Cutting by use of rotating axially moving tool – Tool or tool with support – Having stepped cutting edges
Reexamination Certificate
2001-03-27
2002-06-18
Howell, Daniel W. (Department: 3722)
Cutting by use of rotating axially moving tool
Tool or tool with support
Having stepped cutting edges
C408S230000, C408S233000, C408S713000
Reexamination Certificate
active
06406226
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority benefits under 35 USC § 119 on the basis of Japanese Patent Application No. 2000-99539, the disclosure thereof being incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a throwaway tip for drilling. The invention further relates to a drill holder for holding such a throwaway tip at a front end thereof.
Drills for drilling a workpiece such as of a metal include: solid type drills which have a unitary drill structure; and throwaway-tipped drills which have a drill holder, and a throwaway tip having a cutting edge and adapted to be removably attached to a front end of the drill holder.
The throwaway-tipped drills are classified into a double tip type and a single tip type.
A throwaway-tipped drill of the double tip type has two tips including an inner cutting tip which has an inner cutting edge for cutting a center area of a hole being drilled, and an outer cutting tip which has an outer cutting edge for cutting a circumference area of the hole, the two tips being attached to a front end of a drill holder (Japanese Laid-Open Patent Publication JP 10-29108A(1998)).
The construction of the double tip type is suitable for a larger-size drill having a greater drilling diameter. However, it is difficult to apply this construction to a smaller-size drill having a drilling diameter of smaller than &phgr;10 for the following reasons.
It is difficult to provide a space sufficient to accommodate the two tips attached to the front end of the holder.
Further, it is difficult to provide a space for smooth ejection of chips generated by cutting a workpiece with the inner cutting edge and the outer cutting edge of the tip.
Since screws for fixing the tips to the holder are very small in size, a sufficient fixing strength cannot be ensured.
Therefore, the smaller-size drill mainly employs the construction of the single tip type.
The throwaway-tipped drill of the single tip type generally employs a tip having a similar tip shape to the conventional solid type drill. More specifically, a tip
91
is employed which has a pair of long cutting ridges
91
b
,
91
b
each extending from a tip point
91
a
positioned on a rotation axis of the drill across the entire radius of a hole being drilled as shown in
FIGS. 8A
to
8
C (Japanese Laid-Open Patent Publication JP 10-328918A(1998)).
However, the cutting ridges
91
b
,
91
b
of the tip
91
each have a great length, so that the tip
91
is subjected to a great cutting resistance during drilling. Therefore, it is necessary to firmly fix the single tip
91
to a front end of a holder
93
with two screws
92
,
92
. Further, the tip
91
needs to have a greater thickness. This makes it difficult to provide a space for ejecting chips from the hole.
The inventor of the present invention previously developed a throwaway tip of the single tip type having a similar front portion shape to that of the throwaway-tipped drill of the double tip type (Japanese Laid-Open Patent Publication JP 11-188518A(1999)). This throwaway tip has an inner cutting edge and an outer cutting edge which are respectively modeled after the inner cutting edge of the inner cutting tip and the outer cutting edge of the outer cutting tip of the throwaway-tipped drill of the double tip type and formed integrally on the single tip.
The inner cutting edge of the throwaway tip is merely required to have a length sufficient to cut a center area of a hole being drilled. Similarly, the outer cutting edge is merely required to have a length sufficient to cut a circumference area of the hole. Therefore, the lengths of the inner cutting edge and the outer cutting edge can be reduced as compared with the cutting ridges of the conventional single tip type drill which each extend across the entire radius of the hole, so that the cutting resistance exerted on the tip during drilling can be reduced. As a result, the thicknesses of the inner cutting edge and the outer cutting edge of the tip can be reduced, and the tip can be fixed to a holder with a single screw. Further, a sufficient space can be provided for ejecting chips from the hole.
The inventor has recently conducted studies on the throwaway tip and the drill holder to be employed in combination with the throwaway tip. As a result, the inventors have found that the constructions described in the aforesaid publications need further improvement in the function thereof, particularly, for smoothly ejecting the chips from the hole.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel throwaway tip which allows for easier chip ejection than the prior art. It is another object of the invention to provide a novel drill holder for a throwaway tip which allows for easier chip ejection than the prior art.
In accordance with an inventive aspect of claim
1
, there is provided a throwaway tip for drilling a hole, which comprises: an inner cutting edge provided at a front end of a drill direction of the tip for cutting a center area of the hole; an outer cutting edge provided at the front end of the tip for cutting a circumference area of the hole; a first rake face provided on one side of the tip; a first bearing face provided on the other side of the tip in a back-to-back relation with the first rake face; a first front flank provided on the front end of the tip as intersecting the first rake face and the first bearing face; the inner cutting edge being defined as a ridge by an intersection between the first rake face and the first front flank and extending as crossing the drilling direction; a second rake face provided on the other side of the tip; a second bearing face provided on the one side of the tip in a back-to-back relation with the second rake face; and a second front flank provided on the front end as intersecting the second rake face and the second bearing face; the outer cutting edge being defined as a ridge by an intersection between the second rake face and the second front flank and extending as crossing the drilling direction; the first rake face being located at a lower level than the second bearing face on one side of the tip, and connected to the second bearing face by a first curved surface for guiding chips generated by cutting with the inner cutting edge.
Conventionally, the inventor has designed a tip so that a greater chip ejection space can be provided on the side of the inner cutting edge than on the side of the outer cutting edge for ejecting chips generated on the side of the inner cutting edge as smoothly as possible. This is because chips generated on the side of the inner cutting edge and on the side of the outer cutting edge are different in shape and, hence, are ejected through different chip ejection mechanisms.
For example, a chip K generated when a portion of a workpiece around the center of a hole being drilled along the rotation axis Pv of a drill is cut with the inner cutting edge
11
is in a three-dimensional helical shape such that cones, of which apex corresponds to a center of the hole, are stacked one on another as shown in FIG.
4
A. This is because a rate at which the workpiece is cut with the inner cutting edge is zero at the center of the hole and increases as a radial distance from the center increases. In order to smoothly eject the chip K of such a complicated three-dimensional shape from the hole, it is necessary to keep the chip continuous with least discontinuity. The continuous chip K without discontinuity gradually grows in a direction indicated by a solid line arrow in the figure as the drilling proceeds, and is automatically and continuously carried away from the hole through a flute of the holder.
On the contrary, a chip generated when a relatively small portion of the workpiece which corresponds to a circumference area of the hole is cut with the outer cutting edge is in the shape of a strip having a given width or segments of the strip. This is because the outer cutting edge does not produce so great a difference in cutting rate between an axial s
Hogan & Hartson L.L.P.
Howell Daniel W.
Kyocera Corporation
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