Patent Description:
Conventionally, there is a known core cutter that includes a cylindrical body and a tipped bit. The tipped bit is disposed in a manner to protrude from the distal end of the body. The core cutter is configured to cut a workpiece with the bit when the body is rotated about a rotational axis that is the axis of the body. One of such core cutters is, for example, a hole cutter proposed by <CIT>, which is intended for cutting wooden materials.

The hole cutter for wooden materials, which is disclosed by <CIT>, includes a cylindrical body and a plurality of bits. The plurality of bits are formed on an opening edge at the distal end of the body. The body is provided with notches that are formed corresponding to the plurality of bits, respectively. The notches are intended for discharging swarf that is generated during the cutting.

In the case of <CIT>, and other conventional core cutters, generally speaking, in order to discharge the swarf generated during the cutting, the notches are formed adjacently to the bits at the distal end of the cylindrical body. However, the conventional core cutters have a problem in that when cutting a workpiece having irregularities, the notches bite into the irregularities. <CIT> discloses a bit with a number of diamond tips spaced apart from each other with a clearance.

<CIT> discloses a method for using a core cutter with the features of the preamble of claim <NUM>.

In view of the above, an object of the present invention is to provide a core cutter that is capable of, even in the case of cutting a workpiece having irregularities, preventing the biting into the irregularities more assuredly and to realize, in a balanced manner, both preventing the biting into the irregularities and sufficiently discharging the swarf, and to provide a cutting method using the core cutter.

The present invention solves this problem with a hole cutter having the features of claim <NUM> and a cutting method with the features of claim <NUM>. A core cutter according to the present invention includes: a cylindrical body; and a tipped bit that is disposed in a manner to protrude from a distal end of the body. The core cutter is configured to cut a workpiece with the bit when the body is rotated about a rotational axis that is an axis of the body. At a distal end of the body, a notch is formed adjacently to the bit at a position forward of the bit in a rotation direction of the body. A width of the notch in a circumferential direction of the body at the distal end of the body is less than or equal to <NUM>.

According to the above configuration, the width of the notch, which is formed in the body for the purpose of discharging swarf, is less than or equal to <NUM> in the circumferential direction at the distal end of the body. Thus, the width of the notch is sufficiently smaller than an expected thickness of a rising portion of irregularities of a workpiece. This consequently makes it possible to provide the core cutter, which is capable of preventing, even in the case of cutting a workpiece having irregularities, the notch from biting into the irregularities.

A rake angle of the bit may be a negative angle.

The above configuration improves the strength of the bit.

The width may be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>.

The above configuration makes it possible to realize, in a balanced manner, both preventing the biting into the irregularities and sufficiently discharging the swarf.

The above configuration makes it possible to realize, in a more balanced manner, both preventing the biting into the irregularities and sufficiently discharging the swarf.

The core cutter may include a plurality of the bits. The notch may be formed for each of the bits.

According to the above configuration, the workpiece is cut by the plurality of the bits. This makes it possible to reduce the load on each of the bits, and thereby damage to each of the bits can be further suppressed.

The bits may include a first bit and a second bit. A first distance between a distal end of the first bit and the axis of the body, and a second distance between a distal end of the second bit and the axis of the body, may be different from each other. The first and second bits may be arranged alternately in the circumferential direction of the body.

According to the above configuration, the workpiece can be properly cut by an amount corresponding to the thickness of the bits. Therefore, while cutting the workpiece, the bits and the body can smoothly move forward in the thickness direction of the workpiece.

The bit may include: a protruding portion that protrudes from the distal end of the body; and a fixed portion fixed to the body, the fixed portion being provided such that a position of the fixed portion is shifted from the distal end of the body toward a proximal end of the body. Entirely from a distal end of the notch to a proximal end of the notch, the width of the notch in the circumferential direction of the body may be less than or equal to <NUM>, and the proximal end of the notch may be positioned closer to the distal end of the body than a proximal end of the fixed portion of the bit.

The above configuration makes it possible to more assuredly prevent the biting into the irregularities.

