U.S. patent application number 12/903789 was filed with the patent office on 2011-03-24 for drill head for deep-hole drilling.
This patent application is currently assigned to Unitac, Inc.. Invention is credited to Takuji Nomura.
Application Number | 20110067927 12/903789 |
Document ID | / |
Family ID | 41198895 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110067927 |
Kind Code |
A1 |
Nomura; Takuji |
March 24, 2011 |
Drill Head for Deep-Hole Drilling
Abstract
Provided is a drill head for deep-hole drilling in which a
cutting blade tip is mounted to face a cutting chip discharge port
opened at a head distal end surface and a hollow inside is made
into a cutting chip discharge passage communicating with the
cutting chip discharge port, wherein high cutting efficiency based
on good cutting chip dischargeability can be achieved and the
cutting blade itself is also easily processed in terms of form. The
drill head for deep-hole drilling is configured such that an inner
end 20a of a blade edge 20 of a center cutting blade tip 2A is
spaced apart from a head shaft center axis O and forms a
non-cutting zone Z in the vicinity of the head shaft center axis O,
an inner side surface of the cutting blade tip 2A constitutes an
axially rearwardly inclined side surface 21 inclined from an inner
end side to the head shaft center axis O side, an uncut core C of a
work material W generated in the non-cutting zone Z is broken off
by press-contact of the inclined side surface 21 of the cutting
blade tip 2A during deep-hole drilling work.
Inventors: |
Nomura; Takuji; (Hyogo,
JP) |
Assignee: |
Unitac, Inc.
Amagasaki-shi
JP
|
Family ID: |
41198895 |
Appl. No.: |
12/903789 |
Filed: |
October 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2008/072627 |
Dec 12, 2008 |
|
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12903789 |
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Current U.S.
Class: |
175/404 |
Current CPC
Class: |
B23B 51/0486 20130101;
B23B 2240/08 20130101; B23B 2251/422 20130101; B23B 2251/46
20130101 |
Class at
Publication: |
175/404 |
International
Class: |
E21B 10/00 20060101
E21B010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2008 |
JP |
2008-104474 |
Claims
1. A drill head for deep-hole drilling, comprising: a head main
body having a head shaft center axis (O) defining a forward-to-rear
axial direction; a head distal end surface provide at a forward end
of the head main body; one or more cutting blade tips mounted on
the head main body and positioned to face a cutting chip discharge
port opened at the head distal end surface; and a hollow portion
constituting a cutting chip discharge passage which communicates
with the cutting chip discharge port; wherein: at least one of said
one or more cutting blade tips serves as a center cutting blade tip
which is responsible for cutting a center portion of a hole, the
center cutting blade tip comprising: a blade edge having an inner
end spaced apart from the head shaft center axis of the head main
body, whereby the inner end forms a non-cutting zone in the
vicinity of the head shaft center axis upon rotation of the drill
head during drilling operations; and an inner side surface at an
inner end side of the blade edge, the inner side surface having an
axially rearwardly inclined surface which is inclined from the
inner end to the head shaft center axis side; wherein the axially
rearwardly inclined surface of the cutting blade inner side surface
is configured to press-contact and break off an uncut core
generated in the non-cutting zone upon rotation of the gun drill
during drilling operations.
2. The drill head for deep-hole drilling according to claim 1,
wherein: the axially rearwardly inclined surface of the center
cutting blade tip forms an angle of 75 to 90 degrees with respect
to a tip front surface.
3. The drill head for deep-hole drilling according to claim 1,
wherein: the center cutting blade tip has an inner end of a blade
edge spaced 0.05 to 0.5 mm apart from the head shaft center axis;
and an inclination angle of the inclined side surface with respect
to the head shaft center axis is 5 to 30 degrees.
4. The drill head for deep-hole drilling according to claim 1,
wherein the center cutting blade tip has a blade edge arranged in
parallel with a radial line passing through the head shaft center
axis and in a center-raised position 0.2 to 1.5 mm more forward in
a cutting rotation direction than the radial line.
5. The drill head for deep-hole drilling according to claim 1,
wherein the at least one or more cutting blade tips is brazed to a
recessed portion provided to the head main body.
6. The drill head for deep-hole drilling according to claim 1,
wherein: the whole of the blade edge of the center cutting blade
tip is inclined in a radially inward and axially forward direction
towards the head shaft center axis side; and a guide pad is
provided on a head outer circumferential surface at a position
opposite to a mounting side of the center cutting blade tip.
7. The drill head for deep-hole drilling according to claim 1,
wherein: the whole of the blade edge of the center cutting blade
tip is inclined in a radially inward and axially forward direction
toward the head shaft center axis side.
8. The drill head for deep-hole drilling according to claim 1,
wherein: the inner end constitutes the forwardmost portion of the
drill head.
9. The drill head for deep-hole drilling according to claim 1,
wherein: the head shaft center axis intersects the axially
rearwardly inclined surface of the center cutting blade tip.
