Note: Descriptions are shown in the official language in which they were submitted.
2052~7
BACKGROUND OF INVENTION
Field of Invention:
This invention relates generally to an anchor which
when installed in a hole drilled in a wall is adapted
to receive a threaded fastener that serves to hold a fixture
or other object against the wall, and more particularly
to a self-drilling anchor of this type which dispenses
with the need for any tool other than a screwdriver to
install the anchor and which is usable with fasteners
~l of different length.
I Status of The Prior Art:
¦ In order to mount brackets, fixtures and other objects
provided with mounting holes against the outer surface
I of a wall formed of plasterboard, sheetrock, fiberboard
I or any other material employed in hollow wall construction,
I the common practice is to use a hollow anchor for this
l purpose. The conventional hollow anchor formed of metal
or plastic, when hammered into and wedged within a hole
I pre-drilled in the wall, is then adapted to receive a
¦ threaded fastener or mounting screw that goes through
the mounting hole in the fixture and turns into the hollow
of the anchor.
The required length of the mounting screw depends
I on the thickness of the fixture or object to be supported
¦ against the wall. Thus if the object is a thin metal
bracket, a screw of smaller length is required than if
the object is a thick plate or board, for this dictates
a longer screw.
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20~2~57
The installation of a conventional anchor entails
three distinct operations, the first and most critical
i step being drilling a hole in the wall, for the diameter
of this hole must be appropriate to that of the anchor.
I Should an oversize hole be drilled, then in the next step
when the anchor is hammered into the hole, the anchor
will not wedge firmly therein but will be somewhat loose.
As a consequence, it will not be possible to carry out
~ the third step.
1 In the third step, one must turn a threaded fastener
~ into the hollow of the anchor, and in doing so tap the
¦ anchor. But if the anchor is somewhat loose in the wall
hole, this will cause the anchor to turn as the fastener
is turned, and the fastener will therefore not be able
to thread its way into the anchor.
There is also a possible fourth step that must be
taken into account; for should a need arise to remove
an object mounted on the wall or replace it with another
, object, then one must first unscrew the fastener from
20 . Il the anchor lodged in the wall. However, if when an unscrewing
;¦ torque is applied to the fastener, this torque causes
¦ the anchor as well as the fastener to turn, then it will
;¦ not be possible to withdraw the fastener from the anchor.
Il The need therefore exists for an anchor which, after being
1 lodged in a hole drilled in the wall, will resist being
¦ turned counterclockwise and thereby make it possible to
unscrew a threaded fastener from the installed anchor.
2052~57
¦ The installation of a conventional hollow anchor
requires three tools: a drill provided with a drill bit
having a diameter appropriate to that of the anchor; a
hammer to drive the anchor in the hole drilled in the
I wall; and a screwdriver to turn the threaded fastener
into the anchor or to later remove it from the anchor.
Though a typical householder or other
non-professional possesses a hammer and a screwdriver,
, he may lack a drill. But even if he has a drill, he may
I not have a drill bit of the appropriate diameter for the
anchor to be installed. Yet there are distinct advantages
to be gained by using hollow wall anchors to mount objects
against a wall, rather than screws, nails or other fasteners
j which require no drilling but which have relatively poor
holding power, particularly in walls made of friable materials.
Nevertheless, the need for drilling has to a significant
degree heretofore discouraged the use of hollow anchors
by non-professionals.
I Though hollow wall anchors are used on a large scale
by professional installers, the need to drill holes and
then hammer the anchors into holes is a practical drawback,
! for these operations are time consuming and hence impose
¦ distinct limits on the number of anchors that can be installed
l¦ in a given period. And if anchors of different sizes
!¦ must be installed, then the installer must change the
¦ drill bit when switching from one anchor size to another,
and this, too, consumes time and reduces the productivity
of the installer.
!
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20~5~7
To overcome these drawbacks, the 1986 patent to
Ernst et al., 4,601,625, discloses an anchor for drywall
that has an externally-threaded cylindrical section adapted
to receive a fastener, and an unthreaded drilling section.
