Note: Descriptions are shown in the official language in which they were submitted.
~75~
BACKGROUND ~ND SUMMARY OF THE INVENTION
The present invention relates to a novel drill screw
which is capable of improved performance and to cutters for
making it.
Many different 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 for some applications, 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-pressure 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 loading required
and drill time will be of benefit to both the individual
workman and to his employer.
2S Therefore, the present invention seeks to provide a
drill screw capable of drilling with lower end-pressure load.
Further the invention seeks to provide a drill screw
that can drill in a shorter period of time even though the
end load is reduced.
3~ Further, the present invention seeks to provide a drill
screw which is capable of drilling high-strength, low-alloy
steels.
In one aspect the invention comprehends a self-drilling
fastener having a fastener shank with an axis and an outer
edge and further having a drilliny tip at one end of the
fastener shank, the tip comprising a pair of flutes extending
at equal opposite angles with respect to the axis of the
fastener lying generally on opposite sides thereof. A pair
of heel portions extend intermediate the flutes, the pair
of heel portions intersecting to define a narrow chisel point.
Each of the pair of flutes defines a cutting edge and a drag
surface with portions of the tip between the pair of flutes
and axially inwardly of the heel portions being configured
in substantially immediately increasing cross-sections in
planes through the heel portions parallel to the axis of the
fastener as distance along the planes from the heel portions
increases thereby buttressing the cutting edges and enhancing
resistance of the tip to breaking during drilling. Each of
the pair of flutes adjacent the heel portions has a compound
configuration formed by a straight section extending inwardly
from the outer edge of the shank and including at least a
portion of one of the cutting edges and a curved section
including at least one of the drag surfaces, the curved section
having a substantially uniform radius of curvature in a plane
perpendicular to the axis of one of the pair of flutes.
The invention also comprehends a sel~-drilling fastener
having a drilling tip at one end of a substantially cylindrical
fastener shank having an outer edge and a longitudinal axis,
the tip comprising a pair of flutes extending at equal opposite
angles with respect to the longitudinal axis of the shank
and lying generally on opposite sides thereof. A pair of
heel portions each presenting a heel surface extend
intermediate the pair of flutes, the heel surfaces intersecting
to define a narrow chisel point. Each of the pair of flutes
defines a drag surface and intersects with the heel surfaces
to form a cutting edge and a drag edge, and each of the pair
of flutes adjacent the heel portions has a compound
configuration formed by a straight section extending inwardly
from the out,er edge of the shank and including at ]east a
~ 2 -
~5~
\
portion of one of the cutting edges and a curved section
including at least one of the drag surEaces. The curved
section has a substantially uniform radius of curvature in
a plane perpendicular to the axis of a respective one of the
pair of flutes, the included angle of each of the cutting
edges defined by the respective one of the pair of flutes
and the heel surface varying over the length of each of the
cutting edges with the most acute value of that angle
occurring at the outer edge of the shank, thereby presenting
a sharply relieved cutting edge to a workpiece.
The invention in a further aspect comprehends a self-
drilling fastener having a drilling tip at one end of a
substantially cylindrical fastener shank having a longitudina]
axis and an outer surface, the tip comprising a pair of flutes
extending at generally equal opposite angles with respect
to the longitudinal axis of the shank and lying generally
on opposite sides thereof. A pair of heel portions each
presenting a heel surface extend intermediate the pair of
flutes, the heel surfaces intersecting to define a narrow
chisel point. Each of the heel surfaces further intersects
a portion of the outer surface of the shank to form an arcuate
edge andeach of the heel surfaces lies entirely on one side
of a plane containing the chisel point and a respective one
of the arcuate edges. Each of the pair of flutes defines
a drag surface and intersects with the heel surfaces to form
a cutting edge and a drag edge. Each of the heel portions
is configured in substantially immediately increasing cross-
section in planes parallel to the axis of the fastener as
distance along the planes from the drilling tip increases
thereby buttressing each of the cutting edges and enhancing
resistance of the tip to breaking during drilling. Each of
the pair of flutes adjacent the heel portions has a compound
configuration formed by a straight section extending inwardly
from the outer surface of the shank and includes at least
a portion of each of the cutting edges and a curved section
- 3 -
including at least each of the drag surfaces. The curved
section has a substantially uniform radius of curvature in
a plane perpendlcular to the axis of a respective one of the
pair of flutes.
