The invention relates to a toolholder for holding a tool at one end and having a tubular shank at its other end for mounting it into the bore of a support member. The shank has at least two circumferentially spaced perforations in its tubular wall. Each of the perforations extends obliquely toward the front of the shank as it extends from the inner to the outer surface of the tubular wall. A locking element is located partially within each of said perforations and the recess formed by the inner surface of the tubular shank. An actuating mechanism is located within the recess to drive the locking elements outwardly against the walls, thereby expanding the rear of the tubular shank to lock the shank in the support member bore.

BACKGROUND OF THE INVENTION 
This invention relates to toolholders. It is especially concerned with a 
body having at least one cutting insert seat on one end and a shank 
receivable in the bore of a tool support member on the other end. Such 
tools are used in the cutting and shaping of workpieces where it is 
important that the toolholder be held in a rigid manner so that both 
movement and vibration are minimized during the metalcutting operation. 
Many devices in the prior art have proven to be successful in this regard 
and are exemplified by McCreery U.S. Pat. Nos. 3,498,653; McCray et al 
4,135,418; Heaton et al 4,197,771; and Friedline 4,350,463. The foregoing 
devices are concerned with the use of ball-like locking elements to hold 
the shank of a toolholder in the bore of the tool support member. 
One drawback common to the foregoing designs is the feature that the 
locking elements in each must abut against at least one surface during 
locking that is not similar in size and shape to the locking element 
abutment surface. This produces small contact areas with high contact 
stresses leading to plastic deformation of the locking elements and the 
surfaces they abut against each time the toolholder is locked onto a 
support member. After many repeated uses, the deformation in the locking 
elements and the surfaces they abut against can lead to a reduction in the 
rigidity of the toolholder, thus shortening its useful lifetime. 
There is, therefore, clearly a need for a toolholder and a toolholder 
assembly design which has a longer lifetime. This design must, however, be 
capable of being easily and accurately manufactured. It should also be 
capable of being compactly sized so that it can be used in a wide range of 
applications, including small diameter boring bars. 
SUMMARY OF THE INVENTION 
I have surprisingly found that the present invention addresses the 
foregoing needs in that a toolholder is now provided that has a long 
lifetime, and yet can be made compactly and is also both easily and 
accurately manufactured. 
In the present invention, a toolholder shank for mounting in a bore through 
a forwardly facing surface of a tool support member is provided. The shank 
has a tubular portion which is perforated by perforations at at least two 
circumferentially spaced locations. Each of these perforations contains a 
forwardly facing concave abutment surface which extends forwardly while 
extending from the inner surface toward the outer surface of the tubular 
shank. 
In a preferred embodiment, the shank is an integral part of a toolholder 
having a forward end for receiving a tool. The toolholder also has a 
rearwardly facing abutment face for abutment with the tool support member 
surface that contains the bore in which the toolholder shank will be 
received. In addition, a key or keyway is present on the toolholder for 
holding the tool nonrotatable with respect to the tool support member. 
Furthermore, a section of the tubular shank portion located rearwardly of 
the forwardly facing concave abutment surfaces is resiliently expansible 
for abutment with the support member bore. 
Preferably, the forward facing abutment surfaces in the perforations are 
concave, and more preferably, are concave cylindrical surfaces. Most 
preferably, these abutment surfaces have a radius of curvature which is at 
least equal to, but no greater than, about 0.004 inches, and more 
preferably about 0.002 inches, larger than the radius of curvature of the 
convex spherical abutment surfaces of the locking elements which will abut 
against these toolholder surfaces. 
Preferably, the outer surface of the tubular shank portion tapers inwardly 
as it extends rearwardly, and more preferably, the outer surface is a 
frustoconical surface. 
Preferably, the mechanism for holding the toolholder nonrotatable is one or 
more slots or keyways in the rear of the tubular shank which are designed 
to receive one or more keys in the bore of the tool support member.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the present invention, FIG. 1 shows an embodiment of a 
toolholder 10 having a forward end 12 and a rearward tubular shank 16 
attached to the forward end 12. On the forward end 12 is a pocket 14 for 
receiving a cutting tool. The pocket 14 is conventional in design and is 
designed to receive an indexable cutting insert, locking pin and shim (not 
shown). It should be understood, however, that the present invention is 
not limited to the forward end design shown in FIG. 1, but includes by way 
of example and not limitation forward ends having multiple insert seats 
such as may be found on a milling cutter. In addition, the forward end may 
be a non-cutting tool. 
At the juncture of the forward end 12 and the shank 16 is a rearwardly 
facing abutment face 15 for abutment with the forwardly facing surface of 
a tool support member. Preferably, face 15 is planar and is oriented at 90 
degrees to the longitudinal center line X--X of shank 16. 
