Small-shank tool for automatic lathes

In a small-shank cutting tool for a Swiss-type automatic lathe, the tool shank defines a square cross-sectional shape having a width of either 7 mm or 8 mm, and a tool recess defined at one end of the shank by two tool-supporting surfaces oriented at an acute angle relative to each other. A rhomboidal-shaped tool insert of the cutting tool is seated within the tool recess of the shank with two sides of the insert each engaging a respective tool-supporting surface of the shank, and a substantial portion of the other two sides of the insert extending beyond the end of the shank and forming a cutting tip for cutting a workpiece. The rhomboidal-shaped insert defines an inscribed circle having a diameter less than approximately 6 mm, and a fastener aperture extending through the approximate center of the inscribed circle defining a diameter less than that of the inscribed circle, in order to provide sufficient space on the shank to form at least two supporting surfaces for engaging and supporting the rhomboidal insert along a substantial portion of each of two sides. A threaded fastener of the cutting tool extends through the fastener aperture and is threadedly attached to the tool shank for fixedly attaching the tool insert to the tool shank. The threaded fastener is preferably a counter-sunk torque screw, and defines a maximum head diameter less than approximately 70% of the diameter of the inscribed circle in order to maintain sufficient structural integrity of the insert to avoid failure during machining operations.

FIELD OF THE INVENTION 
The present invention relates to cutting tools for automatic lathes, and 
more particularly, to such cutting tools having an interchangeable tool 
insert attached to a shank with the insert defining a generally rhomboidal 
shape and having a cutting surface extending beyond the tip of the shank 
for cutting a workpiece, and particularly suited for use with small-shank 
cutting tools having shanks less than 9 mm in width. 
BACKGROUND INFORMATION 
In a typical Swiss-type automatic screw machine, a plurality of cutting 
tools are radially disposed about a sliding headstock for cutting a 
workpiece which is rotatably and longitudinally driven relative to the 
tools. The cutting tools are typically comprised of a tool bit or insert 
attached to a tool holder or shank, and the shanks are selectively 
actuated to move the tools radially into and out of engagement with a 
workpiece to cut the workpiece as desired. 
The tool shanks are typically made of rectangular-shaped bars which are 
slidably mounted within corresponding channels formed in a tool turret or 
gauge plate mounted around or above the headstock. The tool shanks are 
provided in the following industry-standard widths: 7 mm, 8 mm, 10 mm, 12 
mm, 5/16 inch, and 1/2 inch. Most smaller automatic screw machines can 
accommodate only the 7 and 8 mm width shanks (referred to herein as 
"small-shank" cutting tools), whereas the larger automatic screw machines 
use the shanks having widths of 10 mm or larger. 
Cutting tools having a shank width of 8 mm or larger are commercially 
available in several different configurations. In one type, the carbide 
tool bits are brazed to the ends of the shanks. In another type, 
interchangeable carbide tool inserts are screwed or clamped to the ends of 
the shanks. One advantage of the brazed cutting tools, is that they are 
relatively less expensive to manufacture and the tool bits are strongly 
secured in place. One advantage of the interchangeable tool inserts, on 
the other hand, is that the inserts are provided with more than one 
cutting edge so that when each edge becomes worn, chipped or otherwise 
requires replacement, the tool insert may be relatively quickly rotated or 
indexed on the shank by adjusting the fastener or clamp to position a 
fresh cutting edge of the insert into a cutting position. The clamping 
mechanisms may provide a secure lock; however, they are relatively bulky 
and may not always be easily mounted within the screw machines, 
particularly the machines requiring small-shank tools, and may therefore 
require additional set-up time and installation expense. 
Currently, most cutting tool manufacturers provide the same series of tool 
inserts for use with each of the respective manufacturer's available 
shanks. In addition, most manufacturers only provide interchangeable tool 
inserts for tools having shank widths of 10 mm or larger. For cutting 
tools having shank widths of less than 10 mm, these manufacturers 
recommend the use of brazed tools, as described above. One drawback of the 
brazed tools, however, is that once the tool bits become worn, they must 
be ground to reform the cutting edges, or the entire tools must be 
replaced, and the machine must be reset to accept the re-ground tool. The 
inventor of this application is not aware of any manufacturer that has 
provided cutting tools with interchangeable inserts for shank widths of 
less than 8 mm, and he is aware of only one manufacturer that has provided 
cutting tools with interchangeable inserts for shank widths of 8 mm. 