10. The drill head for deep-hole drilling according to claim 1,
wherein: the whole of the blade edge of the center cutting blade
tip is inclined in a radially inward and axially forward direction
toward the head shaft center axis side. the inner end constitutes
the forwardmost portion of the cutting head; and the head shaft
center axis intersects the axially rearwardly inclined surface of
the center cutting blade tip.
11. The drill head for deep-hole drilling according to claim 10,
wherein: a guide pad is provided on a head outer circumferential
surface at a position opposite to a mounting side of the center
cutting blade tip; the center cutting blade tip is brazed to a
recessed portion of the cutting head; and the cutting blade tip and
the guide pad are devoid of clamping bores suitable for receiving a
clamping screw.
12. The drill head for deep-hole drilling according to claim 1,
further comprising: a circumferential cutting blade tip and an
intermediate cutting blade tip, both of which are radially outward
of the center cutting blade tip; wherein: the circumferential
cutting blade tip, the intermediate cutting blade tip and the
center cutting blade tip are all brazed to respective recessed
portions of the drill head; and the circumferential cutting blade
tip, the intermediate cutting blade tip and the center cutting
blade are all devoid of clamping bores suitable for receiving a
clamping screw.
13. The drill head for deep-hole drilling according to claim 1,
wherein: the center cutting blade tip is the only blade tip on the
drill head; and the center cutting blade tip is retained to the
drill head by a clamping screw.
14. A drill head for deep-hole drilling comprising: one or more
cutting blade tips mounted to face a cutting chip discharge port
opened at a head distal end surface; and a hollow inside made into
a cutting chip discharge passage communicating with the cutting
chip discharge port; wherein: a center cutting blade tip, which is
responsible for cutting a center portion of a hole, has an inner
end of a blade edge spaced apart from a head shaft center axis, the
inner end positioned to form a non-cutting zone in a vicinity of
the shaft center axis; an inner side surface of the cutting blade
tip constitutes an axially rearwardly inclined surface which is
inclined from the inner end to the head shaft center axis side, and
the axially rearwardly inclined surface is configured to
press-contact and break off an uncut core of a work material
generated in the non-cutting zone during deep-hole drilling
work.
15. The drill head for deep-hole drilling according to claim 14,
wherein: the axially rearwardly inclined surface of the center
cutting blade tip forms an angle of 75 to 90 degrees with respect
to a tip front surface.
16. The drill head for deep-hole drilling according to claim 14,
wherein: the center cutting blade tip has an inner end of a blade
edge spaced 0.05 to 0.5 mm apart from the head shaft center axis;
and an inclination angle of the inclined side surface with respect
to the head shaft center axis is 5 to 30 degrees.
17. The drill head for deep-hole drilling according to claim 14,
wherein the center cutting blade tip has a blade edge arranged in
parallel with a radial line passing through the head shaft center
axis and in a center-raised position 0.2 to 1.5 mm more forward in
a cutting rotation direction than the radial line.
18. The drill head for deep-hole drilling according to claim 14,
wherein the at least one or more cutting blade tips is brazed to a
recessed portion provided to a head main body.
19. The drill head for deep-hole drilling according to claim 14,
wherein: the whole of the blade edge of the center cutting blade
tip is inclined in a radially inward and axially forward direction
towards the head shaft center axis side; and a guide pad is
provided on a head outer circumferential surface at a position
opposite to a mounting side of the center cutting blade tip.
20. The drill head for deep-hole drilling according to claim 14,
wherein: the whole of the blade edge of the center cutting blade
tip is inclined in a radially inward and axially forward direction
toward the head shaft center axis side. the inner end constitutes
the forwardmost portion of the cutting head; and the head shaft
center axis intersects the axially rearwardly inclined surface of
the center cutting blade tip.
Description
RELATED APPLICATIONS
[0001] This is a continuation-in-part of international application
no. PCT/JP2008/072627, filed 12 Dec. 2008, which published as WO
2009/128183A1 and claims priority to JP2008-104474, filed 14 Apr.
2008. The contents of the aforementioned applications are
incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a drill head for deep-hole
drilling in which a cutting blade tip is mounted to face a cutting
chip discharge port opened on a head distal end surface and in
which a hollow inside is made into a cutting chip discharge passage
communicating with the cutting chip discharge port.
BACKGROUND
[0003] As this kind of drill head for deep-hole drilling, ones as
shown in FIG. 9 and FIG. 10 have been widely used conventionally. A
drill head 50A in FIG. 9 has a substantially cylindrical head main
body 51 with a hollow portion 52 opened at a proximal end side and
a head distal end surface 51a in a substantially obtuse conical
shape provided with one large and one small cutting chip discharge
ports 53A, 53B communicating with the hollow portion 52. The head
main body 51 has a head shaft center axis O which defines a
forward-to-rear axial direction of the drill head. A center cutting
blade 54A and a circumferential cutting blade 54B are formed on an
opening side edge of the large cutting chip discharge port 53A
along a head radial direction, and an intermediate cutting blade
54C is formed on an opening side edge of the small cutting chip
discharge port 53B along the same head radial direction by brazing
cutting blade tips, respectively. Further, guide pads 55A, 55B made
of cemented carbide material are brazed on an outer circumferential
surface 51b between both discharge ports 53A and 53B. On the other
hand, a drill head 50B in FIG. 10 has one cutting chip discharge
port 53 on the head distal end surface 51a and a piece of cutting
blade 54 is formed on the opening side edge along the head radial
direction by screw-clamping a throwaway tip. However, other
configurations are almost the same as those of the drill head
50A.
