U.S. patent application number 12/967831 was filed with the patent office on 2011-04-07 for drill head for deep-hole drilling.
This patent application is currently assigned to Unitac, Inc.. Invention is credited to Takuji Nomura.
Application Number | 20110079445 12/967831 |
Document ID | / |
Family ID | 41444179 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110079445 |
Kind Code |
A1 |
Nomura; Takuji |
April 7, 2011 |
Drill Head for Deep-Hole Drilling
Abstract
Provided is a drill head for deep-hole drilling which does not
generate such a disc that clogs a cutting chip discharge port when
a head main body of the drill head penetrates a work material. The
drill head is mounted with a central cutting blade tip 6 at the
head center portion so as for a blade edge 6a thereof to be
inclined downward toward the head center portion, a circumferential
cutting blade tip 7 at a circumferential portion so as for a blade
edge 7a thereof to be inclined upward toward the head center
portion, and an intermediate cutting blade tip 8 therebetween so as
for a blade edge 8a thereof to be inclined upwardly and inwardly
toward the head center portion, while the cutting blade tips face a
cutting chip discharge port 4 or 5. The drill head includes a head
main body 2 having an interior hollow portion 3 serving as a
cutting chip discharge passage which communicates with the
discharge ports 4 and 5. A disc breaker 12 composed of a surface
inclined downwardly and inwardly toward the head center portion is
formed at a head center side end portion of a flank 8b of the
intermediate cutting blade tip 8.
Inventors: |
Nomura; Takuji; (Hyogo,
JP) |
Assignee: |
Unitac, Inc.
Amagasaki-shi
JP
|
Family ID: |
41444179 |
Appl. No.: |
12/967831 |
Filed: |
December 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2008/072629 |
Dec 12, 2008 |
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12967831 |
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Current U.S.
Class: |
175/412 |
Current CPC
Class: |
B23B 41/02 20130101;
B23B 51/0486 20130101; B23B 2251/422 20130101 |
Class at
Publication: |
175/412 |
International
Class: |
E21B 10/00 20060101
E21B010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2008 |
JP |
2008-162752 |
Claims
1. A deep-hole drilling drill head comprising: a head main body
having a forward end and a rotation axis (G) extending through a
head center portion thereof; at least one cutting chip discharge
port opened at a distal end surface of the head main body; a
central cutting blade tip mounted at the head center portion so as
for a blade edge thereof to be inclined downwardly and inwardly
toward the head center portion; a circumferential cutting blade tip
mounted at a circumferential portion so as for a blade edge thereof
to be inclined upwardly and inwardly toward the head center
portion; an intermediate cutting blade tip mounted between the
central and circumferential cutting blade tips, the intermediate
cutting blade tip having a blade edge inclined upwardly and
inwardly toward the head center portion, the central cutting blade
tip, the circumferential cutting blade tip and the intermediate
cutting blade tip each facing the at least one cutting chip
discharge port; an interior of a hollow portion of the head main
body serving as a cutting chip discharge passage communicating with
the at least one cutting chip discharge port; and a disc breaker
provided at a head center side end portion of a forward facing
flank of the intermediate cutting blade tip, the disc breaker
extending along at least an overlapping region (OL) where the
intermediate cutting blade tip circumferentially overlaps with the
central cutting blade tip, the disc breaker comprising a surface
that is inclined downwardly and inwardly toward the head center
portion.
2. The deep-hole drilling drill head according to claim 1, wherein
the disc breaker forms a first angle (.theta.) with respect to a
plane (Q) orthogonal to the rotation axis (G), said first angle
(.theta.) being in the range of 0 to 60 degrees.
3. The deep-hole drilling drill head according to claim 2, wherein
said first angle (.theta.) is about 20 degrees.
4. The deep-hole drilling drill head according to claim 2, wherein
the upwardly and inwardly inclined blade edge of the intermediate
cutting blade tip forms a second angle (.alpha.) with respect to a
plane (Q) orthogonal to the rotation axis (G), said second angle
(.alpha.) being about 20 degrees.
5. The deep-hole drilling drill head according to claim 1, wherein
the disc breaker extends along an expanded region (M) which
comprises the aforementioned overlapping region (OL) plus an
additional region which extends in a direction away from the head
center portion and the rotation axis G.
