Title of Invention

CLAMPING APPARATUS FOR FIXING A COLLET TO A CHUCK

Abstract The clamping apparatus (10) comprises a chuck member (1) and a collet member (2) to be clampingly fixed thereto. The collet member (2) comprises, at its rear side, a peripheral shoulder (28). The top side of this shoulder (28) is provided with a thrust surface (29) adapted to engage radially displaceable clamping balls (17) of the chuck member (1). The bottom side of the shoulder (28) is provided with four centering grooves (30a, 30b, 30c, 30d), corresponding in size and location to and cooperating with four centering cams (12a, 12b, 12c. 12d) provided in the chuck member (1). Upon clamping the collet member (2) to the chuck member (1), the collet member (2) is positioned in X- and Y-directions as well as regarding the angular orientation around the Z-axis by means of the centering cams (12a, 12b, 12c, 12d) of the chuck member (1) engaging the centering grooves (30a, 30b, 30c, 30d) of the collet member (2). For defining an exact position of the collet member (2) in Z- direction, the collet member (2) is provided with an annular rear surface (31) adapted to rest on Z- reference surface portions (13a, 13b, 13c, 13d) of the chuck member (1) upon clamping the collet member (2) to the chuck member (1).
Full Text The present invention refers to a clamping apparatus for fixing
a collet member to a chuck member.
With the expression "Collet Member", in the present context, a
slotted clamping sleeve member is understood, having a conical
portion, which is adapted to clamp an object, particularly a work
piece to be machined, by radially forcing out or forcing in the
clamping jaws of the collet member. Such collet members are used,
for instance, with turning lathes where they have a female thread
to be screwed onto a threaded spindle of the lathe.
A fundamental disadvantage of known conventional collet members
consists in the fact that both their angular position around
the rotational axis, i.e. the central longitudinal or Z-axis, as
well as their position in the direction of the extension of the Z-
axis is not or, at least, not exactly defined with regard to the
position of the spindle. In machining axially symmetrical work
pieces in a lathe, the afore mentioned disadvantage is of secondary
importance. However, more and more often the need arises to
clamp work pieces to machine tools other than lathes that are not
axially symmetrical by means of collet members; in this case, the
exact definition of the position of the work piece not only in X-
and Z-direction, but also in Z-direction, i.e. along the extension
of the central longitudinal axis, as well as with regard to their
angular orientation around the Z-axis is highly desirable.
Hitherto, in order to use collet members in a positionally
well defined manner, i.e. both in X- and Y-directions as well as
in Z-direction and regarding the angular orientation around the Z-
axis, intermediate pallet members had to be used to which the collet
member is fixed and which are provided with positioning or
centering elements. That pallet member, then, can be attached to a
corresponding chuck member provided with positioning or centering

elements cooperating with,the elements of the intermediate pallet
member.
The patent publication FR-A-2,694,222 discloses a tool drill
chuck, comprising a tool holding member, preferably in the shape
of a tubular sleeve member, a disc-shaped member that can be connected
to the tool holding member, and a device adapted to be rotated
by a machine to rotate the afore mentioned disc-shaped member.
Thereby, the tool holding member, designed as a hollow rotational
element with a closed end and engaging the disc-shaped member,
comprises two axially aligned portions, one of which serving
for receiving a drill bit and the other one serving for receiving
a tap for cutting a thread in a bore created by the afore mentioned
drill bit. This publication does not disclose an informative
basis for an exact positioning of a work piece in X- and Y-
directions. Neither are any suggestions disclosed for realizing an
exact positioning of the work piece in Z-direction.
It is an object of the present invention to provide a clamping
apparatus for fixing a collet member to a chuck member directly,
easily, quickly and in a well defined position in X-, Y- and Z-di-
rections as well as regarding its angular orientation around the
Z-axis.
This and other objects are met with a clamping apparatus, comprising
a chuck member having clamping means adapted to clampingly
fix a collet member, and a collet member adapted to be fixed to
the chuck member and having first centering means for aligning the
position of the collet member with regard to the chuck member.
The chuck member is provided with second centering means for
aligning the position of the collet member with regard to the
chuck member and cooperating with the first centering means of the
collet member.
The first centering means of the collet member comprises a
plurality of first centering elements located at the rear side of
the collet member facing the chuck member, and the second centering
means of the chuck member comprises a plurality of second centering
elements corresponding to the plurality of first centering