This anchor is installable using only a hand-powered screwdriver
for this purpose, thereby dispensing with the need for
a drill and a hammer. At the upper end of the anchor
~ is a low profile flange or head which allows the anchor
f to be installed flush with the drywall surface.
The Ernst et al. patent discloses an embodiment
or an anchor molded of zinc, and another embodiment formed
of plastic material. Both embodiments include a drill
section that can be deflected laterally upon insertion
I of a mounting screw therethrough. This makes it possible
lS l~ to use a single mounting screw or fastener of moderate
length in conjunction with the anchor for attaching objects
of various thicknesses to the wall. It is also possible
when the need arises to do so, to use longer fasteners.
In Ernst et al., the drill section is formed by
' a single flat blade whose free end is notched to define
~.
a central spike and a pair of peripheral spikes on either
side of the central spike the function of the central
spike, which extends beyond the peripheral spikes and
¦ therefore is the first to penetrate the surface of the
l .g~
1 drywall, is to maintain the location of the rotating drill
I section as a hole is drilled by the peripheral spikes.
In practice, when a single blade is used to bore a hole
in friable material such as drywall, the resultant drilled
hole may not be perfectly round, for when this material
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20~2.~7
60538-1088
encounters the central or gulde splke, lt tends to make the
blade whlp, 8S a consequence of whlch the drllllng ls shlfted
off center and the bored hole is oversl2e or elllptlcal.
In contradlstlnctlon to the cyllndrlcal, externally-
threaded sectlon ln Ernst et al, the shank sectlon of my
prevlous anchor has a root whlch tapers toward the drlll
sectlon and a threadlng surroundlng the root formed by a serles
of convolutlons whose crests are of essentlally the same
dlameter along substantlally the full length of the shank
sectlon. The advantage of thls arrangement ls that as the
anchor ls screwed lnto a wall of frla~le materlal, the
pulverlzed materlal ls then packed by the threadlng lnto a
relatlvely dense mass whlch surrounds the shank to enhance its
reslstance to wlthdrawal from the wall.
And whlle my prevlous self-drllllng anchor also has a
flange-llke head of low proflle slmllar to that of Ernst et al
so that the lnstalled anchor wlll lle flush agalnst the surface
of the wall, ln both cases these self-drllllng anchors when
lnstalled by belng turned lnto a wall do not offer adequate
reslstance to belng turned out. Yet reslstance to belng turned
may be necessary7 for when an occaslon arlseR requlrlng
wlthdrawal of the mountlng screw or fastener from the anchor,
ln turnlng out the fastener wlth a screwdrlver, thls actlon
wlll also cause the anchor to turn out; hence
2~2~7
.1 .
the fastener cannot be withdrawn from the anchor.
ISUMMARY OF INVENTION
IIn view of the foregoing, the main object of this
invention is to provide an improved self-drilling anchor
~ which is installable in a wall by means of a screwdriver,
the anchor being adapted to receive a threaded fastener
that serves to hold a fixture or other object against
the wall, the anchor dispensing with the need for a drill,
;l a hammer, or any tool other than a screwdriver to install
the anchor.
ore particularly an object of this invention is
to provide an anchor of the above type having an
I externally-threaded shank section and a drill section
¦ extending therefrom, which when the anchor is turned into
¦ the wall, the drill section drills a round hole in the
! wall which is then tapped by the threading of the shank
~¦ section.
,¦ A significant feature of the invention resides in
I a threaded anchor having a drill section with multiple
- I cutting blades in which each cutting blade is associated
with a guide blade to ensure that as the drill section
is turned into the wall, the blades proceed to bore a
hold which has a circular cross section and is not off-round
1 or elliptical, thereby ensuring proper thread formation
1 and maximum holding strength when the shank section of
! the anchor taps the hole.
Another feature of the invention resides in a shank
section having a head which when the anchor is installed
is pressed against-the surface of the wall and is provided
with gripping teeth that resist turning out of the anchor.