6. The deep-hole drilling drill head according to claim 5, wherein,
along the entire expanded region (M), the disc breaker forms a
first angle (.theta.) with respect to a plane (Q) orthogonal to the
rotation axis (G), said first angle (.theta.) being in the range of
0 to 60 degrees.
7. The deep-hole drilling drill head according to claim 6, wherein
the upwardly and inwardly inclined blade edge of the intermediate
cutting blade tip forms a second angle (.alpha.) with respect to a
plane (Q) orthogonal to the rotation axis (G), said second angle
(.alpha.) being about 20 degrees.
8. The deep-hole drilling drill head according to claim 1, wherein:
the forward facing flank of the intermediate cutting blade tip
comprises a major flank surface which is inclined upwardly and
inwardly toward the head center portion, and a minor flank surface
which is inclined downwardly and inwardly toward the head center
portion; the major flank surface is connected to the minor flank
surface at a ridge; and the minor flank surface constitutes the
disc breaker.
9. The deep-hole drilling drill head according to claim 8, wherein:
the major flank surface is associated with the upwardly and
inwardly inclined blade edge; the minor flank surface forms a first
angle (.theta.) with respect to a plane (Q) orthogonal to the
rotation axis (G), said first angle (.theta.) being in the range of
0 to 60 degrees; and the major flank surface forms a second angle
(.alpha.) with respect to a plane (Q) orthogonal to the rotation
axis (G), said second angle (.alpha.) being about 20 degrees.
10. A deep-hole drilling drill head comprising: a head main body
having a forward end and a rotation axis (G) extending through a
head center portion thereof; at least one cutting chip discharge
port opened at a distal end surface of the head main body; a
central cutting blade tip mounted at the head center portion so as
for a blade edge thereof to be inclined downwardly and inwardly
toward the head center portion; a circumferential cutting blade tip
mounted at a circumferential portion so as for a blade edge thereof
to be inclined upwardly and inwardly toward the head center
portion; an intermediate cutting blade tip mounted between the
central and circumferential cutting blade tips, the intermediate
cutting blade tip having a blade edge inclined upwardly and
inwardly toward the head center portion, the central cutting blade
tip, the circumferential cutting blade tip and the intermediate
cutting blade tip each facing the at least one cutting chip
discharge port; an interior of a hollow portion of the head main
body serving as a cutting chip discharge passage communicating with
the at least one cutting chip discharge port; wherein: the
intermediate cutting blade tip has a forward facing flank
comprising: major flank surface associated with the blade edge and
inclined upwardly and inwardly toward the head center portion; and
a minor flank surface connected to the major flank surface and
inclined downwardly and inwardly toward the head center portion,
the minor flank surface being closer to the rotation axis than the
major flank surface; and the minor flank surface constitutes a disc
breaker which extends along at least an overlapping region (OL)
where the intermediate cutting blade tip circumferentially overlaps
with the central cutting blade tip.
11. The deep-hole drilling drill head according to claim 10,
wherein the disc breaker forms a first angle (.theta.) with respect
to a plane (Q) orthogonal to the rotation axis (G), said first
angle (.theta.) being in the range of 0 to 60 degrees.
12. The deep-hole drilling drill head according to claim 11,
wherein said first angle (.theta.) is about 20 degrees.
13. The deep-hole drilling drill head according to claim 11,
wherein the upwardly and inwardly inclined blade edge of the
intermediate cutting blade tip forms a second angle (.alpha.) with
respect to a plane (Q) orthogonal to the rotation axis (G), said
second angle (.alpha.) being about 20 degrees.
14. The deep-hole drilling drill head according to claim 10,
wherein the disc breaker extends along an expanded region (M) which
comprises the aforementioned overlapping region (OL) plus an
additional region which extends in a direction away from the head
center portion and the rotation axis G.
15. The deep-hole drilling drill head according to claim 14,
wherein, along the entire expanded region (M), the disc breaker
forms a first angle (.theta.) with respect to a plane (Q)
orthogonal to the rotation axis (G), said first angle (.theta.)
being in the range of 0 to 60 degrees.