elements of the collet member regarding size and location. The
second centering elements are adapted to engage the first centering
elements of the collet member upon fixing the collet member to
the chuck member to align the collet member with regard to the
chuck member at least in X- and Y-directions.
The collet member is provided with a thrust surface adapted to
be engaged by the clamping means of the chuck member to clampingly
fix the collet member to the chuck member, or the collet member
comprises a clamping stud provided with a thrust surface adapted
to be engaged by the clamping means of the chuck member to clampingly
fix the collet member to the chuck member.
In the following, embodiments of the clamping apparatus according
to the invention will be further described, with reference
to the accompanying drawings, in which:
Fig. 1 shows an exploded view of a clamping apparatus comprising
a chuck member and a collet member;
Fig. 2 shows a perspective bottom view of the collet member;
Fig. 3 shows a partially longitudinally sectioned view of the
chuck member and the collet member attached thereto;
Fig. 4 shows a perspective view of another embodiment of the
clamping apparatus;
Fig. 5 shows a longitudinal sectional view of the clamping apparatus
according to Fig. 4; and
Fig. 6 shows a collet member provided with a clamping stud.
Fig. 1 shows an exploded view of a clamping apparatus 10, comprising
a chuck member 1, a collet member 2 adapted to be clampingly
fixed to the chuck member 1, and an actuating bolt 3. The Z-
axis of the apparatus, simultaneously constituting the longitudinal
central axis, is designated by reference numeral 46. Even if
the actuating bolt 3 is shown in Fig. 1 separately, normally it
constitutes an inherent part of the chuck member 1.
The chuck member 1 is provided with an annular protrusion 11.
On the top front face of the protrusion 11, four centering cams
12a, 12b, 12c and 12d are located. The four centering cams 12a,
12b, 12c and 12d are evenly distributed along the circumference of

the top front face of the protrusion 11. A first Z-axis rest surface
13a is located between the centering cams 12a and 12b, a second
Z-axis rest surface 13b is located between the centering cams
12b and 12c, a third Z-axis rest surface 13c is located between
the centering cams 12c and 12d, and a fourth Z-axis rest surface
13d is located between the centering cams 12d and 12a. All four Z-
axis rest surfaces 13a, 13b, 13c and 13d are somewhat elevated
above the top front face of the protrusion 11. In the center of
the Z-axis rest surface 13b, an indexing pin 14 is provided, towering
above the rest surface 13b.
The protrusion 11 is surrounded by an annular ball retainer
16, adapted to receive a plurality of clamping balls 17 distributed
along an annulus and provided with an external male screw
thread. The clamping balls 17 are received in bores 18 of the ball
retainer 16. Screwed onto the outer male screw thread of the annular
ball retainer 16 is a union nut 19, having an inner conical
thrust surface 20 adapted to radially displace the clamping balls
17. The top of the union nut 19 is provided with a sealing lip 8,
resting against the outside of the ball retainer 16. The ball retainer
is attached to a base plate 21 by means of screws 15. The
base plate 21 itself is provided with fixing means (not shown) to
be attached to a suitably designed retainer means to be provided
on the machine tool to which the clamping apparatus 10 is to be
attached.
The actuating bolt 3 is to be located in the interior of the
chuck member 1 and is axially movable, i.e. in Z-direction along
the axis 46. The displacement of the actuating bolt 3 is performed
preferably pneumatically. The front portion of the actuating bolt
3 is provided with a conical thrust surface 4, adapted to radially
expand the collet member 2, as will be explained in more detail
herein after..
The collet member 2, shown in Fig. 1 in a partially sectioned
view, has essentially a hollow cylindrical shape. The front portion
23 of the collet member 2 is provided with slots 25a, 25b,
dividing the front portion 23 of the collet member 2 into radially

