U.S. patent number RE44,915 [Application Number 12/640,882] was granted by the patent office on 2014-05-27 for modular drill.
This patent grant is currently assigned to Kennametal Inc.. The grantee listed for this patent is Filho Ruy Frota de Souza. Invention is credited to Filho Ruy Frota de Souza.
United States Patent |
RE44,915 |
de Souza |
May 27, 2014 |
Modular drill
Abstract
A drill having a replaceable cutting head, modified to eliminate
forces which would distort the pocket of the drill shank and
otherwise concentrate stresses which would cause failure of the
drill. The cutting head has a frustoconical depending connecting
member received in a receptacle formed in the shank. In different
embodiments, contact between the pocket formed in the shank and the
cutting head connecting member is limited. In one embodiment, angle
of drive surfaces is modified from prior art practice. In another
embodiment, transition of at curved joints between vertical and
horizontal surfaces is made more gradual. The drill preferably has
flutes formed collectively by the shank and cutting head when
assembled.
Inventors: |
de Souza; Filho Ruy Frota
(Latrobe, PA) |
Applicant: |
Name |
City |
State |
Country |
Type |
de Souza; Filho Ruy Frota |
Latrobe |
PA |
US |
|
|
Assignee: |
Kennametal Inc. (Latrobe,
PA)
|
Family
ID: |
36125713 |
Appl.
No.: |
12/640,882 |
Filed: |
December 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10958227 |
Oct 5, 2004 |
7309196 |
Dec 18, 2007 |
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Current U.S.
Class: |
408/227;
408/231 |
Current CPC
Class: |
B23B
51/00 (20130101); Y10T 408/909 (20150115); Y10T
408/9098 (20150115); B23B 2251/02 (20130101); Y10T
408/9097 (20150115) |
Current International
Class: |
B23B
51/02 (20060101); B23B 51/12 (20060101) |
Field of
Search: |
;408/227,144,231,233,226,713 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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94 340 |
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Sep 1896 |
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DE |
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524 677 |
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Apr 1931 |
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DE |
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2 246 965 |
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Apr 1974 |
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DE |
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199 45 097 |
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Mar 2001 |
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DE |
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100 54 850 |
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May 2002 |
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DE |
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0 118 806 |
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Sep 1984 |
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EP |
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0 441 302 |
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Aug 1991 |
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EP |
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0 441 302 |
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Aug 1991 |
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EP |
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0 460 237 |
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Dec 1991 |
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EP |
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907 980 |
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May 1944 |
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FR |
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1 395 855 |
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May 1975 |
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GB |
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2 010 708 |
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Jul 1979 |
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GB |
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Primary Examiner: Fridie, Jr.; Will
Attorney, Agent or Firm: Meenan, Esq.; Larry R.
Claims
What is claimed is:
1. A cutting tool assembly for conducting rotary cutting operations
on a work piece, .Iadd.said cutting tool assembly
.Iaddend.comprising a tool shank and a replaceable cutting head
which is installed on and engages the tool shank, the tool shank
and the cutting head having a common rotational axis and mating
peripheral surfaces when assembled together, the cutting tool
assembly having a leading end which engages the work piece and a
trailing end located oppositely from the leading end, relative to
the rotational axis; the shank having a pocket for coupling to the
cutting head, an interlocking member arranged to retain the cutting
head when the cutting head is installed within the pocket, at least
one abutment surface abutting the cutting head when the cutting
head is installed within the pocket, and at least one driving
surface arranged to rotate the cutting head when the shank is
rotated with the cutting head installed within the pocket; the
cutting head having a cutting portion at the leading end of the
cutting tool assembly, an interlocking member engaging the
interlocking member of the shank, and a driven surface oriented to
abut the driving surface of the shank when the cutting head is
installed within the pocket; wherein the interlocking member of the
cutting head comprises a lateral surface oriented at an obtuse
angle to the rotational axis and facing the cutting portion of the
cutting head, and an extension adjacent to the lateral surface and
projecting away from the cutting portion of the cutting head,
.Iadd.wherein the pocket of the shank has a floor portion and a
surface that corresponds to the lateral surface of the cutting
head, .Iaddend.whereby the extension reinforces the interlocking
member at the lateral surface oriented at an obtuse angle to the
rotational axis such that stresses are minimized due to a
.[.smoother.]. .Iadd.smooth .Iaddend.transition between the
.[.dovetail.]. .Iadd.surface of the pocket corresponding to the
lateral surface of the cutting tool .Iaddend.and the .[.pocket.].
floor .Iadd.portion of the pocket.Iaddend..