Referring to FIG. 1, a typical such commercially-available cutting tool is 
indicated generally by the reference numeral 1. The cutting tool 1 
includes a rectangular-shaped shank 2 having a width of 8 mm, and a 
rhomboidal-shaped (or diamond-shaped) insert 3 attached to one end of the 
shank by a screw 4. As can be seen, the tool insert 3 is defined by an 
inscribed circle which is approximately equal to the width of the shank 2 
(8 mm), and the shank defines a single tool-supporting edge 5 for engaging 
and supporting a corresponding edge of the tool insert. One of the 
problems encountered with this configuration is that if the insert is 
torqued in the clockwise direction in FIG. 1, the tool insert may become 
relatively easily dislodged on the shank, thus rendering the cutting tool 
ineffective and requiring time-consuming breakdown and set-up to either 
repair or replace the tool. 
As illustrated in broken lines in FIG. 1, industry has attempted to 
overcome this problem by providing the shank with another, smaller 
supporting edge 5' on the opposite side of the tool insert relative to the 
first supporting edge 5. However, because of the size and location of the 
second supporting edge, it provides little additional support and has 
proven to break away relatively easily, and has otherwise failed to 
effectively prevent the insert from being dislodged when torqued in the 
clockwise direction in FIG. 1. 
Accordingly, the prior art has failed to provide an acceptable small-shank 
cutting tool with interchangeable, rhomboidal-shaped tool inserts, and it 
is an object of the present invention to provide such a cutting tool which 
overcomes the drawbacks and disadvantages of the above-described prior 
art. 
SUMMARY OF THE INVENTION 
The present invention is directed to a small-shank cutting tool for an 
automatic lathe, comprising a tool shank defining a rectangular 
cross-sectional shape having a maximum width of less than approximately 9 
mm, and preferably either 7 mm or 8 mm, and including a tool recess 
defined at one end of the shank by two tool-supporting surfaces oriented 
at an acute angle relative to each other. One of the tool-supporting 
surfaces is generally parallel to an adjacent side of the shank, and the 
shank defines an elongated body portion extending between the respective 
tool-supporting surface and side of the shank having a thickness of at 
least approximately 1.0 mm for enhancing the structural integrity of the 
respective tool-supporting surface. A rhomboidal-shaped tool insert of the 
cutting tool is seated within the tool recess of the shank with two sides 
of the insert each engaging a respective tool-supporting surface, and a 
substantial portion of the other two sides of the insert extending beyond 
the end of the shank and forming a cutting tip for cutting a workpiece. 
The rhomboidal-shaped insert defines an inscribed circle having a diameter 
less than approximately 90% of the maximum shank width, and a fastener 
aperture extending through the approximate center of the inscribed circle 
defining a diameter less than approximately 70% of the diameter of the 
inscribed circle. A threaded fastener of the cutting tool extends through 
the fastener aperture and is threadedly attached to the tool shank for 
fixedly attaching the tool insert to the tool shank. The threaded fastener 
defines a counter-sunk head having a maximum diameter less than 
approximately 70% of the diameter of the inscribed circle, in order to 
maintain sufficient structural integrity of the insert to avoid failure 
during machining operations. 
One advantage of the present invention is that an interchangeable, 
rhomboidal-shaped insert may be used with either 7 mm or 8 mm width 
shanks, and the shank engages and supports such inserts along a 
substantial portion of two sides of the insert to fixedly secure the 
insert and prevent the insert from being dislodged or rendered defective 
in a like manner as encountered with the prior art small-shank cutting 
tools described above.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
In FIGS. 2 and 3, a typical tool holder or shank embodying the present 
invention is indicated generally by the reference numeral 10. The shank 10 
is adapted to hold one or more interchangeable tool inserts, shown 
typically at 12 FIG. 4, for use in an automatic screw machine, and is 
particularly suitable for use in "small-shank" screw machines that can 
only accommodate shanks having widths of less than 9 mm. Currently, the 
industry standard shank widths for such "small-shank" machines are 7 mm 
and 8 mm. 