2~2~57
Hence when it is necessary to unscrew the threaded fastener
from the anchor, this action will not also cause the anchor
I to unscrew from the wall and thereby prevent withdrawal
; of the fastener therefrom.
Also an object of the invention is to provide an
anchor of the above type whose drill section, when forcibly
engaged by the tip of the threaded fastener as it is being
advanced through the shank section, is caused to split
~ open to permit further advance of the fastener, whereby
I the length of the fastener used may greatly exceed that
of the shank section.
¦ A further object of this invention is to provide
¦ a self-drilling anchor having a drill section extending
¦ axially from an externally-threaded shank section, the
I drill section being in the form of a cylindrical core
drill whose bore is aligned with the bore of the shank
section whereby an elongated fastener can pass beyond
the shank section and into and beyond the drill section.
¦ Yet another object of this invention is to provide
~ an anchor of the above type whose shank section has a
tapered root having convoluted threading thereon whose
crests are of essentially the same diameter along substantially
the full length of the shank section, whereby as the anchor
l is turned into a wall of friable material, the resultant
particles are then packed by the threading into a relatively
dense mass which surrounds the shank to enhance its resistance
to withdrawal from the wall.
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2 0 5 2 ~ ~ ~ 60538-1088
Stlll another ob~ect of the lnventlon ls to provlde a
plastlc anchor whlch ls fabrlcated of hlgh strength materlal
and whlch can be manufactured at relatlvely low cost.
Brlefly stated, these ob~ects are attalned ln a self-
drllllng anchor lnstallable ln a wall by means of a screwdrlver
or slmllar tool, the anchor belng adapted to recelve a threaded
fastener that serves to hold a flxture or other ob~ect agalnst
the wall. In one embodlment of the lnventlon, the anchor ln-
cludes an externally-threaded shank sectlon havlng an enlarged
head that ls engageable by the tool. Extendlng from the lower
end of the shank sectlon ls a drlll sectlon that ln one embodl-
ment of the lnventlon ls formed by at least one cuttlng blade
and gulde means whlch are so placed that as the anchor ls turn-
ed lnto the wall by the screwdrlver, the cuttlng blade then
drllls a hole whose wall ls engaged by the gulde means to en-
sure clrcularlty of the hole. And as the anchor contlnues to
turn, the shank sectlon then enters the hole whlch ls tapped by
the threadlng of thls sectlon untll the head engages the outer
surface of the wall to complete the lnstallatlon.
In another embodlment of the lnventlon, the drlll
sectlon ls a core drlll whose blt ls constltuted by one or more
cuttlng teeth, the cyllndrlcal outer surface of the drlll act-
lng as gulde means to ensure the clrcularlty of the drllled
hole.
Thus ln lts broadest sense, the lnventlon seeks to
provlde a self-drllllng anchor lnstallable by means of a
torque-produclng tool ln a hollow wall, sald anchor comprlslng:
(a) an externally-threaded shank sectlon provlded wlth a head
adapted to recelve the tool for turnlng the anchor lnto the
wall, the shank havlng a longltudlnal bore for recelvlng a
fastener to hold an ob~ect; and (b) a drlll sectlon lntegral
,~ ,q,
20~2~S7
. 60538-lOB8
wlth the shank sectlon and extendlng axlally therefrom to drlll
a hole ln the wall whlch 18 tapped by the shank sectlon to
secure the anchor to the wall, the drlll sectlon havlng an open
end and havlng a longltudlnal bore that communicates wlth the
bore of the shank sectlon to permlt the fastener recelved
thereln to advance through and beyond the drlll sectlon, and
havlng at lts open end at least one cuttlng tooth.
~RIEF DESCRIPTION OF DRAWINGS
For a better understandlng of the lnventlon as well
as other obJects and further features thereof, reference ls
made to the followlng detalled descrlptlon to be read ln con-
~unctlon wlth the accompanylng drawlngs, whereln,
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1.