[0004] These drill heads 50A, 50B are such that a proximal portion
side provided with a male thread 56 on an outer circumference is
threaded into and mounted on a distal end portion of a hollow
boring bar whose illustration is omitted, and the boring bar is
coupled to a driving shaft such as a spindle of a machine tool to
be rotatingly-driven or rotate a work material side, thereby
drilling the work material by cutting blades 54A to 54C and 54 to
form a deep-hole. In addition, it is noted that a relative rotation
direction of the drill heads 50A, 50B is a counterclockwise
direction in FIG. 9(A) and FIG. 10(A). Thus, during this deep-hole
drilling work, a coolant is supplied at high pressure into a
cutting region through a gap between a cutting hole and the boring
bar, made to flow into the hollow portion 52 together with cutting
chips generated in the cutting region from the cutting chip
discharge ports 53A to 53B and 53, and discharged outside through
the inside of the hollow boring bar. In this manner, whole drilling
is carried out in these drill heads 50A, 50B, and accordingly an
inner end of a cutting blade responsible for cutting a center
portion of a cutting hole, that is, an inner end of the center
cutting blade 54A of the drill head 50A and an inner end of the
cutting blade 54 of the drill head 50B is arranged in a position
beyond a head shaft center axis O and enters into a radially
opposite side.
[0005] On the other hand, since these drill heads 50A, 50B, carry
out whole drilling so that an entire cutting hole is formed by
drilling, a cutting blade responsible for cutting the center
portion of the cutting hole, that is, the center cutting blade 54A
of the drill head 50A and the cutting blade 54 of the drill head
50B is required to be set precisely such that a blade edge 54a
matches with the radial line R passing through the head shaft
center axis O and also the inner end of the blade edge 54a is
arranged slightly beyond the head shaft center axis O. Therefore, a
cutting rate becomes zero theoretically at the head shaft center
axis O during deep-hole drilling work, and thus, a blade point
portion in the head shaft center axis O position does not exert a
cutting force at what is called a chisel edge, which results in
crushing a work material, and thrust resistance is loaded. As a
result, this has been a factor that cutting efficiency cannot be
enhanced. Further, in a configuration such as the drill head 50A
that the cutting blade tip is brazed to a recessed portion of a
head main body side, a brazing material intervenes at a fitting
portion of the both, so that high precision assembly has been
difficult.
[0006] Consequently, as for a deep-hole drilling tool employing a
screw-clamping type throwaway tip as a cutting blade, the present
inventor has already proposed one configured such that a sinking
portion is provided to a tip side surface at a cutting blade inner
end side, and the cutting blade inner end is arranged spaced apart
from the head shaft center axis O, thereby forming a non-cutting
zone in the vicinity of the shaft center and breaking off an uncut
core of a work material generated in the non-cutting zone by
press-contacting with an inclined step of the sinking portion. See
Japanese Published Unexamined Patent Application No. 2003-25129,
and Japanese Published Unexamined Patent Application No.
2003-236713.
[0007] However, when a sinking portion is provided to the cutting
blade side surface and the inner end of the cutting blade is
arranged spaced apart from the head shaft center axis O as in the
afore-proposed throwaway tip, there is a concern that the uncut
core generated in the shaft center position easily grows linearly
to a position of contacting with the inclined step, whereupon a
break-off size is enlarged and cutting chip dischargeability is
reduced. Moreover, the cutting blade itself disadvantageously
involves a great deal of trouble in processing and its
manufacturing costs become expensive due to forming of the sinking
portion on the side surface and the inclined step.
SUMMARY OF THE INVENTION
[0008] The present invention was made in view of the foregoing
circumstances, and accordingly it is an object of the present
invention to provide a drill head for deep-hole drilling in which a
cutting blade tip is mounted to face a cutting chip discharge port
opened on a head distal end surface and a hollow inside is made
into a cutting chip discharge passage communicating with the
cutting chip discharge port, wherein high cutting efficiency based
on good cutting chip dischargeability can be achieved and the
cutting blade itself is also easily processed in terms of form.
[0009] Means for achieving the aforementioned object will be
described with reference numerals of the accompanying drawings. A
drill head for deep-hole drilling D1, D2 according to a first
aspect of the present invention including one or a plurality of
cutting blade tips 2A to 2C, 3 mounted to face cutting chip
discharge ports 11 to 13 opened on a head distal end surface 1a,
and a hollow inside made into a cutting chip discharge passage 14
communicating with the cutting chip discharge ports 11 to 13. A
cutting blade tip 2A, 3 responsible for cutting the center side
("center cutting blade tip") has an inner end 20a, 30a of a blade
edge 20, 30 spaced apart from a head shaft center axis O and
forming a non-cutting zone Z in the vicinity of the shaft center O.
