Endmill adapter with torque reducing locknut and collet interface

A toolholder 1 of the type including a collet 5 integrally formed with a shank 3 is provided with an interface between a locknut 7 and collet 13 which substantially reduces the torque required to turn the locknut 7 into a position which radially collapses the collet segments 17. In this interface, one of either the inner locknut surface 23 or the outer surfaces of the collet segments 17 includes an engaging portion 56 for wedgingly flexing the collet segments 17 inwardly when the locknut is turned, and a non-engaging portion 58 disposed between the engaging portion 56 and the shank mounted ends of the collet segments 17. The non-engaging portion 58 reduces the torque required to turn the locknut 7 by reducing the binding forces that would otherwise occur between the ends of the collet segments 17 and the inner locknut surface 23. To further reduce torque, the collet portion interconnecting the collet segments 17 with the shank 3 of the toolholder is rendered thinner by the provision of circumferential grooves 72, 76 that make the collet segments 17 more flexible. Sealing rings 66, 74, 81 are seated in grooves 68, 72, 76 present in the interior defined by the collet segments 17 in order to prevent errant flows of coolant or debris from collecting between the collet segments 17 and the tool shank 9 gripped thereby.

BACKGROUND OF THE INVENTION 
This invention generally relates to toolholders, and is specifically 
concerned with an endmill adapter of the type having an integral collet 
that has been improved by the provision of a torque reducing locknut and 
collet interface. 
An endmill is a generally cylindrical cutting tool which has a plurality of 
cutting edges around its outer periphery. The endmill usually includes a 
cylindrical shank which fits into an axial bore of a toolholder. For 
precision cutting operations, the endmill shank must be securely and 
concentrically mounted within the toolholder bore. To this end, various 
mechanisms have been developed for securing the endmill and the toolholder 
against axial movement and against rotation of the endmill with respect to 
the holder. One prior art securing mechanism employs a set screw 
threadedly engaged in the wall of the holder which is tightened against a 
flat formed on the shank of the endmill. Unfortunately, the radial set 
screw creates an imbalance in the holder which creates unwanted vibration 
and eccentric movements of the tool during use, particularly at high 
rotational speeds. Still another prior art securing mechanism has been the 
combination of a collet and chuck. A tapered collet having an axial bore 
for receiving the shank of the endmill is radially compressed by a locknut 
that is threadedly connected to the body of the toolholder. In theory, the 
collet collapses uniformly around its circumference so that the shank of 
the tool is accurately positioned at the center of the holder. A 
non-pullout wedge may be used in combination with the collet to prevent 
axial and rotational movement of the shank of the endmill relative to the 
interior of the collet. A collet and chuck arrangement of this type is 
disclosed in U.S. Pat. No. 4,341,006 to Starn. However, the interfacing 
surfaces of the collet and chuck body require a substantial amount of 
accurate machining which translates into substantial manufacturing costs. 
Further, the cumulative tolerances between parts limit the degree of 
accuracy which can be obtained. 
To overcome the shortcomings associated with the use of prior art set screw 
and collet and chuck mechanisms, engineers employed by Kennametal Inc. 
developed an endmill adapter having an integral collet described and 
claimed in U.S. Pat. No. 5,234,296 by Presby and Mogilnicki. The 
collapsible segments of the collet disclosed in the '296 patent are formed 
by cutting longitudinal slots into an integrally formed, frustro-conical 
skirt extending down from the tapered shank of the toolholder. The 
longitudinal slots do not extend all the way to the ends of the collet 
segments, which has the effect of forming a continuous tie ring that 
integrally joins the distal ends of all of the collet segments. The base 
of the resulting collet is then threaded for receiving the threaded 
interior of the locknut. The resulting collet is easy and inexpensive to 
manufacture, and the continuous tie ring that interconnects the distal 
ends of the collet segments provides greater rigidity at the outer end of 
the collet for improved accuracy. In use, a generally tubular locknut 
having a threaded inner diameter is screwed over the threads at the base 
of the collet for deflecting the collet segments radially inward to grip 
the shank of an endmill or tool. 
While the endmill adapter disclosed and claimed in the '296 patent 
constitutes a substantial advance in the art, the inventors have noted 
several areas where this collet might be improved. For example, while the 
greater rigidity of the collet segments defined by the longitudinal cuts 
in the frustro-conical collet body does indeed improve the accuracy with 
which this device grips and centers the shank of an endmill, the resulting 
rigidity of the collet segments also increases the amount of torque 
necessary to turn the locknut to adequately radially deflect the segments 
into firm engagement with a tool shank. Additionally, as is the case with 
other prior art collet chuck mechanisms, it may be possible for errant 
sprays of coolant to enter the chuck mechanism and flow between the tool 
shank and the interior surface of the collet. The presence of liquid 
coolant between the interior surface of the collet and the tool shank 
secured therein is undesirable, as it can interfere with the desired 
frictional grip between these two components. 