2~25a7
Fig. 1 is a perspective view of a self-drilling
anchor in accordance with the invention;
Fig. 2 is a top view of the anchor:
Fig. 3 is a magnified perspective view of the point
portion of the drill section of the anchor:
Fig. 4 is a transverse section taken through the
drill section of the anchor to show the relationship of
the cutting blades to the guide blades;
Fig. S illustrates the anchor installed in a hollow
I wall, a threaded fastener being received in the anchor
having a length such that it extends the full length of
the shank section, but not beyond:
Fig. 6 shows the installed anchor with a fastener
, whose length is such as to split open the drill section;
~ Fig. 7 is the same as Fig. 6 except that in this
instance, the fastener acts to break off the drill section;
Fig. 8 shows the anchor with the same fastener as
in Fig. 6 in which it splits open the drill section, this
anchor being installed in a double wall;
;I Fig. 9 Ls a perspective view of a self-drilling
anchor having a core drill section in accordance with
the invention;
Fig. 10 is an elevational view of the anchor;
Fig. 11 is a longitudinal section taken through
the anchor;
¦ Fig. 12 is a transverse section taken in the plane
,¦ indicated by line 12-12 in Fig. 11;
Fig. 13 shows the points of the drill section in
relation to the hole to be drilled; and
Fig. 14 shows the anchor installed in a hollow wall,
with a threaded fastener being received in the anchor
whose length is such that it extends beyond the anchor.
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20~2~7
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! DETAILED DESCRIPTION OF INVENTION
The Basic Anchor:
Referring now to Figs. 1 to 4, there is illustrated
in these figures a self-drillng anchor in accordance with
I the invention, the anchor being molded of synthetic plastic
material and having a hollow shank section 10 and a drill
section ll integral therewith.
The synthetic plastic material from which the anchor
I is molded must be of high strength, and when formed to
,¦ create a sharp edge, this edge must be capable of cutting
i the material of the hollow wall in which the anchor is
I installed. The wall is made of plasterboard, sheet rock,
fiberboard and any other material used in hollow wall
l construction. This material is usually friable; that
is to say, it is easily crumbled, and the anchor for this
wall must take this into account.
Preferably, the anchor is molded of nylon reinforced
I with long glass fibers (about 30~ by weight) to provide
¦ a composite which is ductile and therefore moldable at
¦ low cost. The fiberglass constituent of the composite
¦ affords the strength and rigidity required of the anchor
and also effective cutting edges for the drill section.
In practice, the composite material possesses a natural
l or neutral color that will blend with the surface color
1 of the hollow wall.
Hollow shank section 10 is adapted to receive an
externally-threaded fastener or mounting screw to hold
a bracket, a fixture, a board of any other object having
a mounting hole against the surface of the wall in which
¦ the anchor is installed. The length of the fastener is
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I
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20a2~7
¦ appropriate to the thickness of the object to be held.
Shank section 10 has at its upper end an enlarged
head 12 or flange in a low-profile, truncated conical
formation. When the anchor is installed in a hollow wall
~ of plasterboard of other relatively soft material, head
12 will then sink into the wall and lie flush against
its surface.
Formed on the underside of head 12 is a radial array
I of ratchet teeth T whose triangular geometry is such that
when the anchor is turned clockwise into a wall and the
teeth engage its surface, the teeth slip in this direction
and do not impede turning, whereas should one thereafter
seek to turn out the anchor, the teeth will bite into
I the wall to resist counterclockwise movement of the anchor.
I Because of this feature, should the occasion arise when
one wishes to unscrew the threaded fastener from an anchor
installed in a wall, this action will not at the same
time cause the anchor to unscrew from the wall and thereby
, render it difficult if not impossible to remove the fastener
~ ! from the anchor.
¦ Because the flange or head 15 is formed of composite
nylon material having some degree of flexure, the teeth
! T on the underside of the head will yield and not cut
I away the plasterboard or other wall material as the anchor
/1 is being screwed into its final position.