expandable and compressible clamping jaws 24a, 24b, 24c and 24d.
Thus, the collet member 2 of this embodiment comprises a total of
four slots and four clamping jaws. It is understood that the collet
member 2 could be provided with fewer, for example three, or
with more, for example six or eight, clamping jaws. The front portion
23 of the collet member 2 is provided with a central bore 26,
the diameter thereof corresponding to the diameter of the shaft of
the tool to be used with the particular collet member 2.
The back side of the collet member 2 is provided with an annular
shoulder 28, having an annular front face 31 at its bottom.
The annular front face 31 constitutes the Z-axis stop member when
the collet member 2 is attached to the chuck member 1. The top
side of the shoulder 28 is provided with an oblique thrust surface
29. The collet member 2 having been inserted into the chuck member
1, the clamping balls 17 engage the oblique thrust surface 29 to
fix the collet member 2 to the chuck member 1.
The lower front face 31 of the collet member 2 is provided
with centering grooves 30a, 30b, corresponding to the centering
cams 12a, 12b, 12c, 12c as far as position and shape is concerned,
and serving for positioning the collet member 2 with regard to the
chuck member 1 both in X- and in Y-direction as well as regarding
the angular position around the Z-axis. It is to be noted that the
collet member 2 is provided with a total of four centering grooves
30; however, in the illustration of Fig. 1, only two of them, i.e.
the grooves 30a and 30b are visible. Moreover, the annular front
face 31 of the collet member 2 is provided with a indexing aperture,
also not visible in Fig. 1, adapted to receive the indexing
pin 14 provided on the chuck member 1. A shaft portion 32 constitutes
the central portion of the collet member 2 and connects the
front portion 23 of the collet member 2 with the shoulder 28.
The front portion 23 of the collet member 2 is provided with a
conically narrowing recess 34 located at its back side. This recess
34 extends within the shaft portion 32 from the back side of
the front portion 23 of the collet member 2 to the bore 26. The
recess 34 is delimited by protruding, conically widening wall por-

tions 35a, 35b. The wall portions 35a and 35b are subdivided by
the slots 25a, 25b in the front portion 23 of the collet member 2.
Thus, a total of four wall portions are present, separated from
each other by the afore mentioned slots 25a, 25b. As soon as the
actuating bolt 3 is pushed into the recess 34, the clamp jaws 24a,
24b, 24c (and also the forth clamp jaw not shown in Fig. 1) are
radially forced apart.
It is understood that the configuration of the centering
grooves and centering cams could be inverted, in other words, the
centering cams could be provided on the collet member 2 and the
centering grooves on the chuck member 1.
Fig. 2 shows a perspective view of the collet member 2 from
the bottom. In this illustration, it is particularly shown that
the four centering grooves 30a, 30b, 30c, 30d are machined into
that front surface 31 of the shoulder 28 that is remote from the
front portion 23 of the collet member 2, and that the shoulder 28
is provided with a thrust surface 29 adapted to engage the clamping
balls 17 of the chuck member 1. Moreover, the indexing aperture
33 adapted to receive the indexing pin 14 is clearly visible,
the cooperation of the indexing pin 14 and the indexing aperture
33 permitting an approximate definition of the position of the
collet member 2 around the Z-axis and ensuring a correct attachment
of the collet member 2 to the chuck member 1 as far as the
approximate angular position around the Z-axis is concerned.
The annular surface portions of the rear front face 31 of the
collet member 2, located between the centering grooves 30a, 30b,
30c, 30d, constitute the Z-reference surface of the collet member
2 upon clamping the collet member 2 to the chuck member 1. Due to
the fact that the centering grooves 30a, 30b, 30c, 30d are machined
into the shoulder 28 of the collet member 2 in the region
of the thrust surface 29, as seen in axial direction, and also due
to the fact that the collet member 2 is fixed in Z-direction at
this thrust surface 29 by means of a plurality of clamping balls
17 arranged along an annulus, the collet member 2 can be fixed to
the chuck member 1 in a very well defined position regarding all

three axes and the angular orientation, and it can accept very
high forces, particularly also in radial direction.
Fig. 3 shows a partially longitudinally sectioned view of the
chuck member 1 and the collet member 2 attached thereto. The collet
member 2 is fixed to the chuck member 1 by means of the clamping
balls 17 engaging the thrust surface 29 provided on the shoulder
28. The clamping balls 17 are pressed radially inwards by the
thrust surface 20 of the union nut 19, the latter one having been
manually rotated into its operating position as shown on Fig. 3.
Due to the fact that the clamping balls 17 are pushed against the
thrust surface 29 of the shoulder 28 of the collet member 2, the
collet member 2 is pressed against the chuck member 1 in Z-direction.
The actuating bolt 3 provided for radially forcing apart the
clamping jaws 24 of the collet member 2 is shown in Fig. 3 in its
upper operating position. When the actuating bolt 3 is pushed upwards,
its conical thrust surface 4 engages the wall portion of
the recess 34 and the conically widening wall portions 35a, 25b,
respectively,, with the result that the clamping jaws 24a, 24b, 24c
(and also 24d, not shown in Fig. 3) of the collet member 2 are
forced apart in radial direction.
Such a clamping apparatus 10 is particularly suitable for fixing
work pieces or tools that are attached to the collet member 2
by radially forcing apart the clamping jaws thereof. The hollow
work piece to be attached to the collet member 2 (not shown) is
pushed over the collet member 2 such that it is fixed along the
circumference of the collet member 2 by radially forcing the
clamping jaws apart. Thereby, the outline of the collet member 2
is preferably adapted to match the inner contour of a recess in
the work piece to be fixed to the chuck member 1. Another possibility
is to provide an adapter that can be attached to the work
piece and that has a hollow portion matching the outline of the
collet member 2; it is also possible to match the work piece itself
to the outline of the collet member 2.
As long as the actuating bolt 3 is pushed into the recess 34
of the collet member 2, the work piece is fixed to the collet mem-

ber 2. The actuating bolt 3 having been pulled back, the work
piece can be removed from the collet member 2, because the clamping
jaws 24 resiliently return into their unloaded initial position.
Basically, it is true that the four centering cams 12a, 12b,
12c, 12d of the chuck member 1 enter the four centering grooves
30a, 30b, 30c, 30d of the collet member 2 upon attaching the collet
member 2 to the chuck member 1. Thereby, the collet member 2
is positioned with regard to the chuck member 1 in X- and Y-directions
as well as regarding its angular orientation around the Z-
axis. The centering grooves 30a, 30b, 30c, 30d of the collet member
2 are dimensioned and adapted to the size of the centering
cams 12a, 12b, 12c, 12d of the chuck member 1 such that the centering
cams 12a, 12b, 12c, 12d of the chuck member 1 enter the
centering grooves 30a, 30b, 30c, 30d of the collet member 2 that
far, the collet member 2 being loosely put onto the chuck member
1, that a gap with a width in the range of 0.01 to 0.1 mm remains
between the Z-axis rest surfaces 13a, 13b, 13c, 13d of the chuck
member 1 and the annular front face 31 of the collet member 2. Upon
tightening the union nut 19, this gap disappears since the centering
cams 12a, 12b, 12c, 12d of the chuck member 1 enter the
centering grooves 30a, 30b, 30c, 30d of the collet member 2 deeper,
i.e. by the amount of the width of the former gap. Thereby,
advantage is taken of the inherent elasticity of the material,
usually steel, insofar as the centering grooves 30a, 30b, 30c, 30d
of the collet member 2 are somewhat widened. Such deformation occurs
within the region of the elasticity of the material; the result
is that centering elements can be avoided that are resiliently
elastic in Z-direction. The union nut 19 having been tightened,
the collet member 2 rests with its annular front face 31 on the
rest surfaces 13a, 13b, 13c, 13d serving as Z-axis reference surfaces;
thus, the position of the collet member 2 with regard to
the chuck member 1 is exactly defined in Z-direction, too.
Fig. 4 shows a perspective view of another embodiment of the
clamping apparatus. The collet member 2a is provided with an oval