The cutting blade tip 2A, 3 also has, on an inner end side of the
blade edge 20, an inner side surface constituting an inclined side
surface 21, 31 inclined from the inner end of the blade edge to the
head shaft center axis O side. An uncut core C of a work material W
generated in the non-cutting zone Z is broken off by press-contact
of the inclined side surface 21, 31 of the cutting blade tip 2A, 3
during deep-hole drilling work.
[0010] A second aspect of the present invention is configured such
that the cutting blade tip 2A, 3 responsible for cutting the center
side ("center cutting blade tip") has the inclined side surface 21,
31 forming an angle of 75 to 90 degrees with respect to a tip front
surface 22, 32 in the drill head for deep-hole drilling D1, D2 of
the first aspect.
[0011] A third aspect of the present invention is configured such
that the center cutting blade tip 2A, 3 has the inner end 20a, 30a
of the blade edge 20, 30 spaced 0.05 to 0.5 mm apart from the head
shaft center axis O and also an inclination angle .theta. of the
inclined side surface 21, 31 with respect to the head shaft center
axis O is 5 to 30 degrees in the drill head for deep-hole drilling
D1, D2 of the first aspect.
[0012] A fourth aspect of the present invention is configured such
that the blade edge 20, 30 of the center cutting blade tip 2A, 3 is
arranged in parallel with a radial line R passing through the head
shaft center axis O and in a center-raised position 0.2 to 1.5 mm
more forward in a cutting rotation direction than the radial line R
in the drill head for deep-hole drilling D1, D2 of the first
aspect.
[0013] A fifth aspect of the present invention is configured such
that the cutting blade tips 2A to 2C are brazed to recessed
portions 15a to 15c provided to a head main body 1 in the drill
head for deep-hole drilling D1 of the first aspect as described
above.
[0014] A sixth aspect of the present invention is configured such
that the whole of the blade edge 20, 30 of the center cutting blade
tip 2A, 3 is inclined in a radially inward and axially forward
direction towards the head shaft center axis O side and a guide pad
6A, 7A is provided in a position on the opposite side of a mounting
side of the cutting blade tip 2A, 3 on a head outer circumferential
surface 1b in the drill head for deep-hole drilling D1, D2 of any
one of the first to the fifth aspects as described above.
[0015] Effects of the present invention will be described with
reference numerals of the drawings. First, in the drill head for
deep-hole drilling D1, D2 according to the first aspect of the
present invention, the inner end 20a, 30a of the blade edge 20, 30
of the cutting blade tip 2A, 3 is spaced apart from the head shaft
center axis O. Consequently, a non-cutting zone Z is formed in the
vicinity of the head shaft center axis O and an uncut core C of a
work material W is generated in the non-cutting zone Z during
deep-hole drilling work. However, at least the inner end side on
the inner side surface of the cutting blade tip 2A, 3 constitutes
an inclined side surface 21, 31 inclined from the inner end of the
blade edge to the head shaft center axis O side. Therefore, the
generated uncut core C is forcibly pushed away laterally by
press-contact of the inclined side surface 21, 31 and is broken off
in such a manner as being twisted in line with rotation of the
drill head D1, D2. Thus, the inclination of the inclined side
surface 21, 31 increases the degree of lateral displacement from
the head shaft center axis O as the uncut core C becomes longer. As
a result, the uncut core C is efficiently fragmented little by
little without growing long, whereupon excellent cutting chip
dischargeability is secured, and high cutting efficiency is
attained in cooperation with an elimination of the chisel edge in
the shaft center position. On the other hand, as for the cutting
blade tip 2A, 3, itself, at least the inner end side on the inner
side surface thereof has only to be a simple axially rearwardly
inclined surface, so that its manufacturing can be carried out
easily and at a low cost.
[0016] According to the second aspect of the present invention, the
inclined side surface 21, 31 of the center cutting blade tip 2A, 3
forms an angle in a specific range with respect to the tip front
surface 22, 32. Consequently, lateral displacement of the uncut
core C by press-contact of the inclined side surface 21, 31 becomes
larger, and fragmentation performance of the uncut core C is
increased accordingly, while strength of a blade point at the inner
end 20a, 30a side of the blade edge 20, 30 is increased and the
blade point resists chipping, whereupon durability of the cutting
blade tip 2A, 3 is improved.
[0017] According to the third aspect of the present invention, the
inner end 20a, 30a of the blade edge 20, 30 of the center cutting
blade tip 2A, 3 is spaced apart in a specific range from the head
shaft center axis O, and also an inclination angle .theta. of the
inclined side surface 21, 31 with respect to the head shaft center
axis O is in a specific range. Consequently, the uncut core C is
reliably broken off little by little at an appropriate
diameter.