An advantage of an anchor whose head lies flush
against the wall in which the anchor is installed, apart
from the fact that this head does not slightly space the
fixture or other object being mounted from the wall, is
that if the fixture is later removed from the wall, and
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2 0 3 2 ~ ~ 7
one wishes to erase the presence of the anchor, there
is no need to remove the anchor. One has only to spackle
over the head to provide a clean wall surface.
Shank section 10 has a longitudinal cavity 13 therein
having a cruciform formation defining at 90 intervals
ridges R extending the length of the shank section. Ridges
R which surround the central zone of the cavity are capable
of being tapped by the threading of a metal mounting screw
or fastener. One may therefore employ in conjunction
¦ with the anchor mounting screws in a limited range of
,I diameters rather than a screw having a predetermined diameter.
,1 And as will later be explained, the mounting screw may
be much longer than the length of shank section 10, for
the drill section yields to permit the screw to more or
j less extend beyond the shank section to accommodate fixtures
I or other objects of various thicknesses to be mounted
I against the wall.
The cruciform formation of the cavity creates a
socket in head 15 of shank section 10 adapted to receive
0 - ¦ the blade of a Phillips-type screwdriver or of a conventional
screwdriver which is either manually driven or motor powered.
Shank section 10 has a root 14 which is tapered,
i whereas the convolutions of the spiral threading 15 which
1 surrounds the root have crests that are of essentially
5 , the same diameter for the full length of the section except
for the final convolution 15F which is of reduced diameter
to merge with drill section 11 and thereby avoid an abrupt
transition from drill section 11 to shank section 10.
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2~52~57
The relationship of the threading to the root is
such as to cause material which is easily pulverized as
the shank section is turned into the wall, to form a densified
mass surrounding this section to resist withdrawal of
the anchor from the wall.
Drill section 11 is provided with a pair of cutting
blades 16A and 16B which, as best seen in Fig. 4, extend
in opposite directions from the longitudinal axis X of
~ the anchor so that the planar cutting edges E of these
¦ blades are diametrically opposed and act to cut a hole
H in the wall when the anchor is turned. At right angles
to the respective cutting blades is a pair of guide blades
j 17A and 17B which engage the bank of hole H to ensure
I circularity of the hole bored in the wall whereby axis
X of the anchor is colinear with the center axis of the
¦ hole.
The outer ends e of the guide blades are convex
! to conform to the curvature of the bank of the hole and
, to sweep the bank as the drill section is turned. In
~l this way, a round hole is bored into the wall, thereby
¦ avoiding the tendency of a drill section having a single
blade as in the Ernst et al. patent, to cut an oversize
¦ or elliptical hole.
The lower ends of the cutting and guide blades 16A,
~ 16B and 17A, 17B are chamfered. The lower ends of the
cutting blades which are somewhat longer than the guide
I blades define a triangular point P. Thus when the anchor
is pressed into the surface of a wall, point P penetrates
I into the surface. When the anchor is then turned by a
! ' I torque-producing tool, a hole is bored therein by the
cutting blades as guided by the guide blades to ensure
the formation of a round hole.
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In practice, the self-drilling anchor shown in Figs.
1 to 4, instead of being made of synthetic plastic material,
may be fabricated of a corrosion-resistant metal such
as zinc or brass.
Installation:
Referring now to Fig. 5, there is shown an anchor
in accordance with the invention installed in a hollow
wall 18 whose thickness is less than the length of shank
section 10 of the anchor, so that a portion of this section
extends beyond the inner surface of the wall. It will
be seen that low-profile head 15 of the anchor lies flush
with the outer surface of the wall and that the teeth
T on the undersurface of head 15 are embedded in the wall
material to resist turning out of the anchor.
Received in the hollow of shank section 10 is a
mounting screw 19 which holds a fixture 20 against the
surface of the wall, fixture 20 having a mounting hole
21 to admit the screw. The length of mounting screw 19
is such that its tip is received in a conical well 22
at the lower end of the cavity in hollow shank section
- 10 just above the drill section. In practice, the cavity
may be internally-threaded to receive the mounting screw
or it may be unthreaded so that as the mounting screw
I is turned into the cavity, it taps it way therethrough.