recess 37 for fixing a corresponding work piece 39. The bottom 38
of the recess 37 constitutes the Z-reference surface for the work
piece 39. In this case, the work piece 37 is not fixed to the collet
member 2a by radially forcing out the clamping jaws thereof,
but by radially forcing in the latter ones. Such radial forcing in
of the clamping jaws is effected by an actuating bolt 3a having a
different design, as will be further explained herein after with
reference to Fig. 5.
Fiq. 5 shows a longitudinal sectional view of the clamping apparatus
according to Fig. 4. Clearly visible is the actuating bolt
3a. Instead of a conical thrust surface, the actuating bolt 3a is
provided with a recess 36, the inside shape of which substantially
corresponding to the outline of the wall portions 35a, 35b delimiting
the recess 34 in the collet member 2a The inside of the recess
36 of the actuating bolt 3a engages the outside of the conical
wall portions 35a, 35b when the actuating bolt 3a is pushed
upwards, with the result that the clamping jaws are forced inwards,
thus clamping the work piece 39 in the collet member 2a.
Fig. 6 shows another embodiment of a collet member 2. The collet
member 2 is provided with a clamping stud 41, serving for
pulling in and fixing the collet member 2 to the chuck member 1.
The lower end of the clamping stud 41 is provided with a peripheral
shoulder 42, having a beveled thrust surface 43 that can be engaged
by the clamping balls 17 of the chuck member 1. It is understood
that the chuck member 1 has to match a collet member 2 provided
with a clamping bolt 41. Particularly, the clamping balls 17
of the chuck member 1 have to be located further downwards.
Preferably, the clamping bolt 41 is of hollow cylindrical shape;
thereby it is possible to provide an actuating bolt extending
through the clamping bolt 41 and serving for forcing apart or
forcing in the clamping jaws.
A collet member 2 designed along the lines of the present invention
can be fixed to a chuck member 1 directly, simply, quickly
and in a well defined position.

The provision of a union nut 19 that has to be manually
screwed on to fix the collet member 2 has the advantage that the
clamping apparatus 10 is of a very compact design and can be manufactured
in a cost effective manner. Instead of a manually applicable
union nut for fixing the collet member, the chuck member 1
could be provided with a spring-loaded, pneumatically or hydraulically
displaceable clamping piston whose inside comprises a conically
narrowing thrust surface for radially displacing the clamping
balls. If a collet member without a clamping bolt is used, the
entire clamping apparatus can be designed in a very compact manner .

WE CLAIM :
1. A clamping apparatus for fixing a collet to a chuck, comprising a chuck member having
clamping means adapted to clampingly fix a collet member, and a collet member adapted to be fixed
to said chuck member and having first centering means for aligning the position of said collet
member with regard to said chuck member, characterized in that said chuck member has second
centering means for aligning the position of said collet member with regard to said chuck member
and cooperating with said first centering means of said collet member, whereby said first centering
means of said collet member comprises a plurality of first centering elements located at the rear side
of said collet member facing said chuck member, whereby said second centering means of said chuck
member comprises a plurality of second centering elements corresponding to said plurality of first
centering elements of said collet member regarding size and location and adapted to engage said first
centering elements of said collet member upon fixing said collet member to said chuck member to
align said collet member with regard to said chuck member at least in X- and Y-directions; and
whereby said collet member or a clamping stud fixed to said collet member is provided with a thrust
surface adapted to be engaged by said clamping means of said chuck member to clampingly fix said
collet member to said chuck member.
2. A clamping apparatus as claimed in claim 1, wherein said collet member is provided with a
peripheral shoulder incorporating said plurality of first centering elements.
3. A clamping apparatus as claimed in claim 1, wherein said thrust surface is provided on said
peripheral shoulder of said collet member.

4. A clamping apparatus as claimed in claim 1, wherein said thrust surface is provided on said
clamping stud of said collet member.
5. A clamping apparatus as claimed in claims 1 and 2, wherein said first centering elements are
located on the back surface of said peripheral shoulder remote from the front portion of said collet
member, whereby the surface areas of said back surface between said first centering elements are
adapted to constitute Z-reference surface portions to define the Z-position of said collet member
when said collet member is fixed to said chuck member.
6. A clamping apparatus as claimed in claim 5, wherein said first centering elements comprise at
least three centering grooves arranged along an annulus and evenly distributed along said annulus for
positioning said collet member with regard to said chuck member in X- and Y-directions as well as
regarding its angular orientation.
7. A clamping apparatus as claimed in claim 5, wherein said first centering elements comprise at
least three centering cams arranged along an annulus and evenly distributed along said annulus for
positioning said collet member with regard to said chuck member in X- and Y-directions as well as
regarding its angular orientation.
8. A clamping apparatus as claimed in claim 1, wherein said chuck member comprises at least
three of said second centering elements corresponding to said first centering elements of said collet
member regarding size and location, said chuck member having a clamping means provided with a
plurality of clamping balls for clampingly fixing said collet member to said chuck member.

9. A clamping apparatus as claimed in claim 8, wherein said clamping means has a union nut,
the inside thereof having a conically narrowing thrust surface adapted to radially displace said
clamping balls upon tightening said union nut.
10. A clamping apparatus as claimed in claim 1, wherein the rear side of a front portion of said
collet member is provided with a conically narrowing recess, subdivided by radially extending slots,
whereby an actuating bolt, provided on said chuck member, is adapted to be pushed into said
conically narrowing recess of said front portion of said collet member to radially expand said collet
member.
11. A clamping apparatus as claimed in claim 1, wherein the tear side of a front portion of said
collet member is provided with a recess delimited by protruding, conically widening wall portions
and subdivided by radially extending slots, whereby an actuating bolt, provided on said chuck
member and having a recess in its front face, is adapted to be pushed over said conically widening
wall portions of said front portion of said collet member to radially contract said collet member.
12. A clamping apparatus as claimed in claim 1, wherein said collet member is provided with an
indexing bore for determining its approximate angular orientation around the Z-axis upon inserting it
into said chuck member.

The clamping apparatus (10) comprises a chuck member (1) and a collet member (2) to be
clampingly fixed thereto. The collet member (2) comprises, at its rear side, a peripheral shoulder
(28). The top side of this shoulder (28) is provided with a thrust surface (29) adapted to engage
radially displaceable clamping balls (17) of the chuck member (1). The bottom side of the shoulder
(28) is provided with four centering grooves (30a, 30b, 30c, 30d), corresponding in size and location
to and cooperating with four centering cams (12a, 12b, 12c. 12d) provided in the chuck member (1).
Upon clamping the collet member (2) to the chuck member (1), the collet member (2) is positioned in
X- and Y-directions as well as regarding the angular orientation around the Z-axis by means of the
centering cams (12a, 12b, 12c, 12d) of the chuck member (1) engaging the centering grooves (30a,
30b, 30c, 30d) of the collet member (2). For defining an exact position of the collet member (2) in Z-
direction, the collet member (2) is provided with an annular rear surface (31) adapted to rest on Z-
reference surface portions (13a, 13b, 13c, 13d) of the chuck member (1) upon clamping the collet
member (2) to the chuck member (1).

Documents:

344-kol-2005-granted-abstract.pdf

344-kol-2005-granted-assignment.pdf

344-kol-2005-granted-claims.pdf

344-kol-2005-granted-correspondence.pdf

344-kol-2005-granted-description (complete).pdf

344-kol-2005-granted-drawings.pdf

344-kol-2005-granted-examination report.pdf

344-kol-2005-granted-form 1.pdf

344-kol-2005-granted-form 18.pdf

344-kol-2005-granted-form 2.pdf

344-kol-2005-granted-form 3.pdf

344-kol-2005-granted-form 5.pdf

344-kol-2005-granted-gpa.pdf

344-kol-2005-granted-priority document.pdf

344-kol-2005-granted-reply to examination report.pdf

344-kol-2005-granted-specification.pdf

344-kol-2005-granted-translated copy of priority document.pdf


Patent Number 225974
Indian Patent Application Number 344/KOL/2005
PG Journal Number 49/2008
Publication Date 05-Dec-2008
Grant Date 03-Dec-2008
Date of Filing 21-Apr-2005
Name of Patentee EROWA AG
Applicant Address WINKELSTRASSE 8, CH-5734 REINACH
Inventors:
# Inventor's Name Inventor's Address
1 KRAMER DIETMAR BIRCHWISSTRASSE 31, CH-8114 DAENIKON
PCT International Classification Number B23B 31/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 00786/04 2004-05-04 Switzerland