2. The cutting tool assembly according to claim 1, wherein the
extension projecting away from the cutting portion of the cutting
head has a cylindrical outer surface.
3. The cutting tool assembly according to claim 1, wherein the
extension projecting away from the cutting portion of the cutting
head has a tapered outer surface.
4. The cutting tool assembly according to claim 1, wherein the
pocket has at least one internally facing surface oriented to abut
the lateral surface .[.of the dovetail member.]. of the cutting
head, the internally facing surface being dimensioned and
configured to abut the .[.dovetail member.]. .Iadd.lateral surface
.Iaddend.of the cutting head along part of the extent of the
lateral surface .[.of the dovetail member.]. and to avoid making
contact along the balance of the lateral surface .[.of the dovetail
member.]., whereby the uncontacted portion of the pocket allows for
deflection of the pocket walls when forces are imposed on the
pocket by the cutting head during cutting operations of the cutting
tool, thereby mitigating radial deflection of the pocket walls.
5. The cutting tool assembly according to claim 1, wherein the
driving surface of the shank is disposed out of radial orientation
with respect to the rotational axis such that the driving surface
has a leading inner portion and a trailing outer portion, whereby
resistive forces imposed by the cutting head during cutting
operations acting perpendicularly against the driving surface have
an inward component tending to compress the wall of the pocket
inwardly during cutting operations, thereby opposing forces imposed
.Iadd.by .Iaddend.the cutting head which would otherwise tend to
spread open the pocket.
6. The cutting tool assembly according to claim 1, further
comprising a circumferential surface and two opposed flutes each
projecting into the tool shank along the circumferential surface,
wherein the pocket further comprises a first pocket wall and a
diametrically opposed second pocket wall spaced apart from the
first pocket wall and the pocket has a floor which separates and
spaces apart the first pocket wall from the second pocket wall and
which bears a relief trough projecting into the shank towards the
trailing end of the cutting tool assembly and extending across and
spanning the floor from one flute to the other flute, a first shelf
extending laterally across the floor at an upper edge of the relief
trough at the first pocket wall and a second shelf extending
laterally across the floor at another upper edge of the relief
trough at the second pocket wall, and the relief trough is
angularly oriented relative to the rotational axis such that the
first shelf intersects only one flute and the trough is disposed
between the first shelf and the other flute, and the second shelf
intersects only one flute and the trough is disposed between the
second shelf and the other flute.
.Iadd.7. A cutting tool assembly for conducting rotary cutting
operations on a work piece, the cutting tool assembly comprising: a
tool shank and a replaceable cutting head which is installed on and
engages the tool shank, the tool shank and the cutting head having
a common rotational axis and mating peripheral surfaces when
assembled together, the cutting tool assembly having a leading end
which engages the work piece and a trailing end located oppositely
from the leading end, relative to the rotational axis; the cutting
head having: a cutting portion at the leading end of the cutting
tool assembly; a driven surface; and an interlocking member
comprising: a lateral surface oriented at an obtuse angle to the
rotational axis and facing the cutting portion of the cutting head;
and an extension adjacent to the lateral surface and projecting
away from the cutting portion of the cutting head; and the shank
having: a pocket including a pocket floor and an internally facing
surface oriented to abut the lateral surface of the cutting head,
the pocket being arranged to engage the interlocking member of the
cutting head and retain the cutting head when the cutting head is
installed within the pocket; at least one abutment surface abutting
the cutting head when the cutting head is installed within the
pocket; and at least one driving surface oriented to abut the
driven surface of the cutting head and arranged to rotate the
cutting head when the shank is rotated with the cutting head
installed within the pocket. .Iaddend.
.Iadd.8. The cutting tool assembly according to claim 7, wherein
the extension adjacent to the lateral surface and projecting away
from the cutting portion of the cutting head has a cylindrical
outer surface. .Iaddend.
.Iadd.9. The cutting tool assembly according to claim 7, wherein
the extension adjacent to the lateral surface and projecting away
from the cutting portion of the cutting head has a tapered outer
surface. .Iaddend.