[0018] According to the fourth aspect of the present invention, the
blade edge 20, 30 of the center cutting blade tip 2A, 3 is arranged
in an appropriate center-raised position, so that the little by
little break-off of the uncut core C is carried out more
reliably.
[0019] According to the fifth aspect of the present invention, the
cutting blade tips 2A to 2C are brazed to the recessed portions 15a
to 15c provided to the head main body 1, but the blade edge 20 of
the center cutting blade tip 2A does not need to be made in
agreement with the radial line R passing through the head shaft
center axis O. Additionally, the inner end 20a of the blade edge 20
has only to be spaced apart appropriately from the head shaft
center axis O, too. Therefore, exact positional accuracy at the
time of brazing the cutting blade tip 2A is not required, and the
manufacturing of the drill head D1 is facilitated accordingly.
[0020] According to the sixth aspect of the present invention, the
whole of the blade edge 20, 30 of the center cutting blade tip 2A,
3 is inclined in a radially inward and axially forward direction
towards the head shaft center axis O side, and also a guide pad 6A,
7A is provided in a position on the opposite side of the mounting
side of the cutting blade tip 2A, 3 on the head outer
circumferential surface 1b, so that the radial force of the cutting
reaction force is directed to the opposite side of the cutting
blade tip 2A, 3 and acts in such a manner as pressing the guide pad
6A, 7A on the opposite side of the cutting blade tip 2A, 3 against
a cutting hole H inner circumference. Thus, drilling accuracy of
the cutting hole H is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a drill head for deep-hole drilling according
to a first embodiment of the present invention, and FIG. 1(A) is a
front view and FIG. 1(B) is a side view;
[0022] FIG. 2 is a longitudinal sectional front view showing a
state of deep-hole drilling work by the drill head for deep-hole
drilling;
[0023] FIG. 3 is a longitudinal sectional side view showing a
behavior of a cutting central portion in the deep-hole drilling
work;
[0024] FIG. 4 is an explanatory diagram showing a correlation
between a center cutting blade tip and an uncut core in the
deep-hole drilling work;
[0025] FIG. 5 shows a drill head for deep-hole drilling according
to a second embodiment of the present invention, and FIG. 5(A) is a
front view and FIG. 5(B) is a side view;
[0026] FIG. 6 is a longitudinal sectional front view showing a
state of deep-hole drilling work by the drill head for deep-hole
drilling work;
[0027] FIG. 7 is a longitudinal sectional side view showing a
behavior of a cutting central portion in the deep-hole drilling
work;
[0028] FIG. 8 is an explanatory diagram showing a correlation
between a center cutting blade tip and an uncut core in the
deep-hole drilling work;
[0029] FIG. 9 shows a configuration example of a conventional drill
head for deep-hole drilling, and FIG. 9(A) is a front view and FIG.
9(B) is a side view; and
[0030] FIG. 10 shows another configuration example of the
conventional drill head for deep-hole drilling, and FIG. 10(A) is a
front view and FIG. 10(B) is a side view.
DESCRIPTION OF REFERENCE NUMERALS
[0031] 1: Head main body [0032] 1a: Distal end surface [0033] 1b:
Outer circumferential surface [0034] 11 to 13: Cutting chip
discharge port [0035] 14: Hollow portion (cutting chip discharge
passage) [0036] 15a to 15h: Recessed portion [0037] 2A: Center
cutting blade tip (cutting blade tip responsible for cutting the
center side) [0038] 20: Blade edge [0039] 20a: Inner end [0040] 21:
Inclined side surface [0041] 22: Tip front surface [0042] 3: Center
cutting blade tip (cutting blade tip responsible for cutting the
center side) [0043] 30: Blade edge [0044] 30a: Inner end [0045] 31:
Inclined side surface [0046] 32: Tip front surface [0047] 6A, 7A:
Guide pad [0048] C: Uncut core [0049] D1, D2: Drill head for
deep-hole drilling [0050] H: Cutting hole [0051] O: Head shaft
center axis [0052] R: Radial line [0053] W: Work material [0054] Z:
Non-cutting zone [0055] .theta.: Inclination angle [0056] f:
Distance (center-raised amount) [0057] s: Distance (eccentric
distance)
DETAILED DESCRIPTION
[0058] Hereinafter, embodiments of a drill head for deep-hole
drilling according to the present invention will be described in
detail with reference to the drawings. FIG. 1 shows a front and a
side of a drill head for deep-hole drilling D1 of a first
embodiment, FIG. 2 shows a state of deep-hole drilling work by the
drill head D1, FIG. 3 shows a behavior of a cutting central portion
in the deep-hole drilling work, FIG. 4 shows a correlation between
a center cutting blade tip and an uncut core in the deep-hole
drilling work, FIG. 5 shows a front and a side of a drill head for
deep-hole drilling D2 of a second embodiment, FIG. 6 shows a state
of deep-hole drilling work by the drill head D2, FIG. 7 shows a
behavior of a cutting central portion in the deep-hole drilling
work, FIG. 8 shows a correlation between a center cutting blade tip
and an uncut core in the deep-hole drilling work, respectively.