16. The deep-hole drilling drill head according to claim 15,
wherein the upwardly and inwardly inclined blade edge of the
intermediate cutting blade tip forms a second angle (.alpha.) with
respect to a plane (Q) orthogonal to the rotation axis (G), said
second angle (.alpha.) being about 20 degrees.
17. The deep-hole drilling drill head according to claim 10,
wherein: the major flank surface is connected to the minor flank
surface at a ridge.
18. The deep-hole drilling drill head according to claim 10,
wherein: the minor flank surface forms a first angle (.theta.) with
respect to a plane (Q) orthogonal to the rotation axis (G), said
first angle (.theta.) being in the range of 0 to 60 degrees; and
the major flank surface forms a second angle (.alpha.) with respect
to a plane (Q) orthogonal to the rotation axis (G), said second
angle (.alpha.) being about 20 degrees.
Description
RELATED APPLICATIONS
[0001] This is a Continuation-in-Part of International Application
No. PCT/JP2008/072629, filed 12 Dec. 2008 and published as WO
2009/157104 on 30 Dec. 2009, which claims priority to JP
2008-162752, filed 23 Jun. 2008. The contents of the aforementioned
International and priority applications are incorporated by
reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a drill head for deep-hole
drilling in which a central cutting blade tip is mounted at a
center portion, a circumferential cutting blade tip at a
circumferential portion and an intermediate cutting blade tip
therebetween while facing a cutting chip discharge port opened at a
distal end surface of a head main body, and in which an interior of
a hollow portion thereof serves as a cutting chip discharge passage
communicating with the cutting chip discharge port.
BACKGROUND ART
[0003] FIG. 5 illustrates a deep-hole drilling work state by a
conventional deep-hole drilling apparatus. Drilling work is carried
out by coupling a proximal end side of a boring bar 41 which holds
a drill head 31 at a distal end portion thereof to a spindle of a
machine tool or the like via a tool chuck (not shown) to be
rotatingly driven or otherwise rotate a work material W. Herein, a
coolant is supplied in the manner of an external supply system, and
a coolant supply jacket 13 encompassing the hollow boring bar 41
oil-tightly is used. While the jacket 13 is press-contacted with
the work material W via a seal ring 14, the coolant C is supplied
from an introduction port 15 into the jacket 13. The coolant C is
then supplied to a distal end side of a head main body 32 of the
drill head 31 through a gap T between an outer peripheral surface
of the boring bar 41 and an inner circumferential surface of a
cutting hole H. As seen from FIG. 7(a), the coolant C flows from
cutting chip discharge ports 34 and 35 of the head main body 32
(see FIG. 6 and FIG. 7) into a cutting chip discharge passage 40
within the boring bar 41 and is discharged outside, together with
cutting chips S generated in a cutting region. Further, as shown in
FIG. 6 and FIG. 7(a), the head main body 32 is mounted with a
central cutting blade tip 36 at the central portion, a
circumferential cutting blade tip 37 at a circumferential portion
and an intermediate cutting blade tip 38 therebetween, all of which
face the cutting chip discharge ports 34, 35 opened at a distal end
surface 32a. In FIG. 6 and FIG. 7, a reference symbol 16 denotes a
guide pad provided to a distal end side on an outer periphery of
the drill head 31, and a reference symbol 17 denotes a clamp groove
provided slightly near the middle on the same outer periphery of
the drill head 31.
[0004] Supply systems of a coolant to a cutting region include an
internal supply system (double tube system) such as a so-called
ejector system as shown in FIG. 7(b) other than the external supply
system (single tube system) such as a so-called BTA system as shown
in FIG. 5 and FIG. 7(a) as described above. A coolant in the
internal supply system is introduced into a coolant supply passage
40a between outer and inner tubes 42 and 43 at a proximal end side
of a double-tube boring bar 41 as shown by arrows in FIG. 7(b). The
coolant flows outside at a distal end side of the boring bar 41
from a coolant discharge port 46 provided on a circumferential wall
of the drill head 31, thereby being supplied to a cutting region
side. Together with cutting chips S generated in the cutting
region, the coolant is caused to flow from the cutting chip
discharge ports 34 and 35 of the drill head 31 into a discharge
passage 40b composed of the inside of the inner tube 43, and then
the coolant is discharged outside.