.Iadd.10. The cutting tool assembly according to claim 7, wherein
the pocket has at least one internally facing surface oriented to
abut the lateral surface of the cutting head, the internally facing
surface being dimensioned and configured to abut the lateral
surface along part of the extent of the lateral surface and to
avoid making contact along the balance of the lateral surface,
whereby the uncontacted portion of the pocket allows for deflection
of the pocket walls when forces are imposed on the pocket by the
cutting head during cutting operations of the cutting tool, thereby
mitigating radial deflection of the pocket walls. .Iaddend.
.Iadd.11. The cutting tool assembly according to claim 7, wherein
the driving surface of the shank is disposed out of radial
orientation with respect to the rotational axis such that the
driving surface has a leading inner portion and a trailing outer
portion, whereby resistive forces imposed by the cutting head
during cutting operations acting perpendicularly against the
driving surface have an inward component tending to compress the
wall of the pocket inwardly during cutting operations, thereby
opposing forces imposed the cutting head which would otherwise tend
to spread open the pocket. .Iaddend.
.Iadd.12. The cutting tool assembly according to claim 7, further
comprising a circumferential surface and two opposed flutes each
projecting into the tool shank along the circumferential surface,
wherein the pocket further comprises a first pocket wall and a
diametrically opposed second pocket wall spaced apart from the
first pocket wall and the pocket has a floor which separates and
spaces apart the first pocket wall from the second pocket wall and
which bears a relief trough projecting into the shank towards the
trailing end of the cutting tool assembly and extending across and
spanning the floor from one flute to the other flute, a first shelf
extending laterally across the floor at an upper edge of the relief
trough at the first pocket wall and a second shelf extending
laterally across the floor at another upper edge of the relief
trough at the second pocket wall, and the relief trough is
angularly oriented relative to the rotational axis such that the
first shelf intersects only one flute and the trough is disposed
between the first shelf and the other flute, and the second shelf
intersects only one flute and the trough is disposed between the
second shelf and the other flute. .Iaddend.
.Iadd.13. A replaceable cutting head for use with a shank for
conducting rotary cutting operations on a work piece, the shank
having a rotational axis, a driving surface, and a pocket having an
internally facing surface, the replaceable cutting head comprising:
a rotational axis; a cutting portion; a driven surface structured
to abut the drive surface of the shank and be rotated when the
shank is rotated with the cutting head installed; and an
interlocking member structured to engage the pocket of the tool
shank in a manner that retains at least a portion of the cutting
head within the pocket, the interlocking member comprising: a
lateral surface oriented at an obtuse angle to the rotational axis
of the cutting head and facing the cutting portion of the cutting
head; and an extension adjacent to the lateral surface and
projecting away from the cutting portion of the cutting head.
.Iaddend.
.Iadd.14. The replaceable cutting head according to claim 13,
wherein the extension adjacent to the lateral surface and
projecting away from the cutting portion of the cutting head has a
cylindrical outer surface. .Iaddend.
.Iadd.15. The replaceable cutting head according to claim 13,
wherein the extension adjacent to the lateral surface and
projecting away from the cutting portion of the cutting head has a
tapered outer surface. .Iaddend.
.Iadd.16. The replaceable cutting head according to claim 13,
wherein the driving surface of the shank is disposed out of radial
orientation with respect to the rotational axis such that the
driving surface has a leading inner portion and a trailing outer
portion, whereby resistive forces imposed by the cutting head
during cutting operations acting perpendicularly against the
driving surface have an inward component structured to generally
compress the wall of the pocket inwardly during cutting operations,
thereby opposing forces imposed by the cutting head which would
otherwise tend to spread open the pocket. .Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to cutting tools, and more
particularly to modular drills having replaceable cutting tips.
DESCRIPTION OF THE RELATED ART
Drills having replaceable cutting tips are known. Illustratively,
such tools are shown in U.S. Pat. Nos. 5,957,631 and 6,059,492,
both issued to Gil Hecht on Sep. 28, 1999, and May 9, 2000,
respectively. The subject drills have replaceable cutting heads
which are mounted on shanks. The cutting heads and shanks display
continuous and complementing configuration as fluted drills. To
this end, each shank has structure for retaining and rotating an
associated cutting head. The associated cutting head has
complementing structure for being retained and rotated by the
shank. While these devices will operate under some circumstances,
closer analysis reveals that their useful lives are potentially
unduly limited. More specifically, the retaining and drive
structure of the shank is subject to deformation and failure during
its service life due to concentration of stresses imposed during
ordinary service.