[0059] As shown in FIG. 1(A) and FIG. 1(B), the drill head for
deep-hole drilling D1 of the first embodiment has a substantially
cylindrical head main body 1 with a hollow portion 14 opened at a
proximal end side and a substantially obtuse conical-shaped head
distal end surface 1a formed with one large and one small
substantially fan-shaped cutting chip discharge ports 11, 12,
arranged opposed to each other in a radial direction and
communicating with the hollow portion 14, a center cutting blade
tip 2A and a circumferential cutting blade tip 2B on an opening
side edge of the large cutting chip discharge port 11 along a head
radial direction, and an intermediate cutting blade tip 2C on an
opening side edge of the small cutting discharge port 12 along the
same radial direction brazed to recessed portions 15a to 15c
provided to the head main body 1, respectively. The head main body
1 has a head shaft center axis O which defines a forward-to-rear
axial direction of the drill head.
[0060] Further, on a head outer circumferential surface 1b at the
distal end side of the head main body 1, recessed portions 15d, 15e
are formed on the opposite side of the mounting side of the center
cutting blade tip 2A and circumferential cutting blade tip 2B, that
is, on the mounting side of the intermediate cutting blade tip 2C
and the rear side of the center cutting blade tip 2A. Guide pads
6A, 6B of cemented carbide material are brazed to these recessed
portions 15d, 15e, and respective key ways 16 for twisting
operation are formed in radially opposed positions nearer to the
proximal end side than the mounting positions of these guide pads
6A, 6B. Further, a male thread 17 is formed on a head outer
circumferential surface 1c at the proximal end side which is
rendered smaller in outer diameter than the distal end side of the
head main body 1. This proximal end side is screwed into the distal
end portion having a female thread of the hollow boring bar whose
illustration is omitted, thereby coupling the drill head D1 to the
distal end of the boring bar.
[0061] The cutting blade tips 2A to 2C each has a blade edge 20
inclined in a radially inward and axially forward direction towards
the head shaft center axis O side and a stepped chip breaker 2a
along the blade edge 20 at the front surface side. Thus, the center
cutting blade tip 2A is arranged such that a radially inner end 20a
of the blade edge 20 is spaced apart by a distance s from the head
shaft center axis O in a position where the blade edge 20 is
parallel to the radial line R passing through the head shaft center
axis O and also a center thereof is raised by a distance f more
forward in the cutting rotation direction than the radial line R.
Further, the inner side surface of the center cutting blade tip 2A
constitutes an inclined side surface 21 in which the whole is
axially rearwardly inclined from the inner end side to the head
shaft center axis O side, and the surface orientation is set at a
right angle to the tip front surface 22. On the other hand, the
circumferential cutting blade tip 2B and the intermediate cutting
blade tip 2C are both arranged in such a manner that respective
blade edges 20 match with the radial line R passing through the
head shaft center axis O.
[0062] In deep-hole drilling work by the above-described drill head
for deep-hole drilling D1, the coolant supplied through a gap
between an inner circumference of a cutting hole H and an outer
circumference of the hollow boring bar and drill head D1 is sent
into a cutting region continuously while the drill head D1 coupled
to the boring bar as already described above or a work material W
is rotated, cutting chips generated in the cutting region are
caught in the coolant, passed through the hollow portion 14 and a
hollow inside of the boring bar from the cutting chip discharge
ports 11, 12 of the drill head D1, and discharged outside.
[0063] As described above, the inner end 20a of the blade edge 20
of the center cutting blade tip 2A is spaced apart from the head
shaft center axis O in this drill head for deep-hole drilling D1,
whereby a circular non-cutting zone Z whose radius is an eccentric
distance s is formed in the vicinity of the shaft center O, as
shown in FIG. 2 and FIG. 3, and an uncut core C of a work material
W is generated in this non-cutting zone Z. Therefore, since the
inner side surface of the cutting blade tip 2A constitutes an
inclined side surface 21 axially rearwardly inclined from the inner
end side to the head shaft center axis O side, as shown in FIG. 3,
the uncut core C does not grow along the head shaft center axis O
as shown by a virtual line, but is forcibly pushed away laterally
by press-contact of the axially rearwardly inclined side surface 21
as shown by a solid line, and is broken off in such a manner as
being twisted in line with rotation of the drill head. Thus, the
axially rearward inclination of the inclined side surface 21
increases the degree of lateral displacement from the head shaft
center axis O as the uncut core C becomes longer. Therefore, the
uncut core C is efficiently fragmented little by little without
growing long, whereupon excellent cutting chip dischargeability is
secured, and high cutting efficiency is attained in cooperation
with an elimination of the chisel edge in the shaft center
position.
[0064] Furthermore, in this embodiment, the blade edge 20 of the
center cutting blade tip 2A is arranged in a center-raised position
by a distance f more forward than the radial line R passing through
the head shaft center axis O, and the inclined side surface 21 at
the inner end side is perpendicular to the tip front surface 22.