[0005] On the other hand, at the time when deep-hole drilling work
of a work material W is carried out by the drill head 31 at the
distal end portion of the boring bar 41 as described above, cutting
chips S of the work material W which are cut by cutting blade tips
36 to 38 are fragmented into pieces smaller than diameters of the
cutting chip discharge ports 34 and 35 of the drill head 31 as
shown in FIG. 7(a) and FIG. 7(b) and flow from the cutting chip
discharge ports 34 and 35 into the inside cutting chip discharge
passage 40 or 40b and then are discharged outside until the drill
head 31 penetrates the work material W. However, at the time when
the drill head 31 penetrates the work material W, that is, when the
drill head 31 cuts and breaks through a distal end wall Wo of the
work material W as shown by virtual lines in FIG. 5, cutting chips
of the work material W having been cut by three of central,
circumferential and intermediate cutting blade tips 36 to 38 of the
drill head 31 become disc-shaped uncut block pieces called discs Sa
to Sd as shown in FIGS. 8(a-1), 8(a-2) to 8(d-1), 8(d-2). The
cutting chips are left at the distal end surface side of the head
main body without being discharged from the cutting chip discharge
ports 34 and 35. It does not much matter when the work material W
comprises a single work material, since the uncut block pieces are
discharged forward and fall from a hole of the penetrated work
material W. On the other hand, there was a problem when a plurality
of work materials W1 to W5 are overlaid and subjected to deep-hole
drilling work as shown in FIG. 9, when attempting to drill a second
work material W2 after a first work material W1 is drilled, discs
Sa to Sd are blocked at an exit of a hole of the first work
material W1 and the cutting chip discharge ports are clogged, which
renders the drilling work unperformable.
[0006] FIG. 8(a-1) and FIG. 8(a-2) are front and cross sectional
views of a conical disc Sa generated by the central cutting blade
tip 36 of the drill head 31 provided with three of central,
circumferential and intermediate cutting blade tips 36 to 38. FIG.
8(b-1) and FIG. 8(b-2) are front and cross sectional views of a
toroidal disc Sc generated by the intermediate cutting blade tip
38. FIG. 8(c-1) and FIG. 8(c-2) are front and cross sectional views
of a larger diameter toroidal disc Sb generated by the
circumferential cutting blade tip 37. FIG. 8(d-1) and FIG. 8(d-2)
are front and cross sectional views of a hat-shaped disc Sd
generated by the central cutting blade tip 36 and the intermediate
cutting blade tip 38 and integrally combined by the disc Sa and the
disc Sc.
[0007] The present invention was made in view of the foregoing
problem, and an object thereof is to provide a drill head for
deep-hole drilling which can fragment cutting chips into small
pieces without generating such a disc that clogs a cutting chip
discharge port when a head main body of the drill head penetrates a
work material, and can discharge the cutting chips from the cutting
chip discharge port reliably.
SUMMARY OF THE INVENTION
[0008] Means for solving the above-described problem will be
described with reference symbols of embodiments which will be
described later. A first aspect of the present invention is a drill
head for deep-hole drilling comprising a head main body 2 having a
rotation axis G extending through a head center portion 24 thereof,
cutting chip discharge ports 4 and 5 opened at a distal end surface
2a of the head main body 2, a central cutting blade tip 6 mounted
at the head center portion so as for a blade edge 6a thereof to be
inclined downwardly and inwardly toward the head center portion, a
circumferential cutting blade tip 7 mounted at a circumferential
portion so as for a blade edge 7a thereof to be inclined upwardly
and inwardly toward the head center portion, an intermediate
cutting blade tip 8 mounted therebetween so as for a blade edge 8a
thereof to be inclined upwardly and inwardly toward the head center
portion, the cutting blade tips facing the cutting chip discharge
port 4, 5, an interior of a hollow portion 3 of the head main body
2 serving as a cutting chip discharge passage communicating with
the cutting chip discharge ports 4 and 5. A disc breaker 12 is
provided at a head center side end portion of a forward facing
flank 8b of the intermediate cutting blade tip 8. The forward
facing flank 8b has a major flank surface 21 which is inclined
upwardly and inwardly toward the head center portion connected to a
minor flank surface 12 which is inclined downwardly and inwardly
toward the head center portion. The minor flank surface 12, which
constitutes the disc breaker 12, comprises a truncated distal end
surface side of the forward facing flank 8b. In one embodiment, the
disc breaker 12 extends along an overlapping region OL where the
intermediate cutting blade tip 8 circumferentially overlaps with
the central cutting blade tip 6. In another embodiment, the disc
breaker 12 extends along an expanded region M which comprises the
aforementioned overlapping region OL plus an additional region
which extends in a direction away from the head center portion and
the rotation axis G.