SUMMARY OF THE INVENTION
The present invention provides modifications to drills having
replaceable cutting tips, of the type shown in the above referenced
patents to Hecht. The modifications of the present invention alter
stresses imposed on the shanks such that the shanks either do not
undergo deformation and outright failure while in service or
alternatively, increase the service life achievable before
deformation renders the tool unusable. These modifications
generally connote prevention of direct contact of a replaceable
cutting head with the shank at certain specified locations. Also,
orientations of certain abutting surfaces are modified so that
stresses are imposed differently from the original design of
Hecht.
One specific example of modifications is that of providing a gap
between a frustoconical dovetail formed in the cutting head and a
cooperating recess formed in the shank, at the forward and rearward
areas of mutual contact. The area of contact is limited to that
portion between the forward and rearward areas of contact. A second
modification is that of altering the angle of drive or torque
transmission surfaces from purely radial to inclined relative to a
purely radial direction. This has the effect of redistributing
forces which would otherwise act on the walls of a pocket formed in
the shank. The pocket, which receives the connection structure of
the cutting head, then better resists distorting forces. A third
modification is that of lengthening at the walls of that portion of
the body forming a pocket which receives the cutting head and
eliminating sharp corners in this region of the body. In still
another modification, the floor of the pocket is modified in the
manner of the third modification.
These modifications redistribute distorting forces away from
portions of the shank which are more susceptible to distortion to
portions of the shank better able to withstand these forces. The
ultimate effect is to increase the useful service life of the shank
due to reduced distortion of the pocket.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features of the present invention, as well as the
advantages derived therefrom, will become clear from the following
detailed description made with reference to the drawings in
which:
FIG. 1 is a partial, exploded perspective view of one embodiment of
the modular drill of the present invention.
FIG. 2 is an end elevational detail view of the lower end of the
upper component of FIG. 1, but showing an alternative embodiment
thereof.
FIG. 3 is a cross sectional view of a further embodiment of the
invention. The cross section corresponds to that which could be
taken through the components of FIG. 1 if the components of FIG. 1
were assembled in axial abutment.
FIG. 4A is a cross sectional view of a still further embodiment of
the invention, corresponding to FIG. 3 but with structure modified
therefrom.
FIG. 4B is a cross sectional view of still another embodiment of
the invention, corresponding to FIG. 4A, but with structure
modified therefrom.
FIG. 5 is a top plan view of an alternative embodiment of the lower
component of FIG. 1.
FIG. 6 is a partial, exploded view of another embodiment of the
invention.
FIG. 7 is a perspective detail view of a further embodiment of the
upper component of FIG. 1.
FIG. 8 is a partial, side elevational view of a still further
embodiment of the invention.
FIG. 9 is an enlarged perspective detail view of the embodiment of
FIG. 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The documents, patents and patent applications referred to herein,
including those pertaining to the prior art, are hereby
incorporated by reference in their entirety. FIG. 1 of the drawings
shows a first embodiment of a cutting tool assembly 10 for
conducting rotary cutting operations on a work piece (not shown),
comprising a tool shank 12 and a replaceable cutting head 14 which
is installed on and engages tool shank 12. Cutting tool assembly 10
is a modular drill which in the preferred embodiments is of the
so-called twist drill type, having helical flutes disposed along
the sides of the drill. In the embodiment of FIG. 1, two flutes are
provided in diametric opposition to one another, only one flute
being visible. The visible flute has a lateral recess forming part
of a flute, or cutting head flute portion 16 formed in cutting head
14. A corresponding or complementing lateral recess or shank flute
portion 18 is formed in shank 12. The depiction of FIG. 1 shows
cutting head 14 in a position for initially being installed on
shank 12. In this initial position, cutting head 14 is rotated
about ninety degrees with respect to rotational axis 20 of cutting
tool 10, which rotational axis 20 is common to both shank 12 and
also cutting head 14. Installation of cutting head 14 requires that
cutting head 14 be lowered into abutment or near abutment with
shank 12 and rotated in a direction opposite that of rotation
during cutting operations. This installation procedure will both
interlock cutting head 14 with shank 12 at certain respective
mating peripheral surfaces in a manner precluding disengagement in
the axial direction, taken with respect to axis 20, and will also
assure abutment of driving surfaces 22, 24 of shank 12 with
corresponding driven surfaces 26, 28 of cutting head 14. Driving
surfaces 22, 24 of shank 12 are oriented to abut and bear against
driven surfaces 26, 28 of cutting head 14 and thereby rotate
cutting head 14 in tandem with shank 12 when shank 12 is rotated by
its associated cutting tool such as a hand drill, drill press,
machine tool, or the like (none shown).
