cutting surfaces. Each of the cutting surfaces is formed arcuately in the longitudinal direction to provide proper rake for drilling the flutes being oriented such that the cutting surfaces lie generally along the plane defined by the major axis of the pilot end and are coterminal with the major axis whereby cutting edges associated with the cutting surfaces describe a circle having a greater diameter than the minor axis when the fastener is rotated. Drag surfaces are formed by the flutes lying generally along the minor axis and coterminal there-with. Lands are provided intermediate the drag and cutting surfaces of increasing width in a radial direction from the drag surface to the cutting surfaces whereby the lands will not engage the sidewall of a pilot hole formed by the cutting surfaces. The improvement resides in that the drag surface is formed arcuately in the longitudinal direction of the fastener in substantially the same arcuate configuration as a said cutting surface to provide clearance for chips of material produced during the drilling process. The arcuate surface has substantially a constant radius throughout its length and extends from a point adjacent the tip of the pilot end to a point adjacent the threaded shank and is formed at an angle with respect to the cutting surfaces to provide a smooth flow of material through the flutes.

Description

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1 Background of the Invention The present invention is directed to a rotary threaded fastener or screw, and more particularly to a fastener of the type which drills a pilot hole, and forms threads in a workpiece, without the need for pre-drilling, tapping or the like.
In United States Patent 3,395,603 issued in the name of the present inventor and assigned to the assiynee of the present invention, there is provided a drilling and thread forming screw which has been manufactured in large 4uantities, and has met with great acceptance for use in the fields of automotive manufacturing, metal building construction, appliance fabrication, etc. The fastener generally comprises a pilot end which has a transverse major axis and a transverse minor axis, the length of the major axis being substantially as great as the minor axis. A pair of flutes are formed in the pilot end, each of which provides cutting surfaces essentially coterminal with the major axis and drag surfaces essentially coterminal with the minor axis.
While the invention of the above referenced patent has heretofore been employed in various size ranges of fasteners and for 12~3~8 1 various a~plications, there has risen a need for a fastener of the type described wherein the length of the pilot end is required to be substantially decreased such that the threaded portion of the fastener extends substantially closer to the tip than in the majority of applications in which the fastener is employed. However, it has been found that by shortening the tip length of the fastener, the drag surface as disclosed in the aforementioned U.S. Patent No. 3,395,603, when retained as a substantially flat surface, as discussed, is inclined at an angle which greatly inhibits thè flow of chips produced by the drilling operation from the opening being formed.
In view of the above, it is the object of the present invention to provide a drilling and thread forming fastener having a drill point of a configuration which aids in the removal of chips produced by the drilling operation and which may be employed over a broad range of drill tip sizes.

~2173~i8 The above object, and other objects are achieved in accordance with the broad aspect o~ the present invention by the provision of a drilling and thread forming fastener comprising a trailing threaded shank and a pilot end having a transverse major axis and a transverse minor axis. A
pair of flutes extend longitudinally in the pilot end whereby to provide a pair of cutting surfaces. Each of the cutting surfaces is formed arcuately in the longitudinal direction to provide proper rake for drilling the flutes being oriented such that the cutting surfaces lie generally along the plane defined by the major axis of the pilot end and are coterminal ~ith the major axis whereby cutting edges associated with the cutting surfaces describe a circle having a greater diameter than the minor axis when the fastener is rotated. Drag surfaces are formed by the flutes lying generally along the minor axis and coterminal there-with. Lands are provided intermediate the drag and cutting surfaces of increasing width in a radial direction from the drag surface to the cutting surfaces whereby the lands will not engage the sidewall of a pilot hole formed by the cutting surfaces. The improvement resides in that the drag surface is formed arcuately in the longitudinal direction of the fastener in substantially the same arcuate configuration as a said cutting surface to provide clearance for chips of material produced during the drilling process. The arcuate surface has substantially a constant radius throughout its length and extends from a point adjacent the tip of the 1~173~8 - 3a -pilot end to a point adjacent the threaded shank and is formed at an angle with respect to the cutting surfaces to provide a smooth flow of material through the fl~utes.

