CA1042243A

CA1042243A - Drill screw

Info

Publication number: CA1042243A
Application number: CA248,546A
Authority: CA
Inventors: Brian Brindle
Original assignee: WA Deutsher Pty Ltd
Current assignee: WA Deutsher Pty Ltd
Priority date: 1975-04-02
Filing date: 1976-03-23
Publication date: 1978-11-14
Also published as: SE7603878L; DE2613720C2; FR2306362B3; JPS541852B2; JPS51123461A; IT1058887B; GB1513085A; DE2613720A1; AU1224676A; ES446572A1; FR2306362A1; SE441382B

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to drill screws with extending ears to ream a hole in object with the ears breaking off when the screw enters a second object in which a smaller hole is drilled. The inventive screw is adapted to fasten two or more juxtaposed work pieces and it comprises a tip, a shank, and a head, a screw thread on a substantial part of the length of the shank, and means projecting from a part of the shank lying between the tip and the thread.
The projecting means is integral with the shank and operative in materials of less than a predetermined hardness to form a hole having a diameter at least as great as the pitch diameter of the thread, but being so weakly connected to the shank that, in materials of more than the predetermined hardness, the projecting means is broken. The projecting means is of non-rectangular configuration and is such that upon being broken there is substantially none of the pro-jecting means remaining which projects beyond the shank.

Description

o~ 3 This invention relates to impro~ements in and relating to drill screws of the type described generally in Canadian Patent No. 809,403, Issued April 1, 1969, - that is to say, to screws having laterally extending ears or wings for enlarging a hole formed by the screw in one object and which are made to break off when the screw has entered a second object. The invention refers particularly to the manufacture of such screws.
, The tools used in the manufacture of such screws, for the formation of the lateral ears or wings (hereinafter referred to as wings), are generally rectangular in profile and have a limited life due to chipping of the corners of the tools caused by the high streses associated with those sharp corners. Also, the rectangular tools can cause build-up of the wing adjacent the screw shank, such build-up acting as a strengthening rib in the edge of the wing and ` requiring increased force to break off the wing. Further, this build-up causes the wings to countersink the material being drilled and tapped, thus reducing the strength of the fastening by reducing the number of threads tapped.
Additionally, the wings tend to fracture at a location outside the shank of the screw and the resultant rough '~
edge tends to ream the drilled hole and so reduce the depth of thread formed by the screw, reducing the strength , of the fastening.
; It is the principal object of this invention to ` provide improvements in the manufacture of these winged .:.~ .:
drill screws devised for the purpose of eliminating the -disadvantages set out above.
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4ZZ~3 The object is a~tained by the inyention which contemplates a screw adapted to fasten two or more juxtaposed work pieces comprising a tip, a shank, and a head, a screw thread on a substantial part of the length of the shank, and means projecting from a part of the shank lying between the tip and the thread.
The projecting means is integral with the shank and operative in materials of less than a predetermined hardness to form a hole having a diameter at least as great as the pitch diameter of the thread, but being so weakly connected to the shank that, in materials of more than the predetermined hardness, the projecting means is broken. The projecting means is of non-rectangular configuration and is such that upon being broken there is sub-stantially none of the projecting means remaining which projectsbeyond the shank.
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In a further embodiment, the invention contemplates a drilling and reaming screw adapted to fasten two or more juxta- -posed workpieces and which comprises a drill tip, a shank, and j, a head, a screw thread on a portion of the length of the shank, ~, and two or more frangible, reaming means projecting from a region ~ 20 of the shank intermediate the tip and the thread and pinched from -' the shank material. The projecting means is integral with the ~
`~ shank and is operative in materials of less than a predetermined `
hardness to form a hole having a diameter at least as great as ` the pitch diameter of the thread, but being so weakly connected !~
to the shank that the projecting means is thereby adapted to be ` broken and separated from the shank in materials of more than the . ,., :
predetermined hardness. The projecting means includes an outer portion extending radially beyond the shank surface to a radius at least as great as the crest radius of the thread, and an inner portion extending radially inwardly from the shank surface to a juncture line. That juncture line includes upper and lower segments with each segment intersecting the shank surface at an acute angle to the shank surface so that no harmful projecting buildup occurs at the juncture of the projecting means with the

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~)4~3 outer surface of khe shank.