Once cutting head 14 is installed on shank 12, the flute
collectively formed by cutting head flute portion 16 and shank
flute portion 18 will align to form a flute in generally continuous
and undistorted fashion. A similar flute is of course formed on the
other side of cutting tool 10. Although two flutes are preferred,
any number of flutes including only one is possible.
In the depiction of FIG. 1, cutting head flute portion 16 emerges
at a leading end 30 of cutting tool 10. Leading end 30 is defined
for semantic purposes, and is that end which engages a work piece
(not shown) when cutting. During cutting operations, cutting tool
10 is mounted in the rotary cutting tool, rotated, and advanced
progressively into the work piece as cutting progresses. That end
of cutting tool located oppositely leading end 30 is termed the
trailing end 32. The terms "leading end 30" and "trailing end 32"
are semantic devices which apply equally to shank 12 and cutting
head 14 as they connote directional orientation with respect to
longitudinal and rotational axis 20 rather than specific structure.
Leading end 30 is that which penetrates a work piece (not shown),
and trailing end 32 is that end opposed to leading end 30.
That portion of shank 12 which couples to and rotates cutting head
14 is referred to as pocket 34. The principal elements of pocket 34
include two generally symmetrical and similar castellated wall
sections 36, 38. Wall section 36 will be described, it being
understood that wall 38 is a generally symmetrical counterpart
thereof. Wall section 36 is essentially a continuation of the body
of shank 12 which projects upwardly in the depiction of FIG. 1 past
a central floor portion 40 of shank 12, along the outer periphery
of shank 12. Wall section 36 has a smooth outer surface 42 which
conforms to and is generally coextensive with the generally
cylindrical outer surface of cutting tool 10. At the interior of
wall section 36, the term "interior" referring to those surfaces
facing axis 20, wall section 36 has an internally facing, generally
cylindrical face 44 and a frustoconical face 46. Wall section 36
also has an upwardly facing upper face 48, an upwardly facing lower
face 50, and a lateral face 52. Lateral face 52 is located on a
side opposite that of driving surface 22.
Cutting head 14 has cutting edges (only cutting edge 54 is visible
in FIG. 1), a peripheral generally cylindrical outer surface 56,
and a leading conical surface 58 which conical surface 58 is of
course interrupted or incomplete due to presence of the flutes.
Cutting edge 54 and leading conical surface 58 collectively form a
cutting portion which performs cutting operations to the work
piece.
Any or all of central floor portion 40, faces 48 and 50, and faces
formed in wall portion 38 corresponding to faces 48 and 50 serve as
abutment surfaces which abut cutting head 14 when cutting head 14
is installed on shank 12.
Cutting head 14 has a shank connection portion opposite the cutting
portion, or alternatively stated, facing the trailing end of
cutting head 14, in the form of an interlocking member arranged to
retain cutting head 14 within pocket 34 of shank 12. In the
embodiment of FIG. 1, this interlocking member comprises a dovetail
member 60 which is located centrally along rotational axis 20.
Dovetail member 60 is so-called due to its characteristic
frustoconical lateral surface 62 which surface 62 is arranged at an
obtuse angle to rotational axis 20. Dovetail member 60 provides an
interlocking member corresponding to and engaging pocket 34, which
pocket 34 serves as an interlocking member of shank 12. Surrounding
dovetail member 60 is a peripheral base surface facing pocket 34,
comprising cutting head faces 64, 66, 68, which face downwardly in
the depiction of FIG. 1. It should be understood at this point that
cutting head 14 is generally bilaterally symmetrical, so that
cutting head face 64 is generally a mirror image of cutting head
face 68. Similarly, there exists a cutting head face not visible in
FIG. 1 and not identified by reference numeral, which is
diametrically opposed to and generally rotationally symmetrical
about the central axis. In those embodiments wherein there may be
three flutes, for example, there will accordingly be three rather
than two similar cutting head faces corresponding to cutting heads
64, 66 disposed about the periphery of the cutting head.
Faces 64, 66 may be stepped, or located at different levels or
points along axis 20, in the same manner as and to correspond to
the axial spacing apart of faces 48 and 50 of shank 12. Any or all
of faces 64, 66 serve as abutment surfaces for abutting shank 12.