As shown in FIG. 1, the tubular shank 16 is preferably an integral part of 
the toolholder 10, and is preferably machined from a single piece of 
steel. However, it is also contemplated that the tubular shank 16 and the 
forward end 12 of the toolholder may be independent pieces that may be 
subsequently mechanically joined together with the rearwardly facing 
abutment face 15 being a part of either the forward end 12 or the shank 
16. In this manner, a single shank may be utilized with a variety of 
different toolholders or other tool components. 
The shank design of the present invention may also be used in segments, 
extensions or assembly components of a modular boring system. In fact, it 
is envisioned that the present shank design may be used in a plurality of 
segments to join one segment to the next. 
As shown in FIG. 1, the tubular shank 16 has a frustoconical shape and is 
perforated at two circumferentially spaced locations by perforations 18, 
the walls 20 of which communicate with shank inner surface 22 and outer 
surface 24. While preferably, as shown in FIG. 1, the tubular shank has 
two perforations 18 circumferentially spaced at 180 degrees to each other, 
it may be desired in large shank diameters that there be three or four 
circumferentially spaced perforations 18. 
Circumferentially spaced between perforations 18 are slots 26 and 28 on the 
end of the tubular shank 16. These slots 26 and 28 are designed to serve 
as keyways to accept keys in the tool support member bore and thereby hold 
the toolholder nonrotatable with respect to the tool support member. In 
addition, by locating the slots at the rear end of the tubular shank, the 
flexibility of the portion of the shank behind the perforations can be 
readily controlled by changes in the location, size and number of slots. 
In the embodiment shown in FIG. 1, only slot 26 located in line with the 
cutting tool receiving pocket 14 is utilized as a keyway to hold the 
toolholder nonrotatably insofar as the width, w, of slot 26 is dimensioned 
to provide a slip fit with a key whereas the width of slot 28 is slightly 
larger (e.g., 0.010 inches greater) than the width of slot 26. This 
provides the added benefit that the tubular shank can be readily received 
in a tool support bore provided with two keys in order to accept both 
right handed and left handed toolholders (i.e., cutting tool pocket on the 
left or right hand side of the toolholder). 
In an alternative embodiment (not shown) the location of the perforations 
18 and slots 26 and 28 may be rotated ninety degrees from that shown in 
FIG. 1 about the longitudinal axis X--X of the shank so that one of the 
perforations 18 is aligned with the cutting tool receiving pocket 14. 
In accordance with the present invention, the toolholder 10 is mounted on a 
tool support member 30 via locking elements 32. As shown in FIG. 2., these 
locking elements 32 preferably are two spherical balls (i.e., spheres) 
which are held partially within the perforations 18 by a locking rod 34 
nonrotatably contained within a longitudinal passageway 36 in stub 38. The 
locking rod 34 has two cylindrical shaped ramps 40 which drive the balls 
32 outwardly through radial apertures 42 in stub 38 when the locking rod 
34 is pulled rearwardly as shown in FIG. 2. 
As the locking balls are moved outwardly by ramps 40, they are driven into 
abutment with the forwardly facing abutment surfaces 44 in perforations 18 
and rearwardly facing concave surfaces 46 in the radial apertures 42 of 
the stub 38. In this manner, a rearwardly force is directed against the 
toolholder 10 such that the rearwardly facing abutment shoulder 15 on the 
toolholder 10 is placed in pressurized abutment with the forward facing 
surface 50 of the tool support member 30. 
At the same time that this is occurring, the locking elements 32 in 
addition to exerting a rearwardly directed force also exert an outwardly 
directed force against the forwardly facing abutment surfaces 44 in 
apertures 18 and thereby resiliently expand the sections 52 of the shank 
outer surface 24, located rearwardly of abutment surfaces 44, into 
abutment with the bore 48 of the tool support member 30. 
Also shown in FIG. 2 is the engagement between key member 54 and slot 26 
which act to hold the toolholder 10 nonrotatable with respect to the tool 
support member. These members are circumferentially located at 90 degrees 
to perforations 18. 
These various components of the toolholder assembly, in accordance with the 
present invention, are shown more clearly in the remaining figures. 
In FIG. 3, which is a cross section taken through the tubular shank 16 
along a plane containing a shank diameter and the center lines P--P of 
perforations 18, it is clearly shown that perforations 18 preferably form 
walls 20 that are cylindrical in shape and have a radius of curvature 
r.sub.c. These perforations 18 are angled with respect to the longitudinal 
center line X--X of the shank at an angle B such that the rotational axis 
of symmetry P--P, and more importantly, forwardly facing concave abutment 
surfaces 44 on walls 20 extend forwardly while extending away from the 
inner surface 22 toward the outer surface 24 of the tubular shank 16. 