According to the invention, the bit includes:
a protruding portion that protrudes from the distal end of the body; and a fixed portion fixed to the body, the fixed portion being provided such that a position of the fixed portion is shifted from the distal end of the body toward a proximal end of the body. The notch includes:
a distal end portion; and a main portion continuous with a proximal end of the distal end portion. A width of the distal end portion in the circumferential direction of the body is less than or equal to <NUM>. A proximal end of the main portion is positioned closer to the proximal end of the body than a proximal end of the fixed portion of the bit.

In order to solve the above-described problems, a cutting method according to one aspect of the present invention is a cutting method using any of the above-described core cutters. The cutting method includes: a first step of preparing the core cutter, an electric drill to which the core cutter is to be mounted as a distal end tool, and a workpiece having irregularities on a surface thereof; a second step of mounting the core cutter to the electric drill after the first step; and a third step of pressing a distal end side of the core cutter against a rising portion of the irregularities along a rising direction of the rising portion while rotating the core cutter by the electric drill about a rotational axis that is an axis of the core cutter to cut a part of the irregularities after the first and second steps.

According to the above configuration, by using any of the above-described core cutters, the cutting method according to the one aspect of the present invention is able to, even in the case of cutting a workpiece having irregularities, prevent the notch from biting into the irregularities.

The workpiece prepared in the first step may include at least two projections on the surface thereof. The first step may further include preparing a jig, the jig including: a base portion that is placeable on the workpiece such that a bottom surface of the base portion is in contact with upper ends of the respective at least two projections; a cylindrical portion provided upright at a center of an upper end of the base portion; and a through-hole drilled in the jig from the bottom surface of the base portion to an upper end of the cylindrical portion, the through-hole corresponding to an external diameter of the body of the core cutter. The third step may include: placing the jig on the workpiece such that the through-hole of the jig on the bottom surface side of the base portion is positioned between the at least two projections, and such that the bottom surface of the base portion is in contact with the upper ends of the respective at least two projections; and then inserting the core cutter into the through-hole of the jig placed on the workpiece from an upper end side of the jig while rotating the core cutter by the electric drill about the rotational axis, which is the axis of the core cutter, to cut a part of the at least two projections.

According to the above configuration, movement of the core cutter in the radial direction is restricted by the jig, and thereby oscillation of the core cutter can be prevented when cutting the irregularities of the workpiece. Consequently, even in a case where the workpiece has irregularities, the workpiece can be cut as desired.

The third step may include fixing parts of the base portion of the jig, the parts being placed on the upper ends of the respective at least two projections of the workpiece, to the upper ends of the respective at least two projections, and then inserting the core cutter into the through-hole of the jig from the upper end side of the jig.

According to the above configuration, even in a case where the workpiece has irregularities, the workpiece can be cut as desired more assuredly.

For example, the third step may include fixing the parts of the base portion of the jig, the parts being placed on the upper ends of the respective at least two projections of the workpiece, to the upper ends of the respective at least two projections by stepping on the parts by feet, and then inserting the core cutter into the through-hole of the jig from the upper end side of the jig.

For example, the third step may include fixing the parts of the base portion of the jig, the parts being placed on the upper ends of the respective at least two projections of the workpiece, to the upper ends of the respective at least two projections by using fixing members, and then inserting the core cutter into the through-hole of the jig from the upper end side of the jig.

In order to solve the above-described problems, a cutting method with the features of claim <NUM> according to another aspect of the present invention includes: a first step of preparing a core cutter including a cylindrical body and a tipped bit that is disposed in a manner to protrude from a distal end of the body, the core cutter being configured to cut a workpiece with the bit when the body is rotated about a rotational axis that is an axis of the body, an electric drill to which the core cutter is to be mounted as a distal end tool, a workpiece having at least two projections on a surface thereof, and a jig including a base portion, a cylindrical portion, and a through-hole, the base portion being placeable on the workpiece such that a bottom surface of the base portion is in contact with upper ends of the respective at least two projections, the cylindrical portion being provided upright at a center of an upper end of the base portion, the through-hole being drilled in the jig from the bottom surface of the base portion to an upper end of the cylindrical portion, the through-hole corresponding to an external diameter of the body of the core cutter; a second step of mounting the core cutter to the electric drill after the first step; and a third step of, after the first and second steps, placing the jig on the workpiece such that the through-hole of the jig on the bottom surface side of the base portion is positioned between the at least two projections of the workpiece, and such that the bottom surface of the base portion is in contact with the upper ends of the respective at least two projections, fixing parts of the base portion of the jig, the parts being placed on the upper ends of the respective at least two projections, to the upper ends of the respective at least two projections by stepping on the parts by feet, and then inserting the core cutter into the through-hole of the jig placed on the workpiece from an upper end side of the jig while rotating the core cutter by the electric drill about a rotational axis that is an axis of the core cutter, and pressing a distal end side of the core cutter against a rising portion of the at least two projections along a rising direction of the rising portion to cut a part of the at least two projections.