As shown in FIG. 2, the shank 10 defines an elongated or 
longitudinally-extending body 14 having a rectangular cross-sectional 
configuration. In the embodiment of the present invention illustrated, 
each of the four sides of the body 14 define an equal width "A" forming a 
square cross section. One end of the body 14 of the shank defines a tool 
recess 16 for receiving and supporting a tool insert 12 (FIG. 4), as is 
described further below. The recess 16 is defined by a first 
tool-supporting surface 18, a second tool-supporting surface 20, and a 
base surface 22 extending between the first and second surfaces and 
oriented normal to these surfaces. As shown in FIG. 2, the first and 
second tool-supporting surfaces 18 and 20 are oriented at an acute angle 
"B" relative to each other, and the outermost end of each tool-supporting 
surface is oriented tangential to an inscribed circle "IC" defined by each 
tool insert 12 (FIG. 4). 
As can be seen in FIG. 2, the first and second tool-supporting surfaces 18 
and 20 are positioned on the body 14 so as to define an elongated lip or 
supporting body section 24 behind the second tool-supporting surface 20 
and having a thickness "C". In order to provide adequate support for the 
tool insert when received in the recess 16 and to otherwise ensure the 
structural integrity of the cutting tool, the thickness C of the lip 24 is 
preferably at least approximately 1.0 mm for a shank having a width A of 
approximately 7 mm, and may be thicker for larger-width shanks. As also 
shown in FIG. 2, the shank 10 defines a relief pocket 26 formed at the 
innermost ends of the first and second tool-supporting surfaces 18 and 20. 
Turning to FIG. 4, the interchangeable tool insert 12 has four sides 
forming a substantially rhomboidal or diamond shape, including two 
parallel first sides 28 and two parallel second sides 30. Each first side 
28 of the insert is oriented at an acute angle B relative to a respective 
second side 30, and the adjacent pairs of first and second sides each form 
a respective cutting tip 32 having a depth "D", as shown in FIG. 4. Each 
cutting tip 32 defines one or more respective cutting edges which are 
shaped and configured in accordance with the particular type of machining 
operation to be performed, as is described further below. For example, as 
shown in FIG. 4, a chamfer is formed at the juncture of each respective 
pair of first and second surfaces 28 and 30, respectively. The tool insert 
12 is preferably made of carbide steel, but may equally be made of other 
desired materials. 
The angle B of the tool insert shown in FIG. 4 is the same as the angle B 
of the shank shown in FIG. 2 so that when the insert is received within 
the recess 16 of the shank, the respective first and second surfaces 28 
and 30 are seated in conforming engagement with the first and second 
tool-supporting surfaces 18 and 20 of the shank, respectively, to securely 
support the insert on two sides. In the embodiment of the present 
invention illustrated, the angle B is approximately 35.degree.; however, 
as will be recognized by those skilled in the pertinent art, this angle 
may changed as desired depending upon the requirements of a particular 
cutting tool design or other machining system. When the tool insert 12 is 
received within the recess 16 of the shank, preferably substantially the 
entire depth D of the respective cutting tip 32 extends beyond the end 
surface 33 of the shank (FIGS. 2 and 3), as is described further below. 
As shown in broken lines in FIG. 4, the insert 12 defines an inscribed 
circle "IC", which is defined by the diametrical distance between either 
the opposing first sides 28 or the opposing second sides 30 of the insert. 
In the embodiment of the present invention illustrated, the tool insert 12 
is designed for tool shanks having a width A of 7 mm or greater, and 
therefore the diameter of the inscribed circle IC is approximately 6 mm. 
Accordingly, in a shank 10 having a width of 7 mm, the thickness C of the 
supporting lip 24 is approximately 1 mm, and in larger-width shanks the 
thickness C may be greater. In accordance with the present invention, for 
such small-width shanks (i.e., 8 mm or less), the diameter of the 
inscribed circle IC should be no more than approximately 90% of the width 
A of the shank, and for 7 mm shanks, the diameter of the inscribed circle 
IC is preferably approximately 86% or less of the shank width, in order to 
ensure that the lip 24 has sufficient thickness and structural integrity 
to fixedly support the tool insert during machining operations. 
Accordingly, the diameter of the inscribed circle IC is preferably within 
the range of approximately 5.5 mm to 6.5 mm for shanks having a width 
within the range of approximately 7 mm to 8 mm. 