While it would be preferred that angle B is as large as possible to 
maximize mechanical advantage, at large angles, machining tolerances may 
interfere with the proper locating of the locking elements 32 against 
surfaces 44. It is, therefore, preferred that angle B is 50 to 60 degrees. 
Concave forwardly facing abutment surfaces 44 have a radius of curvature 
r.sub.c, the value of which is determined by the radius of curvature, 
r.sub.s, of the concave abutment surface of the locking elements 32 which 
will abut against surfaces 44 (see FIG. 2). It is preferred that r.sub.c 
and r.sub.s be as close as possible to each other so that, when the 
locking elements 32 are abutted against surfaces 44, contact occurs over 
as large an area as possible in order to minimize deformation to the 
surface 44 and to the locking element surface, thereby prolonging their 
useful lifetimes. Preferably, in order to achieve this result, it is 
preferred that r.sub.c is equal to, but no greater than, 0.004 inches, and 
more preferably 0.002 inches,larger than r.sub.s. 
It is important that the abutment surfaces 44 have the radius and slope 
described. It is also important that abutment surfaces 44 be at the same 
height in a direction parallel to the X--X axis to assure lockup occurs in 
both abutment surfaces. However, the other portions of the perforation 
walls 20 that are not used for abutment with the locking elements may 
deviate from the above described relationships without affecting the 
performance of the present invention. Nonetheless, from the point of view 
of manufacturing ease, it is preferred that the entire surface of 
perforation walls 20 have the r.sub.c and B described above in that the 
perforations 18 may be simply and accurately made by drilling holes with a 
twist drill or by milling with an end mill of the required diameter held 
at the appropriate angle at the same distance from rearwardly facing 
abutment face 15. 
The outer diameter of the tubular shank 16 decreases as the shank extends 
rearwardly. Preferably, this decrease is gradual and provides outer 
surface 24 with a frustoconical shape as shown in FIG. 1. The angle, A, 
that surface 24 forms with the shank center line X--X, while preferably as 
small as possible in order to minimize shank diameter for use with small 
diameter support members (e.g., small diameter boring bars), must be large 
enough to allow the shank to be easily loaded into the bore 48 of the tool 
support member 30 which has an angle of taper slightly larger (e.g., 5 
minutes of arc) than angle A as shown in FIG. 2. I have found that setting 
angle A equal to four degrees adequately addresses both concerns. 
An internal cavity 56 is formed in tubular shank 16 by inner generally 
cylindrical surface 22 which is joined by rearwardly facing surface 58 at 
the forward end of the tubular shank. The cavity 56 has been sized to 
loosely accept the lock up mechanism shown in FIG. 2. At its rearmost end, 
surface 22 is joined by a radially outwardly flaring surface 60 which 
extends to the rear surface 61 which joins it and outer surface 24. The 
outwardly flared surface 60 serves to ease loading of the tubular shank 16 
over stub 38. 
FIG. 4 shows an exploded view of the components shown in FIG. 2, with the 
toolholder 10 and locking pins 32 removed for clarity. The tool support 
member 30 is shown having forwardly facing abutment surface 50 perforated 
by bore 48. The bore surface 62 in the forwardmost section tapers inwardly 
toward the center line of the bore 48 at an angle which is slightly larger 
than angle A on the tubular shank 16 as it recedes from forward face 50 
until it joins cylindrical bore surface 64. The bore 48 is preferably 
perforated through its forward tapered surface 62 by two diametrically 
opposed apertures 66 which hold cylindrical keys 54 which are press fit in 
apertures 66 and which extend into bore 48. The support member further 
contains holes 68 (only one of which is shown) for receiving bolts (not 
shown) for joining support member 30 to a larger machine tool (not shown), 
such as a lathe turret, spindle, boring bar, etc. It should be further 
understood that support member 30 may be an integral part of, and not 
separate as shown, of such a turret, spindle, boring bar, etc. 
The locking element actuating mechanism includes the lock rod 34 and the 
stub 38. The lock rod 34 has an abutment member 70 joined to an attachment 
member. Attachment member is shown here as externally threaded rod 72. The 
abutment member 70 has an end surface 74 joined to an oppositely facing 
shoulder 76 by a side surface 78. Preferably, the end surface 74 may be 
used for abutment against surface 58 of the toolholder 10 when the locking 
rod is pushed forward to unlock the toolholder 10 from the tool support 
member 30. In this manner, lock rod 34 and end surface 74 may be used to 
lift the toolholder 10 off the support member 30. 