A still further aspect of the invention comprehends
a self-drilling fastener having a drilling tip at one end
of a substantially cylindrical fastener shank having a
longitudinal axis and an outer surface, the tip comprising
a pair of flutes extending at generally equal opposite angles
with respect to the longitudinal axis of the shank and lying
generally on opposite sides thereof. A pair of heel portions
each presenting a heel surface extend intermediate the pair
of flutes with the heel surfaces intersecting to define a
portion of the outer surface of the shank to form an arcuate
edge and each of the heel surfaces lies entirely on one side
of a plane containing the chisel point and respective one
of the arcuate edges. Each of the pair of 1utes defines
a drag surface and intersects with the heel surfaces to form
a cutting edge and a drag edge. Each of the heel portions
is configured in substantially immediately increasing cross-
section in planes parallel to the axis of the fastener as
distance along the planes from the drilling tip increases
thereby buttressing each of the cutting edges and enhancing
resistance of the tip to breaking during drilling. Each of
the pair of flutes adjacent the heel portions has a compound
configuration formed by a straight section extending inwardly
from the outer surface of the shank and includes at least
a portion of each of the cutting edges and a curved section
including at least each of the drag surfaces. The curved
section has a substantially uniform radius of curvature in
a plane perpendicular to the axis of a respective one of the
pair of flutes, the included angle of each oE the cutting
edges defined by the respective one of the pair of flutes
and the heel surface varying over the length of each of the
cutting edges with the most acute value of that angle occurring
,j~ - 4 -
at the outer surface of the shank, thereby presenting a sharply
relieved cutting edge to a workpiece.
As disclosed, the invention pertains to a drill screw
which has a compound flute configuration; that is, a flute
which has both a straight section and a curved section, the
radius of this curved section being uniform in a plane
perpendicular to the axis of the flute. The straight section
includes at least a portion of the cutting edge and the curved
section includes at least the trailing or drag surface. In
some embodiments, the curved section also includes part of
the cutting edge (defined as that portion of the leading end
of the flute which is in advance of the chisel).
The drill screw of the present invention is manufactured
using radiused cutters rather than the conventional fluting
and pointing saws. One of the chief benefits of using radiused
cutters is that, unlike conventional saws, when the teeth
are sharpened, little or no material is removed from the
diameter~ Hence, the optimum 1ute 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 configurati.on which is less subject to deflection.
In the manufacture of these drill screws, the fluting
cutters are simultaneously plunged into the shank of the screw
blank along axes which are parallel, but offset. The
longitudinal a~es of the cutters are inclined at equal but
opposite acute angles relative to the axis of the blank as
the cutters are moved along the parallel axes of movement.
As a result, the flute has a straight section corresponding
to the side of the cutter and a radius corresponding to the
tip radius of the cutter teeth.
The drill screw may be provided with any of the
conventional 90O or 105 point angles or, may be formed by
a cutter which has a generally concave tooth configuration.
This will produce a generally convex point, each portion of
- 5 -
6~3~
which may have a uniform radius of curvature or be formed
by a pair of planar surfaces which intersect to form an
included angle of 172~- In this latter instance the dri~l
point will have a compound included angle which may be 105
at the tip and 90 elsewhere.
The drill screw of the present inventlon has a stronger
cutting edge which makes it less likely to break down when
drilling the harder materials. At the same time, by
maintaining a comparatively narrow chisel, the end pressure
required to effect drilling can be kept to a minimum.
These and other aspects, features and advantages of
the present invention will be better understood by referring
to the following detailed description taken in conjunction
with the accompanying drawings.
