Tool Holder

Details Tool Holder Tool Holder

1999-09-23

2001-05-01

Howell, Daniel W. (Department: 3722)

Gear cutting, milling, or planing

Milling

With cutter holder

C279S143000, C408S23900A

Reexamination Certificate

active

06224306

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a tool holder for detachably holding various tools such as drills and end mills.
FIG. 8
shows a conventional tool holder detachably mounted on the spindle of a machining center. It comprises a tool holding portion
40
for detachably holding a tool, a flange
41
keyed to the spindle
1
such that torque is transmitted from the spindle, and a tapered shank
42
adapted to be inserted in a tapered bore
2
formed in the spindle
1
. A pull stud
43
is provided at the tip of the tapered shank
42
.
The tool holder is coupled to the spindle
1
by inserting the tapered shank
42
into the bore
2
of the spindle, gripping the pull stud
43
with a clamp (not shown) housed in the spindle, and pulling it in.
There are two types of tool holders, i.e. a single-face bind type in which only a tapered surface contacts the spindle
1
, and a two-face bind type. The single-face bind type is a type in which the tapered outer surface of the tapered shank
42
is brought into close contact with the inner wall of the tapered bore
2
as shown in FIG.
8
. The two-face bind type is a type in which the end face of the flange
41
is brought into close contact with the end face of the spindle
1
and the tapered outer surface
42
a
of the tapered shank
42
comes into close contact with the tapered inner wall
2
a
of the tapered bore
2
as shown in FIG.
9
.
Tool holders of either type have the following problems. When the spindle
1
begins to rotate at a high speed around 20000 rpm, the diameter of the bore
2
tends to increase under centrifugal force as shown by chain lines a as shown in
FIGS. 8 and 9
. Thus, with the single-face bind type shown in
FIG. 8
, a gap forms between the tapered inner surface
2
a
of the bore
2
and the tapered outer surface
42
a
of the tapered shank
42
. The gap causes the tool holder to be pulled further into the spindle, so that the tip of the tool T held by the tool holder tends to run out and/or displace axially. This makes accurate machining difficult.
With the two-face bind type shown in
FIG. 9
, too, a gap forms between the tapered inner surface
2
a
of the bore
2
and the tapered outer surface
42
a
of the tapered shank
42
, though the tool holder is not pulled into the spindle. This lowers the rigidity of the tool holder, thus making accurate machining impossible.
An object of this invention is to provide a tool holder which can maintain rigidity even if the inner diameter of the shank inserting bore increases when the spindle is revolving at a high speed.
SUMMARY OF THE INVENTION
According to this invention, there is provided a tool holder for detachably supporting a tool. The tool holder comprises a shank adapted to be inserted in a tapered bore formed in a spindle of a machine tool, a flange adapted to abut an end face of the spindle when the shank is pulled into the spindle, and a tool holding portion for detachably supporting a tool. The shank has on an outer periphery thereof a first cylindrical surface formed near its front end and a second cylindrical surface having a larger diameter than the first cylindrical surface at its rear end near the flange. The holder further comprises a tapered sleeve mounted on the shank, a resilient device biasing the tapered sleeve toward the front end of the shank, and a fall-off prevention structure for preventing the tapered sleeve from moving off the front end of the shank. The tapered sleeve is formed with a tapered outer surface adapted to be brought into close contact with the tapered inner surface of the tapered bore formed in the spindle, and an inner surface adapted to be brought into close contact with the second cylindrical surface of the shank. The tapered sleeve is thin enough so as to be resiliently deformable inwardly by coming into contact with the tapered inner surface of the tapered bore of the spindle when moved axially due to bias by the resilient device.
With this arrangement, when the inner diameter of the shank bore of the spindle increases under centrifugal force at high speed so that a gap forms between the tapered inner wall of the spindle bore and the tapered outer surface of the tapered sleeve, the resilient device urges the tapered sleeve to move it axially in a direction to remove the gap and thereby move into close contact with the tapered inner wall of the spindle.
Also, axial movement of the tapered sleeve decreases its inner diameter, so that the tapered sleeve tightly fits on the second cylindrical surface of the shank with interference. This insures that workpieces can be worked with the tool with high precision.
The inner diameter of the tapered sleeve at its small-diameter end should be substantially equal to the diameter of the first cylindrical surface of the shank to maintain the centripetal tendency and rigidity of the tool holder.
The provision of relieved portions at the large-diameter end of the tapered sleeve makes it elastically deformable inwardly when it is moved due to axially bias by the resilient device into contact with the tapered inner wall of the shank receiving bore of the spindle.


REFERENCES:
patent: 3136217 (1964-06-01), Swanson et al.
patent: 3554080 (1971-01-01), Hermann
patent: 4714389 (1987-12-01), Johne
patent: 4840520 (1989-06-01), Pfalzgraf
patent: 4886402 (1989-12-01), Pfalzgraf
patent: 5030047 (1991-07-01), Pfalzgraf
patent: 5716173 (1998-02-01), Matsumoto
patent: 5775857 (1998-07-01), Johne
patent: 5964556 (1999-10-01), Toyomoto
patent: 6077003 (2000-06-01), Laube
patent: 263484 (1989-01-01), None

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