Side surface 78 is a cylindrical surface which has been intersected by 
radially outward facing concave surface depressions 80 which are 
equidistant from end surface 74 and circumferentially spaced at 180 
degrees to each other. These depressions 80 have been dimensioned to 
receive locking elements 32 in the unlocked position. The depressions 80 
as shown are elongated in the direction of the longitudinal axis Y--Y and 
preferably have a concave spherical surface at each longitudinal end with 
a radius r.sub.1 that is equal to or slightly larger than the radius of 
the locking element 32. The radial depth of depressions 80 into 
cylindrical side surface 78 is set so that the sum of the thickness of 
lock rod material separating depressions 80 plus the two diameters of the 
locking elements 32 is less than the internal diameter of the shank. 
As most clearly shown in FIG. 5, joining depressions 80 at the same 
longitudinal end of each depression are ramps 40, one for each depression 
80. Each ramp 40 declines inwardly toward central axis Y--Y as it extends 
away from end 74 until it joins depressions 80. The surface of ramp 40 is 
a concave cylindrical surface of revolution having a radius r about an 
axis Z--Z tilted on an angle C to central axis Y--Y. Radius r is again 
equal to or slightly larger than the radius of the locking element 32 and 
is preferably no greater than 0.004 inches, and more preferably 0.002 
inches, larger than r.sub.s. 
While angle C should ideally be as small as possible to maximize mechanical 
advantage, this ideal configuration must be balanced against the ability 
to manufacture within a given tolerance and the concern that the shallower 
C is the longer the ramp becomes and the longer the lock rod must be. I 
have found that setting angle C equal to 20 degrees to be a preferred 
compromise between these competing concerns, with angle C being equal to 
15 degrees being more preferred. 
The radial depth into the lock rod at which the ramps 40 intersect 
depressions 80 is deep enough to assure that the lockup always takes place 
on ramps 40 and not at the intersection of the ramps 40 and the 
depressions 80 or within depressions 80. However, the maximum value that 
the aforementioned radial depth may be designed to have is preferably 
limited to reduce the length of travel of the lock rod required to achieve 
lockup 
As shown in FIGS. 2 and 4, the diameter of lock rod 34 has been dimensioned 
to loosely engage in longitudinal passageway 36 communicating between the 
front surface 82 and the rear surface 84 of stub 38. When engaged in 
passageway 36, lock rod 34 is held non-rotatable by the engagement of 
keyway 86 and key 88 which extends into passageway 36. Key 88 may be a set 
screw 90 threadedly engaged with a threaded radial aperture 92 in stub 38. 
When engaged in the stub 38, the lock rod is reciprocally movable forwardly 
and rearwardly and is held captive between forward facing annular shoulder 
94 and key 88. It should be understood, however, that in alternative 
embodiments the means by which the lock rod 34 is held nonrotatable and 
captive within the stub 38 may be by members external to the lock rod 34 
and/or stub 38. 
When fully engaged in the stub 38, the threaded rod 72 of the lock rod 34 
is engaged with another member (not shown) which will act to reciprocate 
the lock rod forwardly, for unlocking, and rearwardly, for locking. In 
addition, when fully engaged in stub 38, the diametrically opposed 
depressions 80 will align with diametrically opposed radial apertures 42 
which communicate between the side surface 96 of stub 38 and passageway 
36, when the lock rod 34 is in the unlocked position. In the locked 
position, ramps 40 will align with apertures 42 as shown in FIG. 2. 
An annular groove 98 is formed in side surface 96 in a location on the stub 
38 such that it intersects the rearward end of apertures 42. Contained in 
the groove 98 is an elastomeric O ring 100 which is used to retain the 
locking elements 32 within apertures 42 when in the unlocked position. 
Flange 102 of the stub 38 is pierced by longitudinal holes (not shown) for 
accepting bolts (not shown) for mounting the stub 38 on the tool support 
member 30. 
The combination of locking elements 32, locking rod 34 and stub 38 forms 
the locking mechanism, and this mechanism is then joined to a tool support 
member 30 via bolts which are not shown. The locking mechanism sits within 
a tapered bore of the tool support member. The tapered bore preferably 
contains two keys 54 which are located at 180 degrees to each other and at 
90 degrees to the locking elements 32. Keys 54 fit within the slots 24 and 
26 on the end of the tubular shank 16. 
Additional preferred embodiments of shanks, toolholders and other 
toolholder components are described in my copending application Ser. Nos. 
007,070; 007,169; 007,309; and 007,310 filed concurrently with the 
present application. 
All patents and patent applications previously referred to in this 
application are hereby incorporated by reference. 
Changes and modifications in the specifically described embodiments can be 
carried out without departing from the scope of the invention which is 
intended to be limited only by the scope of the appended claims.