[0009] A second aspect is characterized in that the disc breaker 12
is inclined at an angle .theta. of between 0 to 60 degrees with
respect to a plane Q orthogonal to a rotation axis G of the head
main body 2, as seen in FIGS. 2(b) and 3.
[0010] Effects by the solving means of the present invention will
be described with reference symbols of embodiments which will be
described later. According to the first aspect of the present
invention, the distal end surface side of the forward facing flank
8b in the overlapping region OL or in the expanded region M is
truncated to form the disc breaker 12 which comprises a surface
that is inclined downwardly and inwardly toward the head center
portion. Thus, particularly the border between a cutting chip which
is cut by the central cutting blade tip 6 and a cutting chip which
is cut by the intermediate cutting blade tip 8 is cut by the disc
breaker 12, whereby uncut block pieces to be formed between
respective cutting blade tips 6 to 8 and a distal end wall portion
of a work material W are fragmented and crushed when the drill head
1 penetrates the work material W. The fragmented and crushed
cutting chips flow from the cutting chip discharge ports 4 and 5
into the interior cutting chip discharge passage 3 and are
discharged outside.
[0011] Accordingly, also in a case where a plurality of work
materials W1 to W5 are overlaid and subjected to deep-hole drilling
work, uncut block pieces to be formed between respective cutting
blade tips 6 to 8 and the distal end wall portion of the work
material W are fragmented and crushed at the time of penetrating
the first work material W1. Since the fragmented and crushed
cutting chips flow from the cutting chip discharge ports 4 and 5
into the interior cutting chip discharge passage 3 and are
discharged outside, clogging of the cutting chip discharge ports 4
and 5 of the head main body 2 is eliminated, and normal cutting is
carried out on and after the second work material. Thus, deep-hole
drilling work of a plurality of overlaid work materials can be
carried out properly.
[0012] The disc breaker 12 is preferably formed into such an
inclined surface that an angle .theta. with respect to a plane Q
orthogonal to a rotation axis G of the head main body 2 in the
overlapping region OL or the expanded region M is in the range of 0
to 60 degrees as in the second aspect of the present invention.
When the angle is below 0 degrees, that is, a negative angle, the
border between the cutting chip which is cut by the central cutting
blade tip 6 and the cutting chip which is cut by the intermediate
cutting blade tip 8 is resistant to cutting, and there is a concern
of not serving the role as the disc breaker 12. When the angle
.theta. exceeds 60 degrees, a peripheral edge of the disc breaker
12 becomes too acute and may possibly be damaged.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1(a) is a front view showing a drill head for deep-hole
drilling according to the present invention, and FIG. 1(b) is a
plan view thereof.
[0014] FIG. 2(a) is an enlarged partial view of FIG. 1(a), and FIG.
2(b) is a further enlarged partial view thereof.
[0015] FIG. 3 is an enlarged partial view showing another
embodiment of a disc breaker according to the present invention,
similar to FIG. 2(b).
[0016] FIG. 4(a) is a perspective view showing the drill head
according to the present invention, and FIG. 4(b) is a perspective
view showing a conventional drill head.
[0017] FIG. 5 is a longitudinal sectional view showing a deep-hole
drilling work state by a deep-hole drilling apparatus provided with
the conventional drill head.
[0018] FIG. 6 is a plan view showing the conventional drill
head.
[0019] FIG. 7 shows the conventional drill head during deep-hole
drilling work by a deep-hole drilling apparatus provided with the
conventional drill head, and FIG. 7(a) is a cross sectional view
along an axis direction in a coolant external supply system and
FIG. 7(b) is a cross sectional view along an axis direction in a
coolant internal supply system.
