Cutting by use of rotating axially moving tool – Tool-support – With tool-retaining means
Patent
1988-12-19
1994-11-29
Howell, Daniel W.
Cutting by use of rotating axially moving tool
Tool-support
With tool-retaining means
279 42, 279 467, 279 48, 279155, 408226, B23B 31165, B23B 31173, B23B 5100
Patent
active
053684214
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a tool holder and a tool therefor and is particularly but not exclusively concerned with a tool holder suitable for mounting on a spindle of a milling machine or CNC machinery centre or a tool holder in the form of a chuck e.g. for a drilling machine, machine tool turret, lathe tailstock or portable drill.
Known types of tool holders for use with milling machine and CNC machines are shown partly in cross-section FIGS. 1 and 2 of the accompanying drawings.
In FIG. 1 a body 10 has a taper shank 11 for location in a spindle (not shown) of the machine. The body 10 is formed with a blind bore 12 coaxial with the taper shank 11 and external screw threading 13. The blind end of the bore 12 is provided with a centre 14 and locating depressions 15 for anti-rotations projections 16 on a cylindrical nut 17. The nut is a close sliding fit in the bore 12. The bore 12 houses a sleeve 18 which is a close sliding fit in the bore. The sleeve has an internal tapered surface 19 which engages an external tapered surface 9 on a collet 20. The collet comprises a sleeve formed with slits 21 in known manner extending from the left hand end as shown and which terminate short of the opposite end. A clamping nut or nose cap 22 screws on to the thread 13. This type of tool holder is used to hold a tool 23 having a straight shank 24 and a screw threaded right hand end 25. The end 25 (which has a right hand screw thread) screws into the nut 17 and torque applied to the nose cap 22 urges the surface 9 of collet 20 against surface 19 of the sleeve 18 so that the collet contracts to grip the shank 24. Rotation and axial withdrawal of the tool is resisted by the combined effect of the collet 20 and nut 17. However, if rotational forces on the tool are sufficient to overcome the frictional grip of the collet, and if the rotational direction of the spindle is of opposite hand to that of the threaded section 25, it is possible for the tool to unscrew from the nut 17 and this can prove to be a problem. Another problem which arises is that the tolerance between the sleeve 18 and bore 12 can sometimes be such as to permit a small degree of radial movement of the sleeve in the bore. In certain cases this can lead to `chattering` of the tool, impairing the finish on a workpiece and resulting in inaccuracies.
FIG. 2 shows an alternative type of tool holder where the nut 17 is dispensed with and the threaded section 25 of the shank screws directly into the collet 20. In this case, the nose cap 22 engages the sleeve 18 to contact the collet. It will be appreciated that the problems outlined above are not overcome by the FIG. 2 tool holder.
If the tool should rotate during use as described above it would also shift axially due to the screw thread on the shank 24 and any setting which had been carefully selected by the machine setter beforehand would alter. Such axial shifting would clearly be disadvantageous as it would then be necessary to interrupt production and reset the tool.
One object of the present invention is to provide a tool holder which substantially avoids the foregoing problems.
According to one aspect of the invention there is provided a tool holder for receiving a tool shank having a tapered surface and which comprises a body, shank retaining means on the body and means for causing the shank retaining means to grip the shank, said shank retaining means including shank engaging surface means which, in use, lie substantially on the surface of a notional cone which tapers in the direction of withdrawal of the shank from the tool holder.
According to a further aspect of the invention there is provided a tool holder retaining a tool shank having a tapered surface, the tool holder comprising a body, shank retaining means on the body and means causing the shank retaining means to grip the shank, the tapered surface of the shank tapering towards a working surface of the tool.
Retention of the shank by its tapered surface assists considerably in overcoming the foregoing problems.
The body may be formed with a recess wh
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