Abutment of faces 64, 66 with their corresponding surfaces 48, 50
of shank 12 seats cutting head 14 on shank 12 responsive to
compressive axial loading. When rotated into the interlocked
position with respect to pocket 34, dovetail member 60 will engage
interior frustoconical face 46 of pocket 34, thereby preventing
disengagement in the axial direction away from shank 12.
It is an important feature of the invention that contact between
frustoconical face 46 and frustoconical lateral surface 62 be
limited such that contact not occur over the entire extent of face
46 or lateral surface 62. Rather, frustoconical face 46 and
frustoconical lateral surface 62 are dimensioned and configured to
abut mutually along part of the extent of surface 62 and to avoid
making contact along the balance of lateral surface 62. This
characteristic enables pocket 34 to experience minimized forces
imposed thereon during cutting operations by cutting head 14, which
forces would otherwise tend to spread or distort pocket 34.
Alternatively stated, although tangential forces remain unchanged,
forces imposing a radially outward component are minimized at
critical areas. Pocket 34 is thus less subject to distorting forces
which would otherwise cause pocket 34 to spread over time of use,
thereby shortening the useful life of shank 12. Representative
areas 70, 72 of non-contact between face 46 and surface 62 are
shown stippled in FIG. 1.
Non-contact of face 46 and surface 62 may be accomplished in
several ways. Turning now to FIG. 2, dovetail member 60 is seen in
bottom plan. The periphery of dovetail member 60 includes reliefs
74, 76 to allow for chip flow after installation, arcuate sections
78, 80, and chamfers 82, 84, 86, 88. Chamfers 82, 84, 86, 88 reduce
the overall diameter of trailing surface 90 of dovetail member 60.
The resulting discrepancy between the full diameter and that at any
of chamfer 82, 84, 86, or 88 is indicated by arrowheads as gaps 92,
94, 96, 98 which exist between respective chamfers 82, 84, 86, 88
and extensions (shown in broken lines) of the arcuate configuration
of the periphery of surface 90. In the embodiment of FIG. 2, then,
contact between dovetail member 60 and face 46 of pocket 34 is made
along arcuate sections 78 and 80, but is avoided at chamfers 82,
84, 86, 88, where the diameter of dovetail member 60 is reduced.
The pocket of the shank (neither shown) which corresponds to
dovetail member 60 thus contacts only first and second arcuate
portions 78, 80 of dovetail member 60, and avoids contacting
chamfered portions 82, 84, 86, 88.
Referring now to FIG. 3, which is an end view of a dovetail member
100 of a cutting head (not shown in its entirety) installed in a
pocket (not shown in its entirety) of a shank, a similar effect is
obtained by chamfering walls 102, 104 of the pocket. The cutting
head associated with dovetail member 100 may be essentially similar
to cutting head 14 of FIG. 1. The shank of FIG. 3, apart from
chamfering discussed herein, is essentially similar to shank 12 of
FIG. 1, similarity extending to the pocket. In the embodiment of
FIG. 3, chamfered portions 106, 108, 110, 112 formed in internally
facing surfaces of pocket walls 102, 104 create gaps 114, 116, 118,
120 which provide functions similar to those of gaps 92, 94, 96, 98
of the embodiment of FIG. 2. Gaps 114, 116, 118, 120 separate the
arcuate sections (not specifically called out by reference numeral)
of pocket walls 102, 104 from dovetail member 100 at the ends of
pocket walls 102, 104. Thus the internally facing surfaces of
pocket walls 102, 104 contact dovetail member 100 only at their
respective arcuate sections and avoid making contact at chamfered
portions 106, 108, 110, 112. The difference between the embodiments
of FIGS. 2 and 3 is that in the embodiment of FIG. 2, dovetail
member 90 receives chamfering, whereas in the embodiment of FIG. 3,
walls 102, 104 of the pocket of the shank receive chamfering.
The dovetail member is limited to an extent less than the full
extent of the internally facing surfaces of the pocket when the
cutting head is installed in the pocket. More particularly, it is
presently preferred that the zone of contact extend along the
interior of each of walls 124A and 126A within a range of about
fifteen to about seventy-five degrees.