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~73~8 1 Description of the Drawing For a more complete understanding of the invention reference should be made to the accompanying drawing taken in conjunction with the following description of a preferred embodiment, wherein:
Figure 1 is an elevational view of a drilling and thread forming fastener constructed in accordance with the prior art;
Figure 2 is a side elevational view of the prior art fastener of Figure 1 taken at 90 to Figure 1, Figure 3 is an end view of the prior art fastener of Figures 1 and 2;
Figure 4 is an end perspective view of a drilling and thread forming fastener constructed in accordance with the teachings of the present invention;
Figure 5 is a side elevational view showing the fastener of Figure 4;
~ Figure 6 is an elevational view of the fastener of Figures 4 and : 5 taken at 90 to the view shown in Figure 5; and Fiyure 7 is an end view of the fastener shown in Figures 4 ; through 6, showing further details of the invention.

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l Description of the Preferred Embodiment Referring now to Figures 1, 2 and 3 which are labelled prior art, there is shown a prior art fastener, of the drilling and threaded forming type, substantially as described in the aforementioned U.S.
Patent No. 3,395,603.
The fastener generally comprises a screw body 10 having an elongated shank 12 with a head 14 integral with a trailing end thereof. The screw body 10 further is provided with a pilot end 16 of substantially elliptical transverse configuration. As in the prior art structure referred to, the term elliptical is here used for purposes of description of visualization only and is not intended in a strict mathematical sense. Longitudinally extending flutes or slots 18 and 1~ of similar construction are formed in opposite quadrants of the pilot end 16. The flute 18 is defined by a cutting surface 20 having cutting edges 22, 24 and by a drag surface 26. The flute 19 is defined by a cutting surface 28 having cutting edges 30 and 32, and by a drag surface 34. The cutting surfaces 20 and 28 are slightly arcuate and lie generally in a plane which has a small amount of angularity with respect to the longitudinal axis of the screw to facilitate removal of material from the cutting edges during the cutting operation. The contour of the surfaces 20 and 28 as shown in Figure 3 provides the proper cutting angle and rake at the cutting edges 22 and 24. The drag surfaces 26 and 34 are angularly disposed with respect to the longitudinal axis of the screw to facilitate discharge of material removed in the cutting operation.

~2173~l3 l In figure 3, the maximum width of the cutting surfaces 20 or 28 is shown to be greater than the maximum width of the drag surfaces 26 or 34. The cutting surfaces 2G and 28 lie generally offset from and parallel to the transverse major axis a of the elliptical pilot end to define the major axis. The drag surfaces 26 and 34 lie in a similar relation to the transverse axis b. A pilot hole cut by the cutting edges 22, 24 and 30, 32 therefore will be of greater diameter than the minor axis b of the pilot end. Thus, the drag surfaces 26 and 34 which define the minor axis b will not engage the sidewalls of a pilot hole cut by the cutting edges. Likewise, the arcuate portions of the pilot end intermediate the cutting and drag surfaces, designated as lands 36 and 38 will also not engage the sidewalls of a pilot hole.
The description of Figures 1 through 3 thus far, has been that of the structure shown in the U.5. Patent No. 3,395,603, and further 15 discussion as to the advantages and details of the structure can be found by referring to that patent.
Referring now to Figures 4 through 7, there is shown a fastener similar to that described heretofore, but with the incorporation of the teachings of the present invention.
In Figures ~ through 7 there is shown a fastener having a screw body 110 comprising a shank section 112 and a pilot end 116. The fastener is further provided with longitudinally extending flutes 118 and 119 formed in opposite quadrants of the pilot end 116. The flute 118 is partially defined by a cuttins surface 120 having cutting edges 25 122 and 124. In like manner, flute 119 is partially defined by ~7~ ~L~73~8 1 cutting surface 128 having cutting edges 130 and 132. The arcuate portions of the pilot en~ 116 which are defined by the cutting surfaces 120 and 128 are herein referred to as lands 146 and 148.
The fastener thus far described is similar in construction to the prior art fastener set forth above, and shown in Figures 1 through 3, like portions being given like reference numerals with the addition of the prefix 1.
Referring now to Figure 6, the length of the pilot end L is shown to be measured from the tip of the pilot end to the last thread designated T. As heretofore referred to, in many applications of the fastener it is desirable to have the length L decreased in order to provide greater penetration of the threads provided on the fastener shank, while still retaining the standard length of fastener. In this instance, the angle that the drag surface 26 or 34 of the prior art fastener assumes with respect to the surface to which the fastener is applied becomes smaller, providing less area in which drilling chips may be removed through the flute 18 or 19 in the prior art fastener.
This situation leads to a clogging of the flute with drilled material, and may slow the drilling time of the fastener, producing a less desirable fastening operation.
In the improved fastener shown in Figures 4 through 7, the problem has been alleviated by providing drag surfaces 40 and 42 constructed in a manner to produce a greater volume of space through which drilling material may pass, and to provide a surface which guides the drilling material upwardly and away from the pilot end 116 12173~8 1 Of the screw body 110.
As will be noted in Figure 7, the drag surfaces 40 or 42 are formed on a plane which is disposed at an angle with the plane of the center line of the fastener body 110 and at 90 with the plane of the cutting surface 120 or 128, respèctively. That is, the plane of the drag surfaces 40 or 42 is disposed at an angle of 90 plus from the cutting surface 120 or 128. In practice the angle is generally in the area of 15~, and the angle of the drag sur-Face 40 or 42 with the cutting surface 120 or 128 is 105 . This angle has been employed in prior constructions but has not in itself relieved the problems set forth above, when the drag surface 40 or 42 is disposed at an extreme acute angle with the work surface to be drilled by the fastener.
In the present embodiment, a radius R is formed in a continuous manner, and is constant from the tip of the fastener to a point substantially adjacent the last thread T of the fastener. The radius R, which may be of a length sufficient to achie~e the necessary clearance required ~or chip remo~al, is formed at right angles to an imaginary plane 105 from that of the cutting surface 12Q or 12~ along 20 a line substantially following that of the centerline shown in Figure 6. That is, the imaginary plane referred to would be the plane of the drag surface, according to the prior art. In practice, it has been found that a radius R which is substantially equal to that employed in the surfaces 120 and 12~ to pro~ e the proper C~llttill(`, 25 angle at the cutting edges, pro~ides the satist`actory relief to allo ~2173~t3 1 smonth flow of material through the flutes 118 and ll9.
In effect, the continuous arcuate surface in the longitudinal direction cf the fastener provides a clearance for chips to be removed during the drilling operation and also a surface which is conducive to mo~;ng the chips in a cont;nuous manner from the opening being dr;lled by the fastener 110. Thus, the objective of the invention is ach;eved by the sirnple expedient of forming a continuous arcuate surface on the drag surface 40 and 42 of the fastener similar to that of cutting surfaces 120 and 128 of the fastener, which serves the purpose of providing the increased area required to remove chips during the drill;ng operation~ and a surface which is in all respects conducive to mo~ing the chips formed by the drilling fastener upwardly and out of the opening.

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a drilling and thread forming fastener comprising a trailing threaded shank and a pilot end, said pilot end having a transverse major axis and a transverse minor axis, a pair of flutes extending longi-tudinally in the pilot end whereby to provide a pair of cutting surfaces, each of said cutting surfaces being formed arcuately in the longitudinal direction to provide proper rake for drilling said flutes being oriented such that said cutting surfaces lie generally along the plane defined by the major axis of said pilot end and are coterminal with said major axis whereby cutting edges associated with said cutting surfaces describe a circle having a greater diameter than said minor axis when said fastener is rotated, drag surfaces formed by said flutes lying generally along said minor axis and coterminal therewith, and lands intermediate said drag and cutting surfaces of increasing width in a radial direction from said drag surface to said cutting surfaces whereby said lands will not engage the sidewall of a pilot hole formed by said cutting surfaces, the improvement comprising said drag surface being formed arcuately in the longitudinal direction of said fastener in substantially the same arcuate configuration as a said cutting surface to provide clearance for chips of material produced during the drilling process, said arcuate surface having substantially a constant radius throughout its length and extending from a point adjacent the tip of the pilot end to a point adjacent the threaded shank and being formed at an angle with respect to said cutting surfaces to provide a smooth flow of material through said flutes.

2. A drilling and thread forming fastener as set forth in claim 1 wherein said arcuate surface radius is formed at right angles to an imaginary plane greater than 100° from that of said cutting surface.