Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF INVENTION:
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Field of Inven-tion
The present invention relates to a shee-t metal
drill bit for drilling burrless round holes in thin
products, such as metal sheets, plastics, etc., and
wherein the drill bit has a drill head comprised of an
outer cutting edge and a stabilizing central drill bi-t
extending centrally from the front face of the head, and
wherein a concave well is defined between the ou-ter
cutting edge and the central drill bit.
Description of Prior Art
When drilling round holes through a thin layer
of material, such as sheet metal or other type sheet
material, it is common practice today to utilize hole
saws. The drawback of such saws is that they can only
drill holes to a minimum of about 3/4 inch diameter. When
it is necessary to drill smaller holes this may be
achieved by specially designed hole saws which are both
expensive and unserviceable. An alternative method is to
use a conventional fluted drill bit, but these bits wabble
and make holes that are distorted and often with very
sharp burrs on the side edge of the wall and on both sides
of the sheet. It is also known to provide hole cutting
saws with a centrally mounted drill with its cutting end
extending beyond the plane of the circular series of
cutting teeth of an annular tool to guide the annual tool
in a more precise manner. Such a cu-tting saw is disclosed
in U.S. Patent No. 2,926,555.
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SUMMARY OF INVENTION:
It is a feature of the present invention to
provide a novel drill bit for drilling burrless round
holes and which consists of a solid drill body having a
drill head made with a peripheral outer cutting edge and
having a stabilizing central drill bit extending out of
the front face and extending beyond the cutting edge, and
wherein a concave well is defined between the outer
cutting edge and the central drill bit.
Another feature of the present invention is to
provide a drill bit, as above described, and wherein the
drill head has an outer taper for fast clearance~
Another feature of the present invention is to
provide a drill bit, as above described, and wherein the
central drill bit is spring-biased within the drill body.
Another feature of the present invention is to
provide a drill bit, as above described, wherein the
outer cutting edges have a crown which has a small outer
taper to eliminate friction.
Another feature of the present invention is to
provide a drill bit, as above described, wherein the drill
head has an outer taper and wherein there are diagonal
outer cutting edges defining a flute geometry.
According to the above features, from a broad
aspect, the present invention provides a drill bit for
drilling burrless round holes in sheet metal. The drill
bit comprises a solid drill body of circular cross-section
having a drill head and a connecting shaf-t. The drill
head has two diagonally opposed outer cutting edges in a
front face thereof. The cutting edges extend along a
respective opposed circumferential segment of the drill
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head. A stabilizing central drill bit is located in a
central axial bore in the front face and has spring
biasing means to bias a drill end portion of the bit
outwards of the front face to protrude beyond the outer
cutting edges a distance sufficient to penetrate through
sheet metal to be drilled. Each cutting edge has a
leading edge portion which is elevated from the front face
and a downwardly sloping trailing portion. The front face
defines a concave wall between the outer cutting edges and
the central drill bit. The trailing portion extends from
the leading edge to an angulated web portion of the drill
head. The concave wall retains an undrilled sheet metal
piece about the central drill bit whereas said web portion
permits evacuation of loose drilled material during a
drilling process.
BRIEF DESCRIPTION OF DRAWINGS:
A preferred embodiment of the invention will now
be described with reference to the accompanying drawings
in which:
FIGURE 1 is a side view of the improved drill
bit of the present invention;
FIGURE ~ is an exploded side view of the drill
bit;
FIGURE 3 is an enlarged side view of the drill
head; and
FIGURE 4 is a top view of the drill bit.
DESCRIPTION OF PREFERRED EMBODIMENTS:
Referring now to the drawings, and more particu-
larly to Figures 1 and 2, there is shown generally at 10
the drill bit of the present invention for drilling
burrless round holes in sheet metal, plastics sheets, or
other materials. The drlll bit comprises essentially a
solid drill body 11 having a drill head 12 and a connect-
ing shaft 13. The drill head has at least one outer
cutting edge 14, herein two diagonal cutting edges 14 and
14', projecting in a front face 15 thereof. A stabilizing
central drill bit 16 extends from the front face 15 and
projects beyond the outer cutting edges 14 and 14'.
As shown in Figure 2, the solid drill body 11
has a central elongated bore 17 extending in the enlarged
portion 18 for receiving the elongated drill bit 16
therein. A helical spring 19 is located in the cavity or
bore 17 and sits on the bottom wall 20 thereof. A ball
bearing 21 is seated at the top end of the spring 19 to
provide better engagement or seating of the bottom end 22
of the central drill bit 16.
The central drill bit 16 is provided with a
shank end portion 23 having a slotted portion 24 to
receive an arresting end 25 of a set screw 26 which is
threadably engaged in a threaded bore 27 extending trans-
verse to the elongated bore 17 in the drill body 11
whereby to retain the drill bit 16 therein, and cause it
to move axially along the length of the slotted portion
24. The set screw also facilitates insertion and removal
of the drill bit within the bore 17 when it is necessary
to resharpen the cutting edges 14 and 14' of the drill
bit.
Referring now additionally to Figures 3 and 4,
it can be seen that the cutting edges 14 and 14' have an
elevated leading edge portion 28 and a downwardly sloping
trailing portion 29 with an inwardly extending relieved
lip 30. A concave well 31 is defined between the outer
cutting edge 14 and the central drill bit 16. The
relieved lip 30 slopes -to an angulated web portion 32
which follows the curvature of the corresponding cutting
edge 14. This web portion 32 has a concavature and
permits the evacuation of loose drilled material during a
drilling operation through a metal surface. The well
portion 31 serves to retain therein the uncut portion or
an annular disc portion of sheet metal during a drilling
operation.
Because the central drill bit 16 is spring-
biased within the solid drill body 11, very little force
is applied to the drill to do a start-up hole to stabilize
the drill head 12, and substantially only the pressure of
the spring 19 is sufficient to drill -the first hole. As
shown in Fig. 3, the drill 16 protrudes beyond the cutting
edges 14' a distance longer than the thickness of the
material 35. This permits for a more precise positioning
of the stabilizing central drill 16 in a punch hole which
is usually made in the sheet metal surface, as is well
known to a person skilled in the art. Often, when a hole
is drilled a disc of material, such as shown at 35 in
Figure 3, remains embedded within the concave well 31
about the drill bit 16. In order to dislodge this disc
35, the center bit 16 is pushed against a surface offering
resistance to cause the drill bit 16 to retract within the
elongated bore 17 and dislodge itself from the disc 35 and
move behind the disc so as to dislodge the disc from the
concave well 31 by simply ejecting it by the force of the
spring acting on the drill bit 16 now dislodged from the
disc. Thus, the central drill bit also acts as an
ejector.
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As shown more clearly in Figures 3 and 4, the
outer cutting edges 14 and 14' may also be provided with a
small outer taper 34 to eliminate friction of the side
wall 36 of a drill head with the metal piece being drilled
through. This is particularly advantageous when the side
wall of the drill head is a straight side wall, as shown
in Figure 3. However, as shown in Figure 1, the side wall
36 may have an outer taper leading to the cutting edges 14
and 14', and this eliminates friction with the edges of a
drill hole. The inner cutting surface 30 and the inner
well 31 provide a drill head design which eliminates the
formation of burrs occurring on the side edge of the hole
being drilled on both sides of a metal sheet.
It is within the ambit of the present invention
to cover any other obvious modifications, provided such
modifications fall within the scope of the appended
claims.