FIG. 4A shows an embodiment of the invention utilizing a third way
of limiting contact between a dovetail member 122A of a cutting
head (not shown in its entirety) and the pocket of a shank (not
shown in its entirety). In FIG. 4A, walls 124A, 126A of the pocket
may be identical to their counterparts in FIG. 1. In the embodiment
of FIG. 4A, dovetail member 122A is non-circular in cross section,
such as oblong. Radius R.sub.1 defines that part of the outer
contour of dovetail member 122A which contacts wall 124A, it being
understood that a similar radius defines the opposing end of
dovetail member 122A. Radius R.sub.2 defines the inner contours of
wall 126A (a similar radius defines the inner contour of wall
124A). In the embodiment of FIG. 4A, the radius of curvature of the
interior wall of the pocket is greater than the radius of curvature
of the exterior surface of dovetail member 122A. These radii and
related dimensions and configuration are selected and arranged such
that contact of dovetail member 122A with the inside surfaces of
walls 124A, 126A occurs along only a portion of the inside surfaces
of walls 124A, 126A. End zones 128A, 130A, 132A, 134A of walls
124A, 126A are not contacted by dovetail member 122A. This leaves
gaps such as gap 136A at zone 130A, corresponding gaps (not
identified by reference numerals) existing at the other end zones
128A, 132A, 134A.
FIG. 4B shows an alternative to the embodiment of FIG. 4A. In the
embodiment of FIG. 4B, the radius of curvature of the interior
walls of the pocket exceeds the radius of curvature of the exterior
surface of the contacting portion of the dovetail member, although
this is achieved in a manner different from that of the embodiment
of FIG. 4A. In FIG. 4B, radius R.sub.1 of dovetail member 122B
originates at the rotational axis of the tool holder. As employed
here, the interior surface is that surface of pocket wall 124B or
126B which contacts the dovetail member 122B.
The aforementioned embodiments all relate to ways of limiting
contact of a dovetail member with pocket walls. The effect of
limiting contact in this manner is that the uncontacted portion of
the walls of the pockets of the embodiments of FIGS. 1, 2, 3, 4A,
and 4B serve to allow tangential deflection of the pocket walls
mitigating radial deflection which would create additional stress
on the pocket walls. In another type of modification, and referring
now to FIG. 5, structure is introduced to accommodate forces acting
on a pocket of a shank 138. The pocket of shank 138 includes two
walls 140, 142 bearing respective driving surfaces 144, 146. In the
view of FIG. 5, driving surfaces 144, 146 are inclined relative to
axis of rotation 148, and thus are visible in this end view.
Orientation of surfaces 144, 146 is such that if hypothetically
extended, as shown by straight projection lines 150, 152, these
projection lines 150, 152 avoid overlying axis of rotation 148.
Surfaces 144, 146 are oriented with respect to the direction of
rotation of shank 138, which as indicated by arrows in FIG. 5 is
counterclockwise. It will be seen that the innermost portion of
surface 144, that being the closer to axis of rotation 148, is the
leading side, whereas the outermost portion of surface 144 is the
trailing side. If the direction of rotation were reversed (although
this embodiment is not shown), then projection line 150 associated
with surface 144 would extend not from the upper left to the lower
right, but rather from the lower left to the upper right. The same
relationships hold true but in mirror image for surface 146. By
contrast, in the prior art devices, driving surfaces corresponding
to surfaces 144 and 146 are generally arranged radially from the
axis of rotation. The modification of the present invention
redistributes forces which would promote greater or more quickly
occurring opening or spreading of the pocket in the prior art
designs.
FIG. 6 shows a modification to the embodiment of FIG. 1. In FIG. 1,
dovetail member 60 has a relief 154 which modifies the otherwise
frustoconical configuration, and an extension 156. This
configuration is modified in the embodiment of FIG. 6 such that an
extension 158 is formed in dovetail member 160 below frustoconical
lateral surface 162 of a cutting head 164. As in the embodiment of
FIG. 1, lateral surface 162 is oriented at an obtuse angle to axis
of rotation 168. Extension 158 has an outer partially cylindrical
surface 166 which is in addition to surface 162, and a recessed
incuse partial surface 170. To accommodate this additional
structure, pocket 172 of shank 174 has surfaces (only surface 176
is visible in FIG. 6) corresponding to surface 166 of extension 158
that do not make contact. Extension 158 also has a beveled or a
radiused surface including partial beveled surface 178 and incuse
partial beveled or radiused surface 180. Pocket 172 has
corresponding surfaces (only radiused surface 182 is visible) to
enable cutting head 164 to be received in pocket 172. In other
respects, both cutting head 164 and shank 174 are similar to their
counterparts in other embodiments.
It would be possible to eliminate cylindrical surfaces 166, 170
from extension 158. As seen in FIG. 7, this is the case in cutting
head 184, which has a dovetail member 186 bearing an upwardly
facing frustoconical surface 188 for interlocking to a pocket of a
shank (not shown), and a downwardly facing frustoconical surface
190. An incuse recess 192 is formed in dovetail member 186. The
shank which is to be used with cutting head 184 would of course
have configured therein surfaces to accommodate surfaces 188, 190,
192 of cutting head 184 to assure secure retention of cutting head
184 by surface 188 and the corresponding surface in the pocket. In
other respects, both cutting head 184 and its associated shank are
functionally and structurally similar to their counterparts in
other embodiments of the invention. It will be appreciated that
surface 190 does not contact the pocket walls.
The effect of the modifications of the embodiments of FIGS. 6 and 7
is to increase the overall length of frustoconical lateral surface
62, which in the embodiment of FIG. 1 is not extended. This
increased length, regardless of whether the added length extends
straight down (surface 166 of FIG. 6) or is tapered (surface 190 of
FIG. 7) allows for a smooth transition between either of the
surfaces corresponding to frustoconical surfaces 162 and 188 (FIGS.
6 and 7) of the pocket in relation to the pocket floor thereby
minimizing stress concentration.
Turning now to FIG. 8, a further embodiment is shown wherein a
cutting head 194 is installed to a shank 196. Cutting head 194 has
a dovetail member 198 bearing an end surface 200. Pocket 202 of
shank 196 is dimensioned and configured to contact base surface 204
of cutting head 194 for resisting compressive axial forces. Contact
with end surface 200 of cutting head 194 is avoided. A shelf 208
and a relief trough 206 are formed in the floor or upwardly facing
central surface of pocket 202. Trough 206 projects into shank 196,
extending towards the trailing end of the tool assembly comprising
cutting head 194 and shank 196. Trough 206 extends across and fully
spans the floor from one flute 222 to opposed flute 224. A better
understanding of the geometry of shank 196 will be obtained by also
referring to FIG. 9. The floor of pocket 202, which floor
collectively encompasses trough 206, shelf 208, and shelf 216,
separates and spaces apart one pocket wall 218 from opposed second
pocket wall 220. Referring especially to FIG. 9, shelves 208, 216
each extend laterally across the floor at respective upper edges
226, 228 of relief trough 206. Each shelf 208 or 216 is associated
with one pocket wall 218 or 220. Relief trough 206 is angularly
oriented relative to rotational axis 230 such that each shelf 208
or 216 intersects only flute 222 or 224, being separated from the
other flute 224 or 222 by trough 206. By way of further
explanation, it will be seen that shelf 216 terminates at the right
side, as depicted in FIG. 9, at flute 224, whereas at the left side
in FIG. 9, shelf 216 is spaced apart from flute 222 by a surface
221 which appears as an upward extension of trough 206.
A consequence of this geometry is that trough 206 has at one end a
curved end edge 210 which meets the side profile 214 of dovetail
member 198 (see FIG. 8) at a tangent at a portion of dovetail
member 198. Curved edge 210 has a significantly greater radius of
curvature than does end edge 212 (see FIG. 8) located oppositely
from end surface 210. The greater radius of curvature provides a
transition in wall thickness which is gentler than the relatively
small curvature seen at edge 212. Stress concentrations are thereby
minimized at the corners of the walls of pocket 202 where dovetail
member 198 terminates near the floor of the pocket at relief trough
206.
It will be appreciated that while the dovetail portion of the
connector of the cutting head is described in terms of being
frustoconical, it would be possible to utilize any configuration
wherein there is an upwardly facing surface which can engage one or
more corresponding surfaces formed in the retaining structure of
the shank. It is preferred to form the dovetail of the connector as
frustoconical merely because rotary machining and other inexpensive
methods may be employed to form the dovetail.
The novel features presented herein may be present in combinations
within a single tool made according to the present invention, where
such embodiments are geometrically compatible, for example surface
221 also reduces the contact area between the dovetail and the
pocket.
It will further be appreciated that relative locations of
connecting and drive structure of the cutting head and of the shank
may be reversed if desired, with appropriate accommodation being
made to account for differences in the directions in which forces
are imposed.
While the invention has been specifically described in connection
with certain specific embodiments thereof, it is to be understood
that this is by way of illustration and not of limitation, and the
scope of the appended claims should be construed as broadly as the
prior art will permit.
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