~3RIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation of a self~drilling, self-
tapping screw embodying the present invention;
FIG. 2 is an end view of the drill screw of one
embodiment of the present .invention taken along line 2 - 2
of Fig. l;
FIG. 3 is an enlargement of the drill point shown in
Fig. 2;
FIG. 4 is a side elevation of the drill point taken
perpendicular to the chisel or along line 4 - 4 in Fig. 3
FIG. 5 is a side elevation taken parallel to the cutting
edge or along line 5 - 5 of Fig. 3;
FIG. 6 is a side elevation taken along line 6 - 6 of
Fig. 3, a line parallel to the chisel;
FIG. 7 is a side elevation taken along line 7 - 7 of
Fig. 3;
FIG. 8 is a sectional view taken along line 8 - 8 of
Fig~ 7, a line which is perpendicular to the axis of one of
the flutes;
FIG. 9 shows an end view of a slightly varied form of
the present inven-tion in which the cutting edges are beyond
- 6 -
center (i.e., both extend beyond the same diametral plane);
FIG. 10 is another alternate embodiment in which the
cutting edges are generally coaxial (i.e., on center);
FIG. 11 shows an end view of an embodiment of the present
invention which has a chip-breaking featuxe;
FIG. 12 is a side elevational view of the Fig. 11
embodiment taken along line 12 - 12;
FIG. 13 is a sectional view taken along line 13 - 13
of FigO 12 and showing the fluting cutter with which it is
made;
FIG. 14A is a non-fluted blank with a 90 point angle;
FIG. 14B is a side elevational view of a standard 105
point angle;
FIG. 14C is a side elevational view of one form of the
generally convex point showing the configuration of the cutter
for forming same; and
FIG. 14D is a side elevational view of an alternate
form of the generally convex point each heel thereof formed
by a pair of angulated surfaces and showing the tooth
configuration of the cutter Eor forming this point.
.
- 7 -
Case ~o. 3526-00
I~E TAILED DESCRIPTIO~ OF THE INVENTION
The self-drilling, self-tapping fastener of the present invention
is shown generally at l0. Figures 1-8 show a plurality of views of
the pre~erred embodiment in order that the precise configuration of
the drill tip 12 can be fully appreciated. The self-tapping thread 14
5 may take any convenient form.
The drill tip 12 of the present invention is formed using radiused
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
10 with their longitudinal axes at equal opposite angles (generally on the
order of 15) with respect to the axis of the blank. Unlike the technique
shown in 3, 933, 075 where the cutters are plunged into the blank with
their axes extending radially there into, to form a uniformly radiused
flute, in forming the flutes 16 and 18 of the screw 10 of the present
15 invention, the cutters are plunged into the blank so that their side edges
impart a straight portion 20 and 22 ~see Fig. 8) to each of the flutes.
Each flute then has a compound configuration which includes a straight
portion 20, 22 and a radiused portion 24, 26. In the preferred embodi-
ment these straight portions 20, 22 include the cutting edges 28 and 30
20 while the radiused portions 24 and 26 include trailing or drag surfaces
32 and 34. The center lines of the cutters are above the end of the
blank 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
~7S~
28 and 30 on the order of thirty degrees. The configuration
of the cutting edges 28, 30 and drag surfaces 32, 34 as they
are seen in Figs. 2 and 3 are necessarily the summation of
the effects of the flutes 16 and 18 and th~ slabbing of heel
portions 38 and 40.
In order to show the actual configuration of the flute
absent the effects of the point, Fig. 8 depicts a cross sec-tion
taken along line 8 - 8 of Fig. 7, a line which is perpendicular
to the axis of flute 16. Flat surface 20 is past, or below the
radial center line Ihereinafter "below center") which is
parallel to the two cutting edges 28 and 30. This is due to
the inclination of the Elutes 16 and 18 relative to the longitud-
inal a~is of the screw. The radiused portion 24 has a uniform
radius of curvature :Ln this plane corresponding to the radius
of the cutter which formed it. Line 8-8 is, of course, not
perpendicular to the axis of flute 18 but is, rather, sloped
at a 30 angle relat:ive thereto. Fig. 8, then, serves as a
dramatic indication of the impact the superposition of the
point can have on the end view of the fastener.