1 Because mounting screw 19 fits into the cavity of
¦ the shank section and does not, when fully turned in,
go beyond this section, the integrity of drill section
11 is maintained in the arrangement shown in Fig. 5.
However, in the anchor installation shown in Fig.
I 6, use is made of a much longer mounting screw 23 which
! when turned into shank section 10 forces its way beyond
the well at the lower end of the cavity and in doing so
splits open drill section 11 to permit the mounting screw
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20~2~7
to exit from the shank section. Since the drill section
has already carried out its drilling function, the disruption
of the drill section after drilling is performed does
not interfere with the installation of the anchor. And
since the split drill section is outside of the wall,
it does not affect the holding power of the anchor.
It is to be noted that no notch or indentation is
required in the anchor to facilitate the exit of the mounting
, screw from the shank section, for the tip of the advancing
I mounting screw enters the conical well in the shank section
I cavity and then strikes the drill section at its center
¦ to effect a splitting action in which the two cutting
I blades and their associated guide blades assume a V formation.
I In the anchor shown in Fig. 7, when mounting screw
1 23 is turned into shank section 10, drill section 11,
instead of being split as in Fig. 6, is broken off or
laterally displaced from the shank section. To facilitate
this action, the anchor need not be provided with annular
grooves or notches at the junction of the shank and drill
1I sections, for the natural weakness of this junction causes
¦ the drill section to break off when a force is applied
to this junction by the advancing mounting screw, thereby
permitting the mounting screw to exit from the shank section.
I In practice, the strength of the bridge between the cutting
blades of the drill section will determine when this section
; will spit open and triangulate or break off.
In Fig. 8, the anchor is installed in a double wall
formed by wall 18 superposed on a wall 18' of the same
thickness. Hence in this instance, shank section 10,
when the anchor is installed, does not extend beyond the
I hollow wall but is fully embedded therein. As a consequence,
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20~2~
when drlll section 10 is split open into a V formation,
I the apex portion of the V is lodged in wall 18' and the
¦ wings of the V act as a toggle to resist withdrawal of
~ the anchor from the walls. Thus in a double-wall installation
' which is often used in a high quality commercial construction,
an anchor in accordance with the invention affords enhanced
holding power.
Core Drill Anchor:
Referring now to Figs. 9 to 12, there is shown a reusable
self-drilling anchor in accordance with the invention,
generally designated by numeral 24, which may be molded
of synthetic plastic material, such as Nylon, or of
corrosion-resistant metal, such as zinc. The anchor includes
a hollow shank section 25 having at its upper end an enlarged
lS head 26 or flange in a low-profile, truncated conical
formation. When the anchor is installed in a hollow wall
of plasterboard or other relatively soft material, head
26 will then sink into the wall and lie flush against
its outer surface.
I Formed on the undersurface of head 26 is a radial
¦ array of teeth 27, preferably in a triangular ratchet
formation, so that when the anchor is turned clockwise
into the wall and the teeth then engage its surface, the
~ teeth will slip in this direction and hence not impede
5 ' turning. But should one thereafter seek to turn out the
anchor, such counterclockwise motion will be resisted
, by the teeth.
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2~2~7
Shank section 25 has a longitudinal bore 28 therein
having a cruciform formation defining at 90 intervals
ribs or ridges 28R extending the length of the shank section.
Ridges 28R which surround the central zone of bore 28
are capable of being tapped by the threading of a metal
mounting screw or fastener. One may therefore employ
in conjunction with this anchor, mounting screws in a
limited range of diameters rather than a screw having
a predetermined diameter.
The cruciform formation of the bore creates a socket
I in head 26 of shank section 25 adapted to receive the
! blade of a Phillips-type screwdriver or that of a conventional
screwdriver which is either manually driven or motor powered.
I Shank section 25 has a root 29 which is tapered,
whereas the convolutions of the spiral threading 30 which
surrounds the root have crests that are of essentially
the same diameter for the full length of the section except
for the final convolution, which is of reduced diameter.
