Chucks or sockets – Socket type – Side detent
Reexamination Certificate
1999-12-10
2001-10-09
Bishop, Steven C. (Department: 3722)
Chucks or sockets
Socket type
Side detent
C403S362000, C407S040000, C408S233000, C408S713000
Reexamination Certificate
active
06299180
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a clamping mechanism in general and to the clamping of cutting heads to tool holder adaptors in particular.
BACKGROUND OF THE INVENTION
An example of a clamping mechanism employing retaining screws for clamping a cutting head to a tool holder adaptor is described in U.S. Pat. No. 4,575,292 and is shown in FIG.
1
. When this type of clamping mechanism is used in cutting tools having relatively small diameters a certain problem arises that is negligible or does not arise at all, for large diameter cutting tools. This problem entails the distortion of portions of the cutting tool body as a result of radial forces that exist between the retaining screws and the cutting tool body and the fact that for small diameters the body of the tool will distort under the influence of these radial forces.
FIG. 1
will be used as a reference to illustrate the distortion problem, which will be described with reference to
FIGS. 2
to
5
that show various sectional views of the tool shown in FIG.
1
. However, not all the features of the cutting tool shown in
FIG. 1
are relevant to understanding the problem at hand. Therefore,
FIGS. 2
to
5
are only illustrative sectional views of
FIG. 1
showing only relevant features. Furthermore, for illustrative purposes some of the spaces between various parts and the distortions thereof have been exaggerated.
FIG. 1
shows a cutting tool assembly comprising a cutting head
2
clamped to an adaptor
1
. The cutting head has a cutting insert
30
mounted at its front end, and is provided with a shank
5
at its rear end. The adaptor has a bore
3
at its front end in which the shank
5
is co-axially mounted.
The periphery of the adaptor is provided with a threaded through bore
8
a
(This numeral has been added. The rest of the numerals in
FIGS. 1
to
5
are as in the '292 patent.). The shank
5
is provided with a conical bore
7
capable of receiving therein a retaining screw
8
which is screwingly engaged into the threaded bore
8
a
. When mounting the cutting head on the adaptor, the shank
5
of the cutting head is inserted into the bore
3
of the adaptor until the cutting head abutting surface
6
abuts against the adaptor abutting surface
4
. The retaining screw
8
is now screwed into the threaded bore
8
a
in order to clamp the cutting head
2
to the adaptor
1
. The clamping of the cutting head can be considered as a two step process. In the first step the retaining screw is fully screwed into the threaded bore, enters the conical bore
7
, but is not firmly tightened. The screw's conical turned end
9
abuts against the conical bore
7
thereby pushing the shank
5
away from the threaded bore
8
a
towards the adaptor inner wall remote from the threaded bore and at the same time pushing the shank rearwardly relative to the adaptor
1
. At this stage the cutting head cannot be released from the adaptor, but it is not securely clamped in position. In the second step the retaining screw is firmly tightened (see FIG.
2
), ensuring that the axial component Fa of the retaining force F forces the cutting head
2
rearwardly relative to the adaptor
1
whereby the firm abutting of the cutting head abutting surface
6
against the adaptor abutting surface
4
is obtained.
Such a clamping mechanism has a disadvantage that limits the use of the cutting tool assembly in some milling operations due to instability and inaccuracy problems, as will be described below.
FIG. 3
is a cross-sectional view of a cutting tool assembly similar to that shown in
FIG. 2
taken in a plane perpendicular to the axis
10
of the adaptor
11
in the region of contact between the conical end
9
of the screw and the conical bore
7
.
As can be seen in
FIG. 3
, prior to forcibly screwing the retaining screw
18
, there is a gap between the shank
25
and the adaptor
11
. This gap, of dimension h
1
, is due to the difference between the outer diameter d
1
of the cutting head shank and the inner diameter d
2
of the adaptor. This gap which, for illustrational purposes, is shown to be uniform all around the adaptor bore is the required clearance which is essential for the free insertion of the cutting head shank into the adaptor bore. The required clearance is typically in the order of magnitude of 0.02 mm.
FIGS. 4 and 5
show the result of fastening the retaining screw by means of the action of the radial component Fr of the retaining force F, as a two step process. In the first step, as shown in
FIG. 4
, the retaining screw
18
radially pushes the cutting head shank
25
away from the screw through bore
18
a
towards the adaptor inner wall
26
remote from the bore
18
a
. When the shank
25
touches the wall
26
, the distance between the through bore
18
a
and the shank
25
becomes h
2
, which is twice the initial distance h
1
between the shank
25
and the adaptor bore
23
. In the second step, as shown in
FIG. 5
, in order to ensure firm abutting of the cutting head shank
25
against the inner wall
26
and, also, to ensure self-locking of the retaining screw
18
, the screw must be forcibly additionally screwed. The greater the radial component Fr of the retaining force F the greater the reaction force Rf acting on the screw in the opposite direction to the force Fr.
FIG. 5
shows the assembly of
FIG. 4
after the retaining screw
18
was forcibly additionally screwed. As can be seen, the forced screwing distorts the adaptor
11
, in the screw's axial direction, to a distance h
3
between the cutting head shank
25
and the through bore
18
a
. The distance h
3
is greater than the distance h
2
. This means, in practice, that the shank is not best supported in the adaptor bore, and the shank
25
and the adaptor
11
are not co-axial, which, of course, leads to inaccuracy and instability of the cutting tool assembly.
The disadvantages of the clamping mechanism described above are more pronounced in small diameter adaptors where the thickness of the adaptor wall t
1
is relatively small. Clearly, the thinner the adaptor wall the greater the distortion for a given tightening force of the retaining screw. In order to overcome this disadvantage the wall thickness can be increased, but, this may give rise to other difficulties when performing deep pocketing applications because the adaptor external diameter may become larger than the cutting head diameter, a fact that limits the use of the cutting head to depths less than its length.
Another example of a clamping mechanism employing retaining screws for clamping a cutting head to a tool holder adaptor is described in U.S. Pat. No. 4,511,294.
FIG. 6
is a cross-sectional view similar to
FIG. 5
in '294. The reference numerals used herein are compatible with the reference numerals used in '294 with 100 added to them.
As shown in
FIG. 6
, a stub
110
of a shank
103
is inserted into the legs
108
of an adaptor
104
. The stub having radially extending threaded bores
113
. The legs having radially extending holes
111
. The axes of the threaded bores
113
and the holes
111
are parallel and offset relative to one another. When screws
119
having conical heads are inserted into the holes
111
and fully screwed into the threaded bores
113
they urge the rear edge face
114
of the legs
108
against the respective surface
115
of the shank's shoulder
116
. As can be seen, firm abutting is obtained by the axial relative movement between the shank
103
and the adaptor
104
whereby the rear end portions of the legs
108
are wedged into the spaces which are inwardly adjacent to the respective surfaces
115
of the shank's shoulder
116
thus preventing the legs
108
from moving away from each other. In accordance with '294 firm abutting between the adaptor
104
and the shank
103
is not obtained solely by the radial tightening of the screws
119
but also requires the wedging of the rear end portions of the legs
108
against the respective shank's shoulder
116
. The latter being obtained
Petrilin Andrei
Satran Amir
Bishop Steven C.
Iscar Ltd.
Pennie & Edmonds LLP
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