Consequently, as shown in FIG. 4, a side surface continuing from
the inner end 20a of the blade edge 20 to the rearward, that is, an
upper end edge 21a on the inclined side surface 21 comes to enter
into the non-cutting zone Z by the shaded portion U as shown since
the shortest distance d with respect to the head shaft center axis
O becomes shorter than the eccentric distance s of the inner end
20a of the blade edge 20. Therefore, the uncut core C generated by
the cutting by the blade edge 20 is pushed and cut from the side by
as much as the shaded portion U just after the generation, and is
constricted to a circle N having a smaller radius d than the
non-cutting zone Z. As a result, the uncut core C is easily broken
off further little by little.
[0065] It is noted that the inner end 20a of the blade edge 20 of
the center cutting blade tip 2A is shown as an acute angle for easy
understanding of the description in FIG. 4, but is actually
round-shaped as shown in FIG. 3 in order to resist chipping,
whereby the upper end edge 21a on the inclined side surface 21
continuing to the inner end 20a also constitutes a round shape
throughout its length. And, even with such a round shape, it is the
same that the uncut core C is pushed and cut from the side by as
much as the shaded portion U just after the generation.
[0066] Further, in this embodiment, the whole of the blade edge 20
of the center cutting blade tip 2A is inclined in a radially inward
and axially forward direction towards the head shaft center axis O
side, so that the radial force of the cutting reaction force is
directed to the opposite side of the cutting blade tip 2A side and
acts in such a manner as pressing the guide pad 6A on the opposite
side of the cutting blade tip 2A against a cutting hole H inner
circumference. Thus, there is also an advantage of improving
drilling accuracy of the cutting hole H. In contrast, the radial
force is directed to the outer circumferential cutting blade 54B
side when the blade edge of the center cutting blade 54A is
inclined on both sides of the head shaft center axis O as in the
conventional configuration of FIG. 9(A) and FIG. 9(B). As a result,
the cutting hole H tends to be enlarged, which is subject to a
reduction in drilling accuracy.
[0067] In the drill head D1 of this embodiment, on the other hand,
the cutting blade is composed of the cutting blade tips 2A to 2C
brazed to the recessed portions 15a to 15c provided to the head
main body 1, but the blade edge 20 of the center cutting blade tip
2A does not need to be made in agreement with the radial line R
passing through the head shaft center axis O. Additionally, the
inner end 20a of the blade edge 20 also has only to be spaced apart
from the head shaft center axis O appropriately, so that exact
positional accuracy is not required at the time of brazing the
center cutting blade tip 2A, which facilitates the manufacturing of
the drill head D1 accordingly. Further, as for the center cutting
blade tip 2A itself as well, the inner side surface thereof has
only to be a simple inclined side surface 21, so that its
manufacturing can be carried out easily and at a low cost.
[0068] A drill head for deep-hole drilling D2 of a second
embodiment has, as shown in FIG. 5(A) and FIG. 5(B), a
substantially cylindrical head main body 1 with a hollow portion 14
opened at a proximal end side and a substantially obtuse
conical-shaped head distal end surface 1a formed with a
substantially fan-shaped cutting chip discharge port 13
communicating with the hollow portion 14, and a cutting blade tip 3
composed of a throwaway tip is screw-clamped on an opening side
edge along the head radial direction. Additionally, on a head outer
circumferential surface 1b at the distal end side of the head main
body 1, recessed portions 15h, 15g are formed on the opposite side
of the mounting side of the cutting blade tip 3 and the rear side
of the cutting blade tip 3 in the same manner as the
afore-described first embodiment. Guide pads 7A, 7B of cemented
carbide material are brazed to these recessed portions 15h, 15g,
and also respective flat portions 18 for twisting operation are
formed in radially opposed positions nearer to the proximal end
side than the mounting positions of these guide pads 7A, 7B.
Further, a male thread 19 is formed on the head outer
circumferential surface 1c at the proximal end side which is
rendered smaller in outer diameter.
[0069] The cutting blade tip 3 has a blade edge 30 forming a
three-step shape and inclined in a radially inward and axially
forward direction towards the head shaft center axis O side. The
cutting blade tip 3 has a stepped chip breaker 3a at the front
surface side along an inclination direction of the blade edge 30.
The cutting blade tip 3 is arranged such that a radially inner end
30a of the blade edge 30 is spaced apart by a distance s from the
head shaft center axis O in a position where the blade edge 30 is
parallel to the radial line R passing through the head shaft center
axis O and also a center thereof is raised by a distance f more
forward in the cutting rotation direction than the radial line R.
Further, a portion at an inner end side of the inner side surface
of the cutting blade tip 3 constitutes an inclined side surface 31
axially rearwardly inclined from the inner end side to the head
shaft center axis O side, and the surface orientation is set at a
right angle to the tip front surface 32.