Another feature of the flute configuràtion is shown
in Fig. 6. The intersection of the angulated cut-ters with
the cylindrical periphery of the shank results in curved lead-
ing edges 42 and 44 of the flutes 16 and 18. This, in -
conjunction with the circular configuration of the cutter,
produces a scoop like configuration in the vicini-ty of cutting
edges 28 and 30. This scoop shape, may result in the fastener
pulling itself into the drilled hole, thereby, at least partial-
ly accounting for the fastener's phenomenal drilling capabilities.
One effect of the configurations of heel portions 38 and 40
and flutes 16 and 18 and the scoop-like configuration produced
by the circular configuration of the cutter, as described
above, is the included angle of each of the cutting edges 28
and 30 which is defined respectively by the flutes 16 and 18
and the heel portions 38 and 40 is an acute angle which varies
over the length of the cutting edges 28 and 30 wi-th the most
acute value of that angle occurring at the outermost ends of
cutting edges 28 and 30.
~lthough the preferred embodiment depicts a
conEiguration in which the cutting edges are above
center, it will be appreciated that by
Case No. 3526-00
~5~
decreasing the depth of the cutters' plunge and moving the cutters laterally,
both a below center and ar on center con~ition can be achieved, These
alternate configurations are depicted in Figs. 9 and 1OJ respectively. 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, In these alternative embodiments it is important
to maintain a relatively short chisel length in order to insure that lower
end-pressure is needed to initiate drilling.
Figs. 11 - 13 depict yet another aspect of the present invention.
To dateJ chip-breaking features have only been added to forged-point
drill screws. With the present invention, shallow troughs 46 and 48
extend longitudinally in each milled flute 16 and 18. This chip-breaking
feature is milled by cutter 50 ( F'ig. 13). Cutter 50 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 and an
arcuate rib 56 having a second shorter radius. The rib 56 may be
offset from the axial center line one direction or the other depending
on the flute configuration desired. Although only the above center
configuration has been shown, it will be appreciated that the chipbreaking
trough could also be added to the below center and on center configurations
depicted in Figs. 9 and 10. Further, it will be understood that the cutter
configuration can be modified to move the ribs across the face of the
radiused tooth in order to vary the position of the trough within the flute
to place the chip breaker on either side of the chisel.
As previously mentioned, the end view of the drill screw 10
~ as shown in Figs. 3, 9J 10) and the performance of the screw will vary
10 -
Case No. 3526-00
S6~3~
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 the preferred embodiment and shown
in Fig. 14C consistently outperforms other point geometries when combined
with the flute configuration previously discussed. To form this generally
convex point, a first c~tter ( not shown) having concave teeth is used to
slab off a genera~y 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 the heel portions are each configured by a pair of
planar surfaces 62 and 64 which form an obtuse included angle. The
generally conve~ point of this embodiment is again, formed by a pair
of cutters 66( one of which is shown) which have teeth ~8 having 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 1722 ( as measured internally on the drill screw and
20 externally on the cutter). In this manner, the point formed by surfaces
~2 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. 14B) can be used on this screw as well and may prove advantageous
25 for certain applicationsO
Various changes, modifications and variations will become
apparent to persons of ordinary skill in the art in view of the foregoing
C'ase No. 3526 -00
~5~8i~
diselosure. For example, the generally conve~; point of Fi g. 14C
could have a lesser or greater ineluded angle by shifting the axis
of eutter 58 with respect to the axis of the blank. Further, with
regard to the drill point of the present invention, it is conceivable
the eonfiguration taught herein eould be formed by Eorging. Accord-
ingly, it i8 intended that the present invention eneompass all such
ehanges, modifications and variations as fall within the seope of
the appended claims.
1~ ~