In an additional embodiment, the invention contemplates a , .
drill screw adapted to fasten together two or more juxtaposed workpieces, which comprises a drill tip, a shank, and a head.
A screw thread is provided on a portion of the leng-th of the shank, and two or more frangible means projecting from a region of the ~ shank intermediate the tip and the thread and pinched from the ,',`!, shank material. The projecting means is operative in materials ., of less than a predeter~lned hardness to form a hole having a diameter at least as great as the crest diameter of the thread, but being so weakly connected to the shank that the projecting means is thereby adapted to be broken and separated from the shank upon a predetermined resistance to turning. The projecting means extends radially beyond the adjacent outer shank surface to ,.. .. .
a radius at least as great as the crest radius of the thread and , extends radially inwardly from the adjacent outer shank surface to a juncture line. That juncture line intersects the adjacent outer .. ..
shank surface at an obtuse angle to the shank surface, so that no ~ harmful projecting build-up occurs at the juncture of the project-i~ 20 ing means with the adjacent outer surface of the shank.
, According to this invention the punch tools for the product- -~
ion of the wings in winged drill screws of the type described .~o ;
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~' not have sharp corners at their extremities. Thus, as compared to screws described in Canadian Patent No. 809,403, there is less ~,. .. .
;~ tendency to build-up at the locations where the wings join the shanks. The punch tools may be circular in section, to provide ~.,~; . . . .
i~ an arcuate indentation in the screw shank, or elliptical in cross-section, or of irregular hexagonal shape with a short inner edge, an outer edge parallel thereto, front and rear ends at right angles ~;~ 30 to the outer edge and inclined edges joining the inner extremities ; of the front and rear ends and the short inner edge; or similar to :
;;; the latter but with arcuate edges joining the front and rear ends to the short inner edge, or of other satisfactory shape.
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~ ' , - ~L04Z~:43 In order that the in~ention may be clearly understood and readily put into practical effect there shall now be described some preferred forms of drill screws according to the present invention, the description being by way of example only and with reference to the accompanying illustrative drawings. In the drawings:-Figure 1 is an elevation of the screw of the aforementionedpatent;
Figure 2 is a schematic elevational view showing the screw of Figure 1 with one tool still in place;
Figure 3 is a schematic elevational view corresponding to Figure 2 showing the screw after the wings have been fractured;
;i Figure ~ is a schematic perspective view of the screw of Figures 1 and 2 showing a wing prior to fracture;
Figure 5 is the screw of Figure 4 after fracture of the wing;
Figure 6 is a schematic elevational view of a screw of the -present invention with one tool still in place;
Figure 7 is a schematic elevational view corresponding to , Figure 6 showing the screw after the wings have been fractured;
Figure 8 is a schematic perspective view of the screw of ~ ~;
Figure 6 showing one wing prior to fracture;
,~ Figure 9 is the screw of Figure 8 after the fracture of the wing;
Figure 10 is a schematic elevational view of a second screw of the present invention with one tool still in place;
Figure 11 is an elevation of a third screw of the present invention; and ' Figure 12 is a schematic elevation showing the screw of Figures 10 and 11 after use.
Referring now to Figures 1 to 5, the prior art screw 10 shown has a shank 12 having threads 14 along a substantial portion of its extent, a tip 16 at its entering end and a head 18 provided with suitable driving means (not shown) at the opposite end. The tip 16 in the embodiment disclosed - 4 ~

is provided with ~rilling flutes of the type disclosed in U.S. Patent No. 3,125,923, but for purposes of the present inven-tion drill points of other configurations can be used with equal facility. Similarly, the threaded portion 14 of shank 12 may have a slot providing a cutting edge in the entering portions of the threaded section 14 for purposes of cutting threads in a workpiece.
Intermediate the tip 16 and the threaded portion 14 of the shank 12 there is provided a pair of ears 22 which are struck from the parent material of shank 12 by any suitable means such , as pinch pointing, which is well known in the art. This is generally accomplished by exerting pressure by dies 26 transverse ; to the axis of the screw and forcing material from the shank to `~
be extruded laterally resulting in slots 24 (Figure 4) where material has been removed to form the laterally extending ear 22. Each ear ~ -22 extends outwardly from the shank 12 a radial distance equal to or greater than the major diameter of the threaded portion 14. In . "
some instances, however, this radial dimension can be limited to a point where it is less than the major diameter but greater than the pitch diameter of the tllreads on said shank. Ears 22 are so dimensioned as to control their physical strength.
The purpose of the screw is to fasten together two super-imposed panels (such as the panels 40 and 42 shown in Figure 12), the first panel being softer than the second. The screw tip 16 drills a hole through the panels, and the ears 22 counterbore the hole in the first panel, so that the threaded portion 14 is a :. .' .
clearance fit in the first panel. When the ears 22 reach the second panel they become broken from the shank as a consequence of the greater hardness of the second panel. The threaded portion 14 then taps a cooperating thread in the bore through the second panel.
As a result of the forcing of the material from shank 12 by die 26 to form ear 22, it has been found in practice that a build-up of material 28 occurs at each longitudinal end of the . ~, ...
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~)4ZZ~3 ear 22 at the junction thereo~ with shank 12, This means that when the ears 22 are broken off ~n use, snags 30 remain where the build-ups 28 were before fracture. These snags 30 project radially beyond the outer surface of shank 12 and hence act as counter~boring tools. This naturally, decreases the effectiveness of the operation of the screw 10 as the remaining material in a panel into which the threaded portion 14 i9 to engage is signifi-cantly less than the depth of the threads and hence the security of the fastening is diminished. The curved shape of the fracture line 32 (Figure 3) is due to the inherent strength of the material.
To refer now to Figures 6 to 9, there is shown a screw according to the present invention. Like parts are given like reference numerals with the addition of the prefix number 1. Here, the shank 112 has two diametrally opposed arcuate slots 124 and ears 122 of approximate circular shape and which are formed by circular dies 126. As can be seen, it has been found that with the arcuate juncture line between each ear 122 and the shank 112, there is no or very little build-up at the junctions 125 of the ears 122 with the outer surface of shank 112 and that, in consequence, the fracture line 132 does not extend beyond the outèr surface of shank 112 to form snags. In this way the performance of the screw is greatly improved as compared with screws as shown in Figures 1 to 5. Furthermore, as they have no sharp corners, the dies 126 have a far greater life expectancy than the dies 26.
Referring now to Figure 10, there is shown a second screw i~ ~
according to the present invention and where, again, like parts ~ -are given like reference numerals with the addition of the prefix `~
~, .. ~ ,, ' number 2. The screw shown here is used to provide a countersink -.; , ..... .
for the head of the screw rather than a counterbore to allow free `l 30 passage for the threaded portion.