Clearly, what is needed is an improved endmill adapter of the type that 
utilizes an integral collet in which the locknut can be turned in order to 
radially compress the collet segments with only low or moderate amounts of 
torque to facilitate a quick and easy change of tools in the collet. 
Ideally, such an improved collet would further have a means for preventing 
errant flows of coolant from entering the space between the tool shank and 
the inner surface of the collet. 
SUMMARY OF THE INVENTION 
Generally speaking, the invention is an endmill adapter of the type having 
an integral collet which includes an improved, torque reducing locknut and 
collet interface, and sealing rings for preventing the entry of errant 
liquids and debris. In the torque reducing interface, one of either the 
inner locknut surface or the outer surfaces of the collet segments 
includes both an engaging portion for wedgingly flexing the collet 
segments inwardly when the locknut is turned, and a non-engaging portion 
in which the collet segments and locknut do not come into contact with one 
another for reducing the binding forces that the applicants have observed 
are largely responsible for the torque required to turn the locknut. The 
non-engaging portion is disposed between the engaging portion and the 
shank mounted ends of the collet segments, and prevents binding from 
occurring between the outer surfaces of the shank mounted ends of the 
collet segments and the inner locknut surface. 
In one embodiment of the invention, the engaging portion is formed on the 
outer surface of the collet segments by a centrally disposed portion that 
is raised with respect to the inner surface of the locknut, and the 
non-engaging portion may be formed by the presence of non-raised, 
frustro-conical surfaces on either side of the centrally raised portion. 
The centrally disposed, raised portion may be a frustro-conical surface 
which is inclined at the same angle as the frustro-conical interior of the 
locknut, while the non-engaging portions may be formed from 
frustro-conical surfaces inclined at an angle greater than and less than 
the inclination of the surface of the locknut. Preferably, the central 
engaging portion of each collet segment is inclined at an angle of 
approximately 4.degree. with respect to the axis of rotation, which is the 
same angle of inclination as the inner surface of the locknut, while the 
non-engaging portions are inclined at angles of 41/2.degree. and 
31/2.degree., respectively. 
In another embodiment of the invention, the outer surface of each of the 
collet segments is arcuate in cross-section such that the middle of the 
arcuate section forms the engaging portion, while the rounded sides of the 
section form non-engaging portions. 
In a third embodiment of the invention, the inner surface of the locknut 
defines the engaging and non-engaging portions, rather than the outer 
surfaces of the collet segments. In this embodiment, while both the inner 
surfaces of the locknut and outer surfaces of the collet segments are 
frustro-conical and inclined at the same angle, the engaging and 
non-engaging portions are defined by a plurality of broad grooves that 
circumscribe the inner diameter of the locknut. The grooves define two 
centrally disposed lands which form the engaging portions of the 
interface, as well as three non-engaging portions, one of which is 
disposed between the lands and the shank mounted ends of the collet 
segments. 
In all three embodiments, the presence of a non-engaging portion in the 
area between the outer surfaces of the shank mounted ends of the collet 
segments and the inner locknut surface advantageously reduces the amount 
of torque needed to turn the locknut into a position that radially 
collapses the collet segments around a tool shank by eliminating 
frictional binding forces which otherwise would occur in this area. 
To further reduce the torque needed to turn the locknut, the invention may 
also include two pairs of grooves that circumscribe both the shank mounted 
ends of the collet segments and the opposite ends of these segments. The 
presence of these grooves reduces the amount of force necessary to 
radially flex the segments inwardly. 
Finally, in order to prevent the entry of errant coolant between the inner 
surfaces of the collet segments and the shank of a tool, a pair of 
circular sealing elements may be seated within grooves present in the 
inner diameter of the collet at either end of the collet segments. The 
grooves in which these annular gaskets are seated may also be the same 
grooves used to lower the amount of force necessary to radially flex the 
collet segments inwardly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference now to Figures i and 2, wherein like numerals designate like 
components throughout all the several figures, the endmill adapter 1 of 
the invention includes a tapered shank 3 on its upper end, and a collet 5 
on its lower end. The tapered shank 3 may be mounted on either the 
rotating spindle of a milling or drilling machine or the non-rotating 
turret of a turning type machine (not shown). A flange 6 separates the 
tapered shank 3 from the collet 5. The upper end of the collet 5 is 
integrally connected to the bottom end of the flange 6. A generally 
tubular locknut 7 circumscribes the outer surface of the collet 5. 
In operation, the shank 9 of a tool such as an endmill is disposed into the 
interior of the collet 5, and the locknut 7 is axially screwed over the 
collet 5 of the adapter 1 in order to radially compress the segments of 
the collet 5 into tight frictional engagement against the tool shank 9. As 
a general guideline, unless specifically stated as tool shank 9, all 
references to shank will be directed toward the tapered shank 3 of the 
endmill adapter. Additionally, while an endmill adapter is discussed 
herein, it should be appreciated that the collet assembly could be applied 
to any toolholder used to secure a tool shank. 
The collet 5 has a frustro-conical, skirt-shaped body 13 having a plurality 
of longitudinal slots 15 uniformly spaced around its exterior. These slots 
15 form resilient collet segments 17 which are radially resilient with 
respect to the axis of rotation of the endmill adapter 1. Screw threads 19 
circumscribe the shank mounted ends of each of the resilient collet 
segments 17 as shown. The opposite ends of the collet segments 17 are 
integrally connected by means of a continuous tie ring 21 formed by 
stopping the slots 15 short of the distal end of the collet body 13. The 
inner surface 23 of the collet has the same cylindrical shape as the tool 
shank 9 which it receives, while its outer surface 25 has a 
frustro-conical profile which is partially complementary in shape to the 
inner surface of the locknut 7 for a purpose that will be described 
presently. 
With specific reference to FIG. 2, the endmill adapter 1 further includes a 
non-pullout wedge 27 that is receivable within a complementarily-shaped 
notch 29 in the endmill shank 9. A wedge aperture 31 is provided through a 
pair of adjacent collet segments 17 for allowing the insertion of the 
wedge 27 through the collet body 13 to contact the tool shank 9. A groove 
33a circumscribes the outer surfaces of the collets at the same latitude 
as the wedge aperture 31. A groove 33b is further provided on the outer 
surface of the wedge aperture 31 which aligns itself with the groove 33a 
in the collet segments 17 when the wedge is inserted through the aperture 
31 and the notch 29 in the tool shank 9. The grooves 33a, b receive an 
elastic O-ring 35 which maintains the wedge 27 in position when the 
locknut 7 is to be reunited with the collet 5 incident to a tool changing 
operation. 
The locknut 7 has a generally tubular body 40 with a generally 
frustro-conical interior 42. The proximal end of the interior 42 includes 
a plurality of screw threads 44 which are engagable with the screw threads 
19 that circumscribe the shank-mounted ends of the collet segments 17. The 
exterior 46 of the locknut 7 is also preferably frustro-conically shaped. 
While the exterior 46 could just as easily be cylindrical in shape, the 
incorporation of a frustro-conical shape to the exterior 46 saves 
materials and reduces the overall weight of the locknut 7. In the 
preferred embodiment, a plurality of indentations 48 are provided around 
the exterior 46 in order to facilitate the firm manual grip of the locknut 
7 by a machine operator. 
The interface between the collet 5 and the locknut 7 in the first 
embodiment of the invention is illustrated in FIG. 3. In the interface of 
this embodiment, each of the collet segments 17 includes a stepped outer 
surface 49 including a proximal angular section 50, a central angular 
section 52 and a distal angular section 54. Each of the angular sections 
50, 52, and 54 have surfaces which are frustro-conical. The surfaces of 
the angular sections 50, 52, and 54 are inclined approximately 
41/2.degree., 4.degree., and 31/2.degree. to the axis of rotation of the 
endmill adapter 1, respectively. The central angular section 52 forms an 
engaging portion 56 between the collet 5 and locknut 7, while the proximal 
and distal angular sections 50 and 54 form proximal and distal 
non-engaging portions 58 and 60 which do not come into contact with the 
frustro-conical interior 42 of the locknut 7. The provision of a proximal 
non-engaging portion 58 between the engaging portion 56 and the proximal, 
shank mounted ends of the collet segments 17 prevents the generation of 
binding forces from occurring in this area which would greatly increase 
the amount of torque necessary to twist the locknut 7 in order to radially 
compress the collet segments 17 into tight engagement around the shank. 
Preferably, the engaging portion 56 of the collet 5 extends across a 
middle portion 52 of each of the collet segments 17 a length of about 20 
to 85% of the length of the entire outer collet surface for all portions 
50, 52, 54. 
An annular clearance recess 62 is provided on the outer surface of the 
distal end of the integral collet 5. This recess 62 fits within an annular 
shoulder 64 located around the inner diameter of the distal end of locknut 
7 when the locknut 7 is axially screwed toward the shank 3 of the adapter 
1. To prevent errant coolant flows and other debris from entering the 
space between the interior surface 42 of the locknut 7 and the stepped 
outer surface 49 of the collet segments 17, an annular sealing ring 66 is 
provided. Ring 66 is seated in an annular groove 68 circumscribing the 
shoulder 64. While the sealing ring 66 does not engage the surface of the 
annular clearance recess 62 when the locknut 7 is in the position 
illustrated in FIG. 3, a sealing engagement between these two components 
is made when the locknut 7 is axially screwed toward the shank 3 to the 
extent necessary to tightly compress the collet segments 17 around the 
shank of a tool. 
The inner diameter of the tie ring 21 of the collet 5 also includes an 
annular groove 72 which not only seats a distal annular sealing ring 74, 
but which further serves, in combination with a circumferential cut 76, to 
define a distal thin section 78 which advantageously renders the collet 
segments 17 more flexible. This same structure is duplicated at the 
proximal end of the collet 5. Specifically, a groove 80 is provided around 
the inner diameter of the proximal, shank mounted ends of the collet 
segments 17. This groove 80 not only seats a proximal annular sealing ring 
81, but also functions in combination with a circumferential cut 82 to 
define a proximal thin section 83 which, like the distal thin section 78, 
renders the collet segments 17 more flexible. The distal and proximal 
annular sealing rings 74 and 81 prevent errant coolant or other debris 
from entering the space between the inner surface 23 of the collet 5 and 
the outer surface of any tool shank disposed therein. Additionally, the 
formation of distal and proximal thin sections 78 and 83 further 
advantageously reduce the amount of torque necessary to turn the locknut 7 
to the axial extent necessary to radially collapse the collet segment 17 
in tight engagement around the tool shank. 
FIG. 4 illustrates the interface between the collet 5 and the locknut 7 in 
the second embodiment of the invention. In the interface of this 
embodiment, each of the collet segments 17 includes a crowned outer 
surface 85 having an arcuate profile. The crowned outer surface 85 
includes a proximal non-engaging portion 87, a central engaging portion 
89, and a distal non-engaging portion 91. As was the case with the first 
described embodiment, the crowned outer surface 85 defines an engaging 
portion 56 which is flanked by a proximal non-engaging portion 58 and a 
distal non-engaging portion 60. The profile of the crowned outer surface 
85 needs only to be curved enough to cause a surface-to-surface, 
venticular-type contact is made between the central engaging portion 89 of 
each of the collet segments 17 and the surface of the interior 42 of the 
locknut 7. 
FIG. 5 illustrates the interface between the collet 5 and a modified 
locknut 95 in the third embodiment of the invention. In this embodiment, 
the engaging and non-engaging portions between the adjacent surfaces of 
the modified locknut 95 and the collet segments 17 are created in the 
inner surface of the locknut 95, instead of the outer surface of each of 
the segments 17. Specifically, proximal, central, and distal 
circumferential grooves 100, 102, and 104 are provided around the inner 
diameter of the locknut 95 in the positions shown. These grooves in turn 
define proximal, central, and distal lands 106, 108, and 110 respectively. 
Preferably, the axial length of the proximal circumferential groove 100 is 
at least at 5% of the axial length of the locknut 95 to prevent the 
previously defined binding forces from occurring between the proximal ends 
of the collet segments 17 and the inner surface of the locknut 95 when it 
is axially screwed toward the shank 3 of the endmill 1. The grooves and 
lands define a proximal non-engaging portion 112, a proximal engaging 113, 
a central non-engaging portion 114, a central engaging portion 115, a 
distal non-engaging portion 116, and a distal engaging portion 117. The 
provision of the engaging and non-engaging portions illustrated in FIG. 5 
has been found by the applicants to substantially reduce the amount of 
torque required to screw the modified locknut 95 into a position which 
firmly radially collapses the collet segment 7 around the shank of an 
endmill or other tool. 
Certain modifications, variations, and additions to the invention will 
become evident to those having skill in the art. All such modifications, 
additions, and variations are intended to be encompassed within the scope 
of this invention, which is limited only by the claims appended hereto.