According to the above configuration, movement of the core cutter in the radial direction is restricted by the jig, and thereby the cutting method according to the other aspect of the present invention can prevent oscillation of the core cutter when cutting the irregularities of the workpiece. In addition, the jig is fixed to the workpiece by stepping on the jig with feet. Therefore, the jig will not move when cutting the irregularities of the workpiece. Consequently, even in a case where the workpiece has irregularities, the workpiece can be cut as desired.

The present invention makes it possible to provide a core cutter that is capable of, even in the case of cutting a workpiece having irregularities, preventing biting into the irregularities, and to provide a cutting method using the core cutter.

Hereinafter, a core cutter according to one embodiment of the present invention is described with reference to the drawings. It should be noted that the present invention is not limited to the present embodiment. In the drawings, the same or corresponding elements are denoted by the same reference signs, and repeating the same descriptions is avoided below.

<FIG> show the core cutter according to the one embodiment of the present invention. <FIG> is a front view, and <FIG> is a bottom view. As shown in <FIG>, the core cutter <NUM> according to the present embodiment includes a cylindrical body <NUM> and tipped bits <NUM>. The tipped bits <NUM> are disposed in a manner to protrude from the distal end of the body <NUM>. The core cutter <NUM> is configured to cut a workpiece with the bits <NUM> when the body <NUM> is rotated about a rotational axis that is an axis AX of the body <NUM>.

It should be noted that, in the description below, a direction connecting between the distal end (the lower end in <FIG>) and the proximal end (the upper end in <FIG>) of the core cutter <NUM> may be referred to as a height direction. Also, the distal-end side of the core cutter <NUM> may be referred to as a lower side or downward, and the proximal-end side of the core cutter <NUM> may be referred to as an upper side or upward.

The cylindrical body <NUM> has a proximal end surface and a distal end surface that are both open. That is, the body <NUM> is formed as a hollow body. The body <NUM> includes a body main part <NUM> and a proximal end portion <NUM>. The proximal end portion <NUM> is continuous with the proximal end surface of the body main part <NUM>, and the diameter of the proximal end portion <NUM> is less than that of the body main part <NUM>. The thickness of the distal end portion of the body main part <NUM> (i.e., the dimension of the distal end portion in the radial direction of the body <NUM>) is greater than the thickness of the remaining portion of the body main part <NUM>. The bits <NUM> are fixed to the distal end portion of the body main part <NUM>. It should be noted that the diameter of the body main part <NUM> may be about <NUM>.

The core cutter <NUM> includes a plurality of bits <NUM>. Specifically, the bits <NUM> include five first bits 30a and five second bits 30b. The first and second bits 30a and 30b are arranged alternately in the circumferential direction of the body <NUM>.

<FIG> are enlarged views showing a first bit of the present embodiment. <FIG> is a front view of the first bit, and <FIG> is a sectional view taken by cutting the body along the height direction, the sectional view showing the first bit seen in the circumferential direction of the body. As shown in <FIG>, the first bit 30a includes a protruding portion <NUM> and a fixed portion <NUM>. The protruding portion <NUM> protrudes from the distal end <NUM> of the body <NUM>. The fixed portion <NUM> is provided such that the position of the fixed portion <NUM> is shifted from the distal end <NUM> of the body <NUM> toward the proximal end of the body <NUM>, and the fixed portion <NUM> is fixed to the body <NUM>. When the first bit 30a is seen in the front view, the distal end <NUM> of the first bit 30a (i.e., the distal end of the protruding portion <NUM>) is linearly sloped such that the height position of the distal end <NUM> becomes lower toward the forward side in the rotation direction of the body <NUM>.

