Cutting by use of rotating axially moving tool – Plural tool-assemblages – Coaxial
Reexamination Certificate
2002-02-26
2003-10-28
Bishop, Steven C. (Department: 3722)
Cutting by use of rotating axially moving tool
Plural tool-assemblages
Coaxial
C408S229000
Reexamination Certificate
active
06637989
ABSTRACT:
TECHNICAL FIELD
This invention relates to improvements in cutting tools and, in particular, to a cutting tool with an opening that facilitates accurate positioning of the axis of rotation of a cutting tool drilling a hole in a work piece.
BACKGROUND OF THE INVENTION
Conventional tools, such as drill bits, for cutting holes in a work piece have pointed tips that position the axes of rotation of the drill bits at the locations of the centers of the holes to be drilled. However, a drill bit with a pointed tip and no means to ensure lateral stability tends to wander as the drill bit finds the center of the hole and thereby exerts a lateral force against its side wall. The result is a drilled hole of nonuniform diameter along its length, which prohibits a drill operator from drilling a pair of side-by-side holes with a thin partition between them. Drill bits of the type described in U.S. Pat. No. 5,832,720 do not suffer from lateral instability and are, therefore, capable of drilling dimensionally accurate, smooth-sided holes in work pieces.
FIGS. 1-5
show several views of a prior art cutting tool described in U.S. Pat. No. 5,832,720, in which a circular hole drill bit
10
comprises a cylindrical body
12
having a driver engaging end
14
opposite a work engaging end
16
. A substantially cylindrical side wall
18
extends between driver engaging end
14
and work engaging end
16
. Body
12
is adapted to be rotated about an axis of rotation
22
relative to a work piece in a predetermined direction indicated by a counterclockwise pointing arrow
20
when working. Work engaging end
16
may comprise a work end face
21
that is substantially flat (
FIG. 1
) or stepped (
FIG. 1A
) at work engaging end
16
. Body
12
is formed with an elongate flute
24
in side wall
18
, extending from work end face
21
towards driver engaging end
14
in a direction generally parallel to axis of rotation
22
. At work end face
21
, flute
24
has a minimum depth that is equal to the radius R of shaft
12
. Flute
24
has a trailing face
30
with respect to direction
20
of rotation of bit
10
when rotated in its work direction. (
FIG. 1A
shows a flute
24
having a sharp corner at the step formation of face
21
.)
Formed on work engaging end
16
of drill bit
10
is a cutting tooth
32
that is configured to have a cutting edge
34
and a guide projection
35
that extends laterally of side wall
18
. Cutting edge
34
extends from axis
22
and along the portion of guide projection
35
nearer to work engaging end
16
. Cutting edge
34
is also positioned above end face
21
as shown in
FIGS. 1 and 4
, so that cutting edge
34
may engage the work piece when drill bit
10
is rotated. Cutting edge
34
may extend perpendicularly to axis of rotation
22
, in which instance cutting edge
34
terminates at axis
22
, or cutting edge
34
may be inclined upwardly as is shown in
FIG. 1
from axis
22
toward side wall
18
, in which instance cutting edge
34
can extend beyond axis
22
. In this latter instance, relief is provided on end face
21
at axis
22
so that the portion of cutting edge
34
extending beyond axis
22
does not counteract the hole cutting operation, as shown in
FIGS. 1 and 2
.
Guide projection
35
is formed with a guide face
50
that is concentric with axis
22
and intersects cutting edge
34
to form a sharp corner. Guide face
50
is spaced from axis
22
by an amount greater than the spacing of any other part of body
12
, so that in rotation of drill bit
10
no portion of body
12
will engage the side wall of the hole formed in the work piece by drill bit
10
. As a practical matter, the spacing should be slightly greater than the eccentricity, colloquially known as “slop,” in the rotation of the chuck holding the drill bit, which eccentricity results from slack in the mounting of the chuck in the driving mechanism. The guide projection distance from side wall
18
is also determined by the properties of the drill bit material—the harder the drill bit material, the greater the possible guide projection distance without flexure of drill bit
10
. Normally the guide projection distance from side wall
18
in a drill bit of 1 to 1¼ inches (2.5-3.2 centimeters) in diameter will be between about 0.001-0.250 inch (0.025-6.4 millimeters).
In the direction parallel to axis
22
, guide face
50
preferably has a minimum length, L, equal to the depth of the cut made by cutting edge
34
in about one and one-half revolutions of the drill bit. This may be from 0.001-0.500 inch (0.025-12.7 millimeters) depending on the material being cut. In the circumferential direction, guide face
50
preferably also has a length of no less than the depth of cut. Guide face
50
preferably is maintained at a minimum size so as to minimize the area of contact with the work piece, thereby minimizing the amount of heat generated to not appreciably increase the temperature of the finished surface and to keep drill bit
10
cool. Cutting tooth
32
rearwardly of guide face
50
is tapered inwardly toward side wall
18
leaving enough material to support guide projection
35
. This inward taper provides for guide face
50
relief that prevents scoring of the finished surface of the work piece by side wall
18
as drill bit
10
advances into the work piece to remove material from it.
When drill bit
10
is to be used to cut through layers of a composite work piece of different degrees of solidity or hardness (e.g., fibrous material and solid material layers), the length L is preferably chosen to be longer than the depth of cut achievable by at least one revolution of drill bit
10
in each of two adjacent layers so that guide projection
35
concurrently contacts the two adjacent layers while cutting through the transition line between them. This is to ensure layer-to-layer overlap of guide projection
35
and thereby prevent deflection of the cutting path of drill bit
10
at the transition between adjacent work piece layers.
FIG. 2A
is an end view of an alternative circular hole drill bit
10
a
, which differs from drill bit
10
in that drill bit
10
a
has multiple guide projections
35
a
,
35
b
,
35
c
, and
35
d
concentric with axis
22
a
with equal radii extending and uniformly spaced apart around the periphery of side wall
18
a
at work end face
21
a
to facilitate cutting through layers of a composite work piece of different degrees of solidity or hardness. Drill bit
10
a
rotates in direction
20
a
about axis
22
a
to cut a hole in the work piece.
FIG. 2B
is a fragmentary sectional view showing drill bit
10
a
cutting into a layer of a multiple-layer work piece. The formation of guide projections
35
a
,
35
b
,
35
c
, and
35
d
on side wall
18
a
is analogous to the formation of guide projection
35
on side wall
18
, except as indicated below. Guide projections
35
a
,
35
b
,
35
c
, and
35
d
reduce the propensity of side wall
18
a
to flex laterally as drill bit
10
a
passes through a softer material to a harder material and thereby maintain a uniform hole diameter through the multiple layers of a work piece. Although
FIG. 2A
shows guide projections
35
a
,
35
b
,
35
c
, and
35
d
at 90 degree angularly displaced locations, the number and angular separation of the guide projections can be selected depending on the properties of a work piece that would induce body flexure of the drill bit.
When formed of ordinary tool steel, drill bit
10
is particularly suited for the drilling of holes in wood, soft metals, such as aluminum and brass, and plastics, such as delrin™ and nylon™, and other like materials. The hole drilled can have a flat bottom (depending on the inclination of cutting edge
34
from axis
22
to side wall
18
), will have an exceptionally smooth side wall, and will be accurately dimensioned. If cutting tooth
32
is formed of a harder material, such as a carbide, drill bit
10
can be used in harder metals, glass, porcelain, and other hard materials.
The cutting tool formed as a drill bit without a pointed tip as taught in
Bishop Steven C.
Bitmoore
Stoel Rives LLP
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