[0020] FIG. 8 shows uncut block pieces called discs which are
formed by cutting blade tips of the drill head when the drill head
penetrates a work material, and FIGS. 8(a-1) to 8(d-1) are front
views and FIGS. 8(a-2) to 8(d-2) are cross sectional views.
[0021] FIG. 9 is a cross sectional view of a state where a
plurality of work materials are overlaid and subjected to deep-hole
drilling work.
DESCRIPTION OF REFERENCE SYMBOLS
[0022] 1: Drill head [0023] 2: Head main body [0024] 2a: Distal end
surface of head main body [0025] 3: Hollow portion of head main
body (cutting chip discharge passage) [0026] 4, 5: Chip discharge
port [0027] 6: Central cutting blade tip [0028] 7: Circumferential
cutting blade tip [0029] 8: Intermediate cutting blade tip [0030]
8a: Blade edge [0031] 8b: Flank [0032] 8c: Cutting Face [0033] 12:
Minor flank surface or Disc breaker [0034] 21: Major flank surface
[0035] 22: Forward end of head main body [0036] 23: Ridge [0037]
24: Head center portion
DETAILED DESCRIPTION
[0038] Hereinafter, preferred embodiments of the present invention
will be described based on the drawings. FIG. 1(a) is a front view
showing a drill head 1 for deep-hole drilling according to the
present invention, and FIG. 1(b) is a plan view thereof. FIG. 2(a)
is an enlarged partial view of FIG. 1(a), and FIG. 2(b) is a
further enlarged partial view thereof. FIG. 3 is an enlarged
partial view showing another embodiment of the present invention,
similar to FIG. 2(b). FIG. 4(a) is a perspective view showing the
drill head 1 according to the present invention, and FIG. 4(b) is a
perspective view showing a conventional drill head. In FIG. 4(a),
the drill head 1 for deep-hole drilling includes a substantially
cylindrical head main body 2 having a distal end side formed into a
substantially obtuse conical shape. An interior of the head main
body 2 forms a hollow portion 3 (FIG. 1) and a lower end side of
the head main body 2 is opened entirely.
[0039] The substantially obtuse conical distal end surface 2a of
the head main body is formed with a large and a small cutting chip
discharge port 4 and 5 radially opposed to each other and
communicating with the hollow portion 3. At an opening edge along a
head diameter direction of the large cutting chip discharge port 4,
the central cutting blade tip 6 and the circumferential cutting
blade tip 7 are brazed to depressions 9 to 11 provided to the head
respectively, whereas at an opening edge along the head diameter
direction of the small cutting chip discharge port 5, the
intermediate cutting blade tip 8 is brazed to depressions 9 to 11
provided to the head.
[0040] As shown in FIG. 1(a), FIG. 2 and FIG. 4(a), the central
cutting blade tip 6 is mounted so as for a blade edge 6a thereof to
be inclined downwardly and inwardly toward the head center portion
24. Thus, a forward facing flank 6b is also inclined downwardly and
inwardly toward the head center portion 24. The circumferential
cutting blade tip 7 is mounted so as for a blade edge 7a thereof to
be inclined upwardly and inwardly toward the head center portion
24, and thus a forward facing flank 7b is also inclined upwardly
and inwardly toward the head center portion 24. The intermediate
cutting blade tip 8 is mounted so as for a blade edge 8a thereof to
be inclined upwardly and inwardly toward the head center portion 24
in the same manner as the circumferential cutting blade tip 7, and
thus a major flank surface 21 of a forward facing flank 8b is also
inclined upwardly and inwardly toward the head center portion 24.
In FIG. 2 and FIG. 3, reference symbols 6c, 7c and 8c denote
cutting faces, and reference symbols 6d, 7d and 8d denote cutting
chip breakers. Further, in FIGS. 1 to 3, reference symbol G denotes
a rotation axis of the head main body 2.