As shown in <FIG>, in the sectional view, which is taken by cutting the body <NUM> along the height direction and which shows the first bit 30a seen in the circumferential direction of the body <NUM>, the first bit 30a includes a first lower end edge that is linearly sloped from the distal end <NUM>, such that the height position of the first lower end edge becomes higher toward the outer side of the body <NUM>. The first lower end edge extends in the circumferential direction of the body <NUM> (i.e., from the front side toward the back side of <FIG>).

Also, in the sectional view, which is taken by cutting the body <NUM> along the height direction and which shows the first bit 30a seen in the circumferential direction of the body <NUM>, the first bit 30a further includes a second lower end edge and a third lower end edge. The second lower end edge is linearly sloped from the distal end <NUM>, such that the height position of the second lower end edge becomes higher toward the inner side of the body <NUM>. The third lower end edge starts from the inner end of the second lower end edge, and bends toward the proximal end. The third lower end edge is linearly sloped such that the height position of the third lower end edge becomes higher toward the inner side of the body <NUM>. Each of the second lower end edge and the third lower end edge extends in the circumferential direction of the body <NUM> (i.e., from the front side toward the back side of <FIG>).

<FIG> are enlarged views showing a second bit of the present embodiment. <FIG> is a front view of the second bit, and <FIG> is a sectional view taken by cutting the body along the height direction, the sectional view showing the second bit seen in the circumferential direction of the body. As shown in <FIG>, the second bit 30b includes a protruding portion <NUM> and a fixed portion <NUM>. The protruding portion <NUM> protrudes from the distal end <NUM> of the body <NUM>. The fixed portion <NUM> is provided such that the position of the fixed portion <NUM> is shifted from the distal end <NUM> of the body <NUM> toward the proximal end of the body <NUM>, and the fixed portion <NUM> is fixed to the body <NUM>. When the second bit 30b is seen in the front view, the distal end <NUM> of the second bit 30b (i.e., the distal end of the protruding portion <NUM>) is linearly sloped such that the height position of the distal end <NUM> becomes lower toward the forward side in the rotation direction of the body <NUM>.

As shown in <FIG>, in the sectional view, which is taken by cutting the body <NUM> along the height direction and which shows the second bit 30b seen in the circumferential direction of the body <NUM>, the second bit 30b includes a fourth lower end edge that linearly extends from the distal end <NUM> toward the outer side of the body <NUM> at the same height position. The fourth lower end edge extends in the circumferential direction of the body <NUM> (i.e., from the front side toward the back side of <FIG>).

Also, in the sectional view, which is taken by cutting the body <NUM> along the height direction and which shows the second bit 30b seen in the circumferential direction of the body <NUM>, the second bit 30b further includes a fifth lower end edge. The fifth lower end edge is linearly sloped from the distal end <NUM>, such that the height position of the fifth lower end edge becomes higher toward the inner side of the body <NUM>. The fifth lower end edge extends in the circumferential direction of the body <NUM> (i.e., from the front side toward the back side of <FIG>).

As shown in <FIG>, a first distance D<NUM> between the distal end <NUM> of the first bit 30a and the axis AX of the body <NUM>, and a second distance D<NUM> between the distal end <NUM> of the second bit 30b and the axis AX of the body <NUM>, are different from each other. Specifically, it is clear from the comparison of <FIG> and <FIG> that the first distance D<NUM> is greater than the second distance D<NUM>.

Here, as shown in <FIG>, when the first bit 30a is seen in the front view, from the front end of the distal end <NUM> of the first bit 30a in the rotation direction, a surface extends diagonally upward and connects to the rear end of a notch <NUM> in the rotation direction. This surface is generally called a "rake face". A two-dot chain line in <FIG> is an upward extension of the rake face. A one-dot chain line in <FIG> represents a vertical plane that extends in the height direction passing through the front end of the distal end <NUM> of the first bit 30a in the rotation direction. The rake face forms an angle α with the vertical plane. In general, the angle α is referred to as a "rake angle".