[0070] In deep-hole drilling work by the above-described drill head
for deep-hole drilling D2, the drill head D2 is coupled to the
distal end of the boring bar by the male thread 19 in the same
manner as the afore-described first embodiment, the coolant
supplied through a gap between an inner circumference of a cutting
hole H and an outer circumference of the hollow boring bar and
drill head D2 is sent into a cutting region continuously while the
drill head D2 or a work material W is rotated, cutting chips are
caught in the coolant, passed through the hollow portion 14 and a
hollow inside of the boring bar from the cutting chip discharge
port 13 of the drill head D2, and discharged outside.
[0071] In the same manner as the afore-described first embodiment,
the inner end 30a of the blade edge 30 of the cutting blade tip 3
is spaced apart from the head shaft center axis O in this drill
head for deep-hole drilling D2 of the second embodiment as well,
whereby a circular non-cutting zone Z whose radius is an eccentric
distance s is formed in the vicinity of the shaft center O, as
shown in FIG. 6 and FIG. 7, and an uncut core C of a work material
W is generated in this non-cutting zone Z. Therefore, since the
inner end side on the inner side surface of the cutting blade tip 3
constitutes the afore-mentioned inclined side surface 31, as shown
in FIG. 7, the uncut core C does not grow along the head shaft
center axis O as shown by a virtual line, either, but is forcibly
pushed away laterally by press-contact of the inclined side surface
31 as shown by a solid line, and is broken off in such a manner as
being twisted in line with rotation of the drill head. Then, the
uncut core C increases the degree of lateral displacement from the
head shaft center axis O as it becomes longer. Therefore, the uncut
core C is efficiently fragmented little by little without growing
long, whereupon excellent cutting chip dischargeability is secured,
and high cutting efficiency is attained in cooperation with an
elimination of the chisel edge in the shaft center position.
[0072] Furthermore, in this embodiment as well, the blade edge 30
of the cutting blade tip 3 is arranged in a center-raised position
by a distance f more than the radial line R passing through the
head shaft center axis O, and the inclined side surface 31 at the
inner end side is perpendicular to the tip front surface 32.
Consequently, as shown in FIG. 8, a side surface continuing from
the inner end 30a of the blade edge 30 to the rearward, that is, an
upper end edge 31a on the inclined side surface 31 comes to enter
into the non-cutting zone Z by the shaded portion U as shown since
the shortest distance d with respect to the head shaft center axis
O becomes shorter than the eccentric distance s of the inner end
30a of the blade edge 30. Therefore, the uncut core C generated by
the cutting by the blade edge 30 is pushed and cut from the side by
as much as the shaded portion U just after the generation, and is
constricted to a circle N having a smaller radius d than the
non-cutting zone Z. As a result, the uncut core C is easily broken
off further little by little. Further, the whole of the blade edge
30 of the cutting blade tip 3 is inclined in a radially inward and
axially forward direction towards the head shaft center axis O
side, so that the radial force of the cutting reaction force is
directed to the opposite side of the cutting blade tip 3 side and
acts in such a manner as pressing the guide pad 7A on the opposite
side of the cutting blade tip 3 against a cutting hole H inner
circumference. Thus, drilling accuracy of the cutting hole H is
improved.
[0073] An inclination angle .theta. of the inclined side surface
21, 31 at the inner end side of the center cutting blade tip 2A, 3
with respect to the head shaft center axis O is preferably in the
range of 5 to 30 degrees in the drill head for deep-hole drilling
of the present invention. If the inclination angle .theta. is too
small or too large, break-off performance (fragmentation
performance) of the uncut core C becomes low. Further, the
eccentric distance s of the inner end 20a, 30a of the blade edge
20, 30 of the center cutting blade tip from the head shaft center
axis O is preferably in the range of 0.05 to 0.5 mm. If too short,
positioning of the cutting blade tip becomes difficult, whereas if
too long, the uncut core C becomes thick, which requires a large
force for break-off and leads to a reduction in cutting efficiency.
Furthermore, a center-raised amount of the center cutting blade tip
2A, 3, in other words, a distance f of the blade edge 20, 30 with
respect to the radial line R passing through the head shaft center
axis O is preferably in the range of 0.2 to 1.5 mm for the purpose
of further ensuring the little by little break-off of the uncut
core C.
[0074] It is noted that the inclined side surface at the inner end
side of the center cutting blade tip is perpendicular to the tip
front surface in the afore-described embodiments. However, the
inclined side surface has only to be in the angle range of 75 to 90
degrees with respect to the tip front surface in the present
invention. In this angle range, the lateral displacement of the
uncut core C by press-contact of the inclined side surface becomes
sufficiently large and fragmentation performance of the uncut core
is increased accordingly, while strength of a blade point at the
inner end side of the blade edge of the cutting blade tip is
increased, so that the blade point resists chipping, whereupon
durability of the cutting blade is improved. Moreover, detailed
configurations such as the shape of the cutting blade tip, the
shape of the guide pad, etc., can be modified in various ways
except for the embodiments in the present invention.
* * * * *