As pointed out in connection with the other embodiments
20 ~ of the anchor, the relationship of the threading to the
root is such as to cause wall material which is easily
pulverized as the shank section is turned into the wall,
to form a densified mass surrounding this section to resist
I withdrawal of the anchor from the wall.
25 1 Integral with and extending axially from shank section
¦ 25 is a cylindrical core drill section 31 whose external
¦ diameter matches the external diameter of the tapered
~ root 29 of the shank section at the lowermost end of this
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2~a2~.~7
root. Hence the root of the shank section flows into
the drill section without any discontinuity therebetween.
The longitudinal bore 32 of the drill section is aligned
with the longitudinal bore 28 of the shank section.
The diameter of bore 32 is such as to accommodate
any mounting screw or threaded fastener capable of tapping
the bore 28 of the shank section. As pointed out above,
one does not have to employ with this anchor a fastener
of predetermined diameter, for it is usable with fasteners
1 in a limited range of diameters, as long as the diameter
of the fastener is such that it can pass through the bore
without causing the anchor to expand, rupture or deflect.
iA conventional core drill is a hollow drill that
removes a cylindrical core from the drill hole, the core
drill having a cylindrical bit that functions as the cutting
element of the drill.
In the core drill section 31 in accordance with
the invention, the bit therefor is constituted by a pair
of diametrically-opposed cutting teeth Tl and T2. Each
I tooth is defined by a curved wall having a triangular
form. The inclined edges of the triangle function as
cutting blades and the apex as a sharp spike or point.
Hence when, as shown in Fig. 13, the anchor is pressed
into a typical wall of relatively soft material, the points
Pl and P2 of the core drill section penetrate the wall,
the points being at the poles of the diameter D of the
hole H to be drilled. This diameter is equal to the diameter
of the cylindrical core drill section.
2~rj2~7
The cylindrical exterior surface of the core drill
section acts as guide means to ensure the circularity
of the drilled hole, for as the screwdriver turns the
core drill section into the wall material, the bit teeth
T1 and T2 proceed to cut a round hole whose form is defined
by the cylindrical exterior surface.
After the drill section has drilled a hole in the
wall W, as the anchor continues to be turned by the screwdriver,
the shank section of the anchor then enters this hole,
! and the threading of this section taps the drilled hole,
until, as shown in Fig. 14, the head of the shank section
engages the surface of the wall.
The length of the self-drilling anchor is determined
~ by the thickness of the hollow wall for which it is intended;
lS for when the anchor is being installed, its drill section
31,for most materials~should project from the rear of
the wall before the threads of the shank section engage
and tap the drilled hole. In Fig. 14, the length of the
shank section 25 is longer than the thickness of the wall;
0 - I hence a lower portion of the shank section sticks out
of the wall.
To hold a fixture 33 against the outer surface of
wall W, a threaded fastener 34 is inserted through the
I mounting hole in the fixture into the bore of the shank
5 I section and is screwed therein, the fastener tapping its
way into the bore. The length of fastener 34 is greater
I than that of the anchor; hence as it turns and advances,
I it goes through the bore of the shank section and then
throuqh the bore of the cylindrical core drill section,
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20~2~
the screw then emerging from the drill section, as shown
in Fig. 14.
In this self-drilling anchor, other than the core
of pulverized wall material disposed within the bore of
S the core drill section, there is nothing to impede passage
of the fastener, and as the fastener advances beyond the
shank section, it ejects the core of pulverized material
from the drill section, which is neither deflected nor
split to permit such passage. Hence the integrity of
the anchor is maintained, and should it be later desirable
to unscrew the anchor from the wall, this can ~e done
without difficulty, thereby making it possible to again
use the anchor.
I While there have been shown and described preferred
embodiments of an improved self-drilling anchor in accordance
with the invention, it will be appreciated that many changes
and modifications may be made therein without, however,
departing from the essential spirit thereof. Thus instead
, of the bit of the core drill section being formed by a
- pair of opposed teeth, the bit may be formed by a circular
I array of teeth.
il
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d
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