[0041] At its forward end 22, the drill head 1 according to the
present invention is characterized by the intermediate cutting
blade tip 8 having a forward facing flank 8b, the forward facing
flank 8b comprising a major flank surface 21 associated with the
blade edge 8a connected to a minor flank surface 12, the minor
flank surface 12 being closer to the rotation axis G than the major
flank surface 21 and serving as a disc breaker 12. The disc breaker
12 constitutes a truncated portion of the forward facing flank 8b
along at least an overlapping region OL where the intermediate
cutting blade tip 8 circumferentially overlaps with the central
cutting blade tip 6. The disc breaker 12 comprises a surface that
is inclined downwardly and inwardly toward the head center portion
24, at a head center side end portion of the forward facing flank
8b of the intermediate cutting blade tip 8 whose major flank
surface 21 is inclined upwardly and inwardly toward the head center
portion 24, as seen from FIG. 2(a) and FIG. 2(b). In FIG. 2(b), the
truncated region of the intermediate cutting blade tip 8 is filled
in with black and denoted by symbol K. More accurately, the term
disc breaker is used for convenience by the present applicant in
order to precisely represent a role as a breaker of transversely
fragmenting and crushing discs Sa to Sd (FIG. 8) which are
disc-shaped uncut block pieces formed by the central cutting blade
tip 6, circumferential cutting blade tip 7, and intermediate
cutting blade tip 8.
[0042] Thus, the forward facing flank 8b of the intermediate
cutting blade tip 8 comprises a major flank surface 21 which is
inclined upwardly and inwardly toward the head center portion 24
and a minor flank surface 12 which is inclined downwardly and
inwardly toward the head center portion 24, the minor flank surface
serving as the disc breaker. The major flank surface 21 and the
minor flank surface 12 meet at a ridge 23.
[0043] In this embodiment, the disc breaker 12 comprises an
inclined surface having an angle .theta. of 20 degrees with respect
to a plane Q orthogonal to the rotation axis G of the head main
body 2 in the afore-described overlapping region OL as shown in
FIG. 2(b). In this case, an angle .alpha. between the blade edge 8a
which is inclined upwardly and inwardly toward the head center
portion 24 and the orthogonal plane Q is 20 degrees.
[0044] In the embodiment shown in FIGS. 2(a) and 2(b), the forward
facing flank 8b of the intermediate cutting blade tip 8 is
truncated only in the overlapping region OL where the intermediate
cutting blade tip 8 circumferentially overlaps with the central
cutting blade tip 6, to form the disc breaker 12.
[0045] However, the disc breaker 12 according to the present
invention is not restricted only to the overlapping region OL. The
disc breaker 12 can comprise a surface that extends beyond the
overlapping region OL in a direction away from the head center
portion 24. Such an embodiment is shown in FIG. 3. In the
embodiment shown in FIG. 3, the disc breaker 12 extends into an
expanded region M which comprises the aforementioned overlapping
region OL along with a further region which extends in a direction
away from the head center portion 24 and the rotation axis G. The
further region may, for example, be about a half to a third of a
width of the overlapping region OL). In the expanded region M, the
disc breaker 12 again comprises a surface that is downwardly
inclined toward the head center portion 24 from the upwardly
inclined major flank surface 21 of the forward facing flank 8b of
the intermediate cutting blade tip 8.
[0046] In the embodiment shown in FIG. 3, along the entire length
of the region M, the downwardly and inwardly inclined disc breaker
12 forms an angle .theta. with respect to the plane Q orthogonal to
the rotation axis G of the head main body 2. In one embodiment,
angle .theta. is about 20 degrees. As also seen in the embodiment
of FIG. 3, the upwardly and inwardly inclined blade edge 8a of the
intermediate cutting blade tip 8 and the orthogonal plane Q form an
angle .alpha., which in one embodiment is about 20 degrees.
[0047] FIG. 4(b) shows a conventional drill head 31. As seen from a
comparison with the drill head 1 according to the present
invention, the central cutting blade tip 36 and the circumferential
cutting blade tip 37 of the conventional drill head 31 are of the
same structure with the central cutting blade tip 6 and the
circumferential cutting blade tip 7 of the drill head according to
the present invention, respectively. However, the intermediate
cutting blade tip 38a is formed such that a blade edge 38 and flank
38b thereof are upwardly inclined upward from a head periphery end
portion to a head center side end portion. As seen from reference
to FIG. 2(b), the truncated region K at the distal end surface side
of the region OL where the intermediate cutting blade tip 8
circumferentially overlaps with the central cutting blade tip 6 is
left as is. Accordingly, the cutting chip Sa cut by the central
cutting blade tip 6 and the cutting chip Sc cut by the intermediate
cutting blade tip 8 are connected in the remaining region K (FIG.