As also shown in FIG. 4, the tool insert 12 defines a counter-sunk aperture 
34 extending through the approximate center of the inscribed circle IC for 
receiving a threaded fastener 36 (FIG. 5) to fixedly attach the insert to 
the shank. The counter-sunk aperture 34 defines a maximum diameter E which 
is sufficiently less than the diameter of the inscribed circle IC of the 
insert to maintain its structural integrity. As shown in FIG. 5, the 
threaded fastener 36 is preferably a counter-sunk torque screw defining a 
maximum head diameter E, which is approximately the same as the maximum 
diameter E of the counter-sunk aperture 34 of the tool insert. In this 
embodiment of the invention, wherein the tool insert defines an inscribed 
circle IC having a diameter of approximately 6 mm, the diameter E should 
be no more than approximately 4 mm, and is preferably approximately 3.5 
mm. However, as will be recognized by those skilled in the pertinent art, 
the diameter E may be changed as required depending upon the inscribed 
circle of the insert. In accordance with the present invention, for tool 
inserts having an inscribed circle IC of approximately 6 mm or less, the 
diameter E should be no more than approximately 70% of the diameter of the 
inscribed circle. Similarly, for the insert of the invention wherein the 
diameter of the inscribed circle IC is within the range of approximately 
5.5 mm to 6.5 mm for shank widths within the range of approximately 7 mm 
to 8 mm, the maximum head diameter E will be within the range of 
approximately 3 mm to 4.5 mm depending upon the specific minimum shank 
width and inscribed circle selected. 
Also with reference to FIG. 5, in this embodiment of the invention the 
angle F of the conical-shaped surface 38 of the fastener head is 
approximately 60.degree. (the "counter-sink angle"); however, as will be 
recognized by those skilled in the pertinent art, this angle may be 
changed within limits depending upon the requirements of a particular 
cutting tool design or other machining system. In accordance with the 
present invention, the angle F is preferably within the range of 
approximately 52.degree. to 68.degree. minimize the overall head diameter. 
As will also be recognized by those skilled in the pertinent art, the 
surface angle of the counter-sink aperture 34 is selected to substantially 
match the angle F of the fastener 36 and is preferably configured so that 
when the fastener is received within the aperture and threadedly engaged 
with the shank, the top of the fastener is at approximately the same level 
as the top edge of the aperture. 
As shown in FIGS. 2 and 3, the shank 10 defines a threaded bore 40 for 
threadedly receiving the fastener 36 upon attachment of the tool insert 12 
to the shank. The threads of the fastener and bore are preferably 
relatively fine, and in the preferred embodiment illustrated a "M2.5-4H" 
thread is employed (2.5 mm pitch.times.4 threads per mm). Accordingly, the 
tool insert 12 is seated within the recess 16 of the shank with a 
respective first side 28 of the insert engaging the first tool-supporting 
surface 18, and the adjacent second side 30 of the insert engaging the 
second tool-supporting surface 20 of the shank. The fastener 36 is then 
inserted through the counter-sunk aperture 34 of the insert and threadedly 
engaged within the threaded bore 40 of the shank to fixedly secure the 
insert to the shank. 
As mentioned above, the cutting tip 32 of each insert 12 may take any of 
several different shapes and/or configurations, depending upon the type of 
machining operation to be performed. For example, as shown typically in 
FIG. 7, the cutting tip 32 of the insert 12 may be ground or otherwise 
shaped in the several different configurations shown to perform front 
turning, back turning, cut off, threading, plunge and turning, and 
grooving operations. On the upper side of the workpiece in FIG. 7, the 
three exemplary cutting tools of the invention are shown in bottom plan 
view, whereas on the lower side of the workpiece the three cutting tools 
are shown in top plan view. 
One advantage of the cutting tool of the present invention is that because 
the diameter of the inscribed circle IC is preferably less than 
approximately 6 mm, for small-width shanks having a width of 8 mm or less, 
there is sufficient space to one side of the tool insert when attached to 
the shank to provide a second tool-supporting surface and lip for engaging 
and supporting the rhomboidal insert on two sides. Accordingly, the 
problems associated with the prior art small-shank cutting tools with 
interchangeable inserts are substantially avoided. 
As will be recognized by those skilled in the pertinent art, numerous 
changes and modifications may be made to the above-described and other 
embodiments of the present invention without departing from its scope as 
defined in the appended claims. Accordingly, this detailed description of 
a preferred embodiment is to be taken in an illustrative, as opposed to a 
limiting sense.