Here, the shank 212 has two diametrally opposed ears 222 formed by dies 226. The dies each have a side 240 substantially ~!.` -- 6 r~ :

~L~422~3 ~` parallel to the axis of the shank 212, a forwardly and outwardly extendlng side 242 at a re~atively shallow angle to the axis of the shank 212 - less than 45 and preferably about 30 - and a rearwardly and outwardly extending side 244 at a greater angle to the axis of the shank ~ as at about 45, or between 30 and 60.
; The ears 222 extending from the shank 212 have rear edges 246 ~ -: " .
(i.e. edges furthest from the tip 216) substantially normal to , ; the line of the shank 212, front edges extending at a shallow angle to the line of the shank 212 ~ as, for example, at about 30 or even less - and an outer side 250 curved for the major part.
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This form of ear 222 will firstly form a countersink so as to accommodate the head of the screw, and thereafter the ears will become broken away. ;
The screw of Figure 11 is the same as that of Figure 10 except that a radially inwardly and axially upwardly directed notch 234 is provided in the front edge 248' of each ear 222'.
In this way each ear 222' is divided into a front portion 236 which countersinks and recesses the hole and a second portion 238 o enlarged radial dimensions which contacts the material surrounding the countersunlc and recesses hole to produce a pre-determined resistance to turning and so cause both ears 222' to be broken away.
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The operation of the embodiment of Figure 11 is shown in Figure 12 where the screw is used to fasten two superposed -i i panels 40 and 42 of dissimilar materials. The first panel or -work member 40 is softer than the second work member or panel 42.
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When the screw is applied by axial pressure from the head and ;~ -. ~ j,..... .
` rotated, the tip 216 will create its own bore through panel 40.
As the screw advances, the portions 236 of the ears 222' act as countersinkers to enlarge the diameter of the bore to form a countersunk recess 44. When the countersunk recess 44 has been formed, second portion 238 will contact upper surface of panel ~-.~ , . ~` . .

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- 40 at 46, Consequently the ears 222' experience an increased resistance to turning, such that the ears become broken and ~:. separated from the shank of the screw.
It is believed that the screws provided by this invention :
will be a marked improvement over the known winged drill screws . and will gain an ever greater acceptance in industry and commerce.
Modification in details of construction and design may be made without departing from the ambit of the invention, the nature , ,. of which is to be ascertained from the following claims. ~:

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Claims

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

1 A drill screw adapted to fasten together two or more juxtaposed workpieces, comprising a drill tip, a shank, and a head, a screw thread on a portion of the length of the shank, and two or more frangible means projecting from a region of the shank intermediate the tip and the thread and pinched from the shank material, the projecting means being operative in materials of less than a predetermined hardness to form a hole having a diameter at least as great as the crest diameter of the thread, but being so weakly connected to the shank that the projecting means is thereby adapted to be broken and separated from the shank upon a predetermined resistance to turning, characterized in that the projecting means extends radially beyond the adjacent outer shank surface to a radius at least as great as the crest radius of the thread and extends radially inwardly from the said adjacent outer shank surface to a juncture line, the juncture line intersecting the said adjacent outer shank surface at an obtuse angle therewith, so that no harmful projecting build-up occurs at the juncture of the projecting means with the said adjacent outer surface of the shank.

2. A drill screw as claimed in Claim 1, wherein the outer portions of the projecting means have a rear edge ex-tending substantially normal. to the axis of the shank, a front edge extending at an acute angle to the axis of the shank, and a radially outer side curved for the major part.

3. A drill screw as claimed in Claim 2, wherein said front edge is provided with a radially inwardly and axially rearwardly directed notch.

4. A drill screw as claimed in Claim 1, Claim 2 or Claim 3, wherein the projecting means are substantially of circular configuration.