2(b)) and cannot be broken off.
[0048] As a result, cutting chips of the work material W cut by the
central, circumferential and intermediate cutting blade tips 36 to
38 of the conventional drill head 31 become uncut block pieces
called discs Sa to Sd as shown in FIG. 8 when the drill head 31
penetrates the work material W, that is, when the drill head 31
cuts and breaks through a distal end wall portion Wo of the work
material W as shown by virtual lines in FIG. 5. Consequently, the
cutting chips are left at the distal end surface side of the head
main body without being discharged from the cutting chip discharge
ports 34 and 35. It does not matter as much when the work material
W comprises work material having unitary one-piece construction,
since the cutting chips are discharged forward and fall from the
far end of a hole formed in the penetrated work material W. On the
other hand, drilling work becomes impossible when a plurality of
work materials W1 to W5 are overlaid and subjected to deep-hole
drilling work as shown in FIG. 9, since the discs Sa to Sd are
blocked at an exit of a hole of a first work material W1 and the
cutting chip discharge ports are clogged when attempting to drill a
second work material W2 after the first work material W1 is
drilled.
[0049] According to the drill head 1 of the present invention, the
intermediate cutting blade tip 8 has a forward facing flank 8b
comprising a major flank surface 21 which is upwardly inclined
towards the head center portion 24 and connects to a disc breaker
12 (minor flank surface) which is downwardly inclined towards the
head center portion 24. The disc breaker 12 extends on the head
center portion side of the intermediate cutting blade tip 8 along
either just the overlapping region OL (embodiment of FIGS. 2(a) and
2(b)), or in the region M which includes the region OL and a
further region extending in a direction away from the head center
portion 24 and the rotation axis G. Therefore, the border between
the cutting chip which is cut by the central cutting blade tip 6
and the cutting chip which is cut by the intermediate cutting blade
tip 8 is cut by the disc breaker 12, and so is the border between
the cutting chip which is cut by the central cutting blade tip 8
and the cutting chip which is cut by the circumferential cutting
blade tip 7. As a result, uncut block pieces to be formed between
respective cutting blade tips 6 to 8 and the distal end wall
portion of the work material W are fragmented and crushed when the
drill head 1 penetrates the work material W. The fragmented and
crushed cutting chips flow from the cutting chip discharge ports 4
and 5 into the interior cutting chip discharge passage 3 to be
discharged outside.
[0050] Accordingly, even when a plurality of work materials W1 to
W5 are overlaid and subjected to deep-hole drilling work as shown
in FIG. 9, uncut block pieces to be formed between respective
cutting blade tips 6 to 8 and the distal end wall portion of the
work material W are fragmented and crushed at the time of
penetrating the first work material W1. The fragmented and crushed
cutting chips flow from the cutting chip discharge ports 4 and 5
into the interior cutting chip discharge passage 3 and are
discharged outside. As a result, clogging of the cutting chip
discharge ports 4 and 5 of the head main body 2 is eliminated, and
normal cutting is carried out on and after the second work
material. Thus, deep-hole drilling of a plurality of overlaid work
materials can be performed properly.
[0051] The afore-described inclined disc breaker 12 is preferably
formed such that an angle .theta. with respect to the plane Q
orthogonal to the rotation axis G of the head main body 2 is in the
range of 0 to 60 degrees. When the angle .theta. is below 0
degrees, that is, a negative angle, the border between the cutting
chip which is cut by the central cutting blade tip 6 and the
cutting chip which is cut by the intermediate cutting blade tip 8
is resistant to cutting, and there is a concern of not serving the
role as the disc breaker 12. When the angle .theta. exceeds 60
degrees, a periphery edge side of the disc breaker 12 becomes too
acute and may possibly be damaged.
* * * * *