Further, in <FIG>, when the rake face of the first bit 30a is positioned on the right side of the vertical plane, the rake angle α of the first bit 30a is a positive angle. On the other hand, when the rake face of the first bit 30a is positioned on the left side of the vertical plane, the rake angle α of the first bit 30a is a negative angle. It should be noted that the above definitions of the "rake face" and the "rake angle" also apply to <FIG> and <FIG>, which will be referred to below.

As shown in <FIG>, in the present embodiment, the rake angle α of the first bit 30a is a negative angle. Similarly, as shown in <FIG>, the rake angle α' of the second bit 30b is a negative angle. These rake angles α and α' are equal negative angles. It should be noted that the rake angles α and α' may be determined by mounting angles at which the first bit 30a and the second bit 30b are mounted to the body <NUM>, respectively. Alternatively, the rake angles α and α' may be determined by grinding the distal end of the first bit 30a and the distal end of the second bit 30b by grinding stone.

It should be noted that in a case where the diameter of the body main part <NUM> is about <NUM>, the thickness of the fixed portion <NUM> of each of the first bit 30a and the second bit 30b (i.e., the dimension of the fixed portion <NUM> in the radial direction of the body <NUM>) may be about <NUM>. Also, the distance between the distal end <NUM> of the protruding portion <NUM> and the distal end <NUM> of the body <NUM> (and the distance between the distal end <NUM> of the protruding portion <NUM> and the distal end <NUM> of the body <NUM>) may be about <NUM>.

As shown in <FIG>, at the distal end of the body <NUM>, the aforementioned notch <NUM> is formed adjacently to the first bit 30a at a position forward of the first bit 30a in the rotation direction of the body <NUM>. The notch <NUM> is intended for discharging swarf that is generated during cutting by the first bit 30a. It should be noted that the same notches <NUM> are formed for the five first bits 30a, respectively. Similarly, as shown in <FIG>, at the distal end of the body <NUM>, the same notch <NUM> is formed adjacently to the second bit 30b at a position forward of the second bit 30b in the rotation direction of the body <NUM>. It should be noted that the same notches <NUM> are formed for the five second bits 30b, respectively.

When each of the first bit 30a and the second bit 30b is seen the front view, each notch <NUM> has a semicircular shape such that the notch <NUM> protrudes from the distal end of the body <NUM> toward the proximal end of the body <NUM>. At the distal end of the body <NUM>, a width X of each notch <NUM> in the circumferential direction is less than or equal to <NUM>. It should be noted that the width X may be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>. Alternatively, the width X may be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>. In the present embodiment, entirely from the distal end to the proximal end of each notch <NUM>, the width of the notch <NUM> in the circumferential direction of the body <NUM> is less than or equal to <NUM>. Also, the proximal ends of the notches <NUM> are positioned closer to the distal end of the body <NUM> than the proximal ends of the fixed portions <NUM> and <NUM> of the bits <NUM> (i.e., the first and second bits 30a and 30b).

In the core cutter <NUM> according to the present embodiment, the width of each notch <NUM>, which is formed in the body <NUM> for the purpose of discharging the swarf, is less than or equal to <NUM> in the circumferential direction at the distal end of the body <NUM>. Thus, the width of each notch is sufficiently smaller than an expected thickness of a rising portion of irregularities of a workpiece (this will be described below in detail with reference to <FIG>). Consequently, even in the case of cutting a workpiece having irregularities, the notches can be prevented from biting into the irregularities.

In the core cutter <NUM> according to the present embodiment, since the rake angles α and α' of the bits <NUM> (i.e., the first and second bits 30a and 30b) are negative angles, the strength of the bits <NUM> is improved, which consequently makes it possible to suppress damage to the bits <NUM>.

In the core cutter <NUM> according to the present embodiment, the width of each notch <NUM> in the circumferential direction at the distal end of the body <NUM> may be set to be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>. This setting makes it possible to realize, in a balanced manner, both preventing the biting into the irregularities and sufficiently discharging the swarf.

In the core cutter <NUM> according to the present embodiment, the width of each notch <NUM> in the circumferential direction at the distal end of the body <NUM> may be set to be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>. This setting makes it possible to realize, in a more balanced manner, both preventing the biting into the irregularities and sufficiently discharging the swarf.

The core cutter <NUM> according to the present embodiment includes the plurality of bits <NUM>, and the notches <NUM> are formed for the respective bits <NUM>. According to this configuration, the workpiece is cut by the plurality of bits <NUM>. This makes it possible to reduce the load on each of the bits <NUM>, and thereby damage to each of the bits <NUM> can be further suppressed.

In the present embodiment, the first distance D<NUM> between the distal end <NUM> of the first bit 30a and the axis AX of the body <NUM>, and the second distance D<NUM> between the distal end <NUM> of the second bit 30b and the axis AX of the body <NUM>, are different from each other, and the first and second bits 30a and 30b are arranged alternately in the circumferential direction of the body <NUM>. According to this configuration, the workpiece can be properly cut by an amount corresponding to the thickness of the bits <NUM>. Therefore, while cutting the workpiece, the bits <NUM> and the body <NUM> can smoothly move forward in the thickness direction of the workpiece.

In the present embodiment, entirely from the distal end to the proximal end of each notch <NUM> formed in the body <NUM>, the width of the notch <NUM> in the circumferential direction of the body <NUM> is less than or equal to <NUM>, and also, the proximal ends of the notches <NUM> are positioned closer to the distal end of the body <NUM> than the proximal ends of the fixed portions <NUM> and <NUM> of the bits <NUM>. This makes it possible to more assuredly prevent the biting into the irregularities of the workpiece.

In the present embodiment, the thickness of the distal end portion of the body main part <NUM> is greater than the thickness of the remaining portion of the body main part <NUM>, and the bits <NUM> are fixed to the distal end portion. This makes it possible to increase the thickness of the bits <NUM>, thereby improving the durability thereof. Moreover, since the area of contact between the body main part <NUM> and the fixed portions <NUM> of the bits <NUM> can be increased, the bits <NUM> can be firmly fixed to the body <NUM>.

Next, with reference to <FIG>, one example of a cutting method using the core cutter <NUM> according to the above-described embodiment is described. It should be noted that the cutting method described herein is not limited to a case where the cutting method is performed by using the core cutter <NUM> according to the above-described embodiment. For example, the cutting method may be performed by using a core cutter <NUM>' described below (see <FIG>), a core cutter <NUM>" described below (see <FIG>), or any other core cutter.

First, a first step is performed, which is a step of preparing the core cutter <NUM> according to the above-described embodiment, an electric drill <NUM> to which the core cutter <NUM> is to be mounted as a distal end tool, and a workpiece W having irregularities on the surface thereof.

Next, a second step is performed, which is a step of mounting the core cutter <NUM> prepared in the first step to the electric drill <NUM>. <FIG> shows a state where the core cutter <NUM> is mounted to the electric drill <NUM> in the second step. <FIG> shows the workpiece W, which has irregularities and which is prepared in the first step.

As shown in <FIG>, the electric drill <NUM> includes an electric drill body <NUM> and a mounting chuck <NUM>. First, a center drill <NUM> and a shank (not shown) are mounted to the core cutter <NUM>. The center drill <NUM> is disposed in a manner to extend on the axis AX in the interior space of the body <NUM> and protrude from the opening at the distal end <NUM> of the body <NUM>. The unshown shank is disposed in a manner to extend from the proximal end portion <NUM> of the body <NUM> toward the opposite side to the center drill <NUM>. Then, the shank is held by the mounting chuck <NUM> of the electric drill <NUM>. In this manner, the core cutter <NUM> is mounted to the electric drill <NUM> as shown in <FIG>.

As shown in <FIG>, the workpiece W is a plate-shaped deck plate having four projections C on the surface thereof. It should be noted that the workpiece W is a metal workpiece. The four projections C are parallel to each other and extend in the length direction of the workpiece W. As shown in <FIG>, which will be referred to below, each of the four projections C is formed by bending a part of the plate-shaped deck plate. Accordingly, the thickness of each of the four projections C is the same as the thickness of the remaining part of the plate-shaped deck plate. The bottom face of each projection C is open, and thus each projection C is formed as a hollow projection.

By the electric drill <NUM>, the core cutter <NUM> is rotated about the rotational axis, which is the axis AX of the core cutter <NUM>. The distal end side of the rotating core cutter <NUM> is pressed against a rising portion Ca of the irregularities (specifically, the rising portion Ca of a projection C) along the rising direction of the rising portion Ca, and thereby a third step of cutting a part of the irregularities (specifically, a part of the projection C) is performed, which is shown in <FIG> is a perspective view showing the third step being performed. <FIG> is a sectional view taken by cutting the projection C of the workpiece W along the height direction, the sectional view showing the first bit 30a seen in the length direction of the projection C.

By cutting the workpiece W as in the above third step, as shown in <FIG>, while the cutting is being performed, a part of the opening of the distal end <NUM> of the body <NUM> is not blocked by the workpiece W, and is thus exposed. Accordingly, swarf generated during the cutting is discharged through the part of the opening. Therefore, as previously described in the above embodiment, the notches <NUM> for discharging the swarf can be made smaller than those in the conventional art. Moreover, unlike the conventional art, it is unnecessary to form gullet grooves in the distal end portion of the body main part <NUM> adjacently to the bits <NUM> for the purpose of discharging the swarf generated during the cutting toward the proximal end of the body <NUM>. For this reason, the area of contact between the body main part <NUM> and the fixed portions <NUM> of the bits <NUM> can be increased, and thereby the bits <NUM> can be firmly fixed to the body <NUM>.

Further, as shown in <FIG>, the width of the notch <NUM> in the circumferential direction at the distal end of the body <NUM> is less than or equal to <NUM>, which is sufficiently smaller than an expected thickness of a rising portion of the irregularities (specifically, the rising portion of a projection C) of the workpiece. Consequently, even in the case of cutting the workpiece W having irregularities, the notches <NUM> can be prevented from biting into the irregularities.

From the foregoing description, numerous modifications and other embodiments of the present invention are obvious to a person skilled in the art. Therefore, the foregoing description should be interpreted only as an example and is provided for the purpose of teaching the best mode for carrying out the present invention to a person skilled in the art. The structural and/or functional details may be substantially modified without departing from the spirit of the present invention.

With reference to <FIG>, a first variation of the core cutter according to the one embodiment of the present invention is described. <FIG> show the first variation of the core cutter. <FIG> is a front view, and <FIG> is a bottom view. <FIG> is an enlarged front view showing the bit of the first variation of the core cutter.

It should be noted that the core cutter <NUM>' of the first variation is the same in structure as the above-described core cutter <NUM> except the bits <NUM>, the notches <NUM> formed in the body <NUM>, and the following thickness feature of the body main part <NUM>: the thickness of the body main part <NUM> is the same entirely from the distal end to the proximal end of the body main part <NUM>, including its distal end portion. Therefore, common components between the above-described core cutter <NUM> and the core cutter <NUM>' of the first variation are denoted by the same reference signs, and repeating the same descriptions is avoided herein.

As shown in <FIG>, the core cutter <NUM>' of the present variation includes ten tipped bits <NUM>, which are disposed in a manner to protrude from the distal end of the body <NUM>. It should be noted that, unlike the above-described embodiment, all the bits <NUM> of the present variation have the same shape.

It should be noted that, in a case where the diameter of the body main part <NUM> is about <NUM>, the thickness of the fixed portion <NUM> of each of the bits <NUM> (i.e., the dimension of the fixed portion <NUM> in the radial direction of the body <NUM>) may be about <NUM>. Also, the distance between the distal end <NUM> of the protruding portion <NUM> and the distal end <NUM> of the body <NUM> may be about <NUM>.

As shown in <FIG>, in the core cutter <NUM>' of the present variation, an auxiliary notch <NUM> is formed adjacently to each bit <NUM> at a position rearward of the bit <NUM> in the rotation direction of the body <NUM>.

As shown in <FIG>, in the core cutter <NUM>' of the present variation, the notch <NUM> is formed adjacently to each bit <NUM> at a position forward of the bit <NUM> in the rotation direction of the body <NUM>, and the rake angle α" of the bit <NUM> is a negative angle. Also, the width of the notch <NUM> in the circumferential direction at the distal end of the body <NUM> is less than or equal to <NUM>. It should be noted that the width may be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>. Alternatively, the width may be greater than or equal to <NUM>. <NUM>, but less than or equal to <NUM>.

The notch <NUM> of the present variation includes a distal end portion <NUM> and a main portion <NUM>. When the bit <NUM> is seen in the front view, the distal end portion <NUM> extends rectangularly in the height direction, and the main portion <NUM> is continuous with the proximal end of the distal end portion <NUM>. The main portion <NUM> of the notch <NUM> has an end edge. From the proximal end of the rotational-direction forward end edge of the distal end portion <NUM> of the notch <NUM>, the end edge of the main portion <NUM> protrudes forward in the rotation direction and is curved in a substantially arc shape, and then, at a position that is adjacent to and forward of the proximal end portion of the bit <NUM> in the rotation direction, the end edge is curved again in a substantially arc shape so as to protrude downward.

The width of the distal end portion <NUM> of the notch <NUM> in the circumferential direction of the body <NUM> is less than or equal to <NUM>; the width of the main portion <NUM> of the notch <NUM> in the circumferential direction of the body <NUM> is greater than <NUM>; and the proximal end of the main portion <NUM> is positioned closer to the proximal end of the body <NUM> than the proximal end of the fixed portion <NUM> of the bit <NUM>. This configuration makes it possible to realize, in a balanced manner, both preventing the notches from biting into the irregularities of the workpiece W and sufficiently discharging the swarf.

With reference to <FIG>, a second variation of the core cutter according to the one embodiment of the present invention is described. <FIG> show the second variation. <FIG> is a front view, and <FIG> is a bottom view. <FIG> is an enlarged front view showing the bit of the second variation. It should be noted that the core cutter <NUM>" of the second variation is the same in structure as the above-described core cutter <NUM>' of the first variation, except the rake angles of the bits <NUM>. Therefore, common components between the above-described core cutter <NUM>' and the core cutter <NUM>" of the second variation are denoted by the same reference signs, and repeating the same descriptions is avoided herein.

As shown in <FIG>, the core cutter <NUM>" of the present variation includes the cylindrical body <NUM> and the tipped bits <NUM>. The tipped bits <NUM> are disposed in a manner to protrude from the distal end of the body <NUM>. It should be noted that, similar to the above-described core cutter <NUM> (see <FIG>) and core cutter <NUM>' (see <FIG>), the core cutter <NUM>" of the present variation includes <NUM> tipped bits <NUM>.

As shown in <FIG>, in the core cutter <NUM>" of the present variation, the notch <NUM> is formed adjacently to each bit <NUM> at a position forward of the bit <NUM> in the rotation direction of the body <NUM>. The rake angle α‴ of the bit <NUM> is a positive angle, and the width X‴ of the notch <NUM> in the circumferential direction at the distal end of the body <NUM> is less than or equal to <NUM>.

In the core cutter <NUM>"according to the present variation, since the rake angle α‴ of the bit <NUM> is a positive angle, the cutting quality of the core cutter <NUM>" can be improved compared to a case where the rake angle is a negative angle. It should be noted that advantageous effects provided owing to the feature that the width X‴ of the notch <NUM> in the circumferential direction at the distal end of the body <NUM> is less than or equal to <NUM> are the same as those provided in the above-described embodiment and first variation. Therefore, the description thereof is not repeated herein.

Next, with reference to <FIG> and <FIG>, a first variation of the cutting method, which is performed by using the core cutter <NUM>"according to the second variation, is described. <FIG> is a perspective view showing a state where a jig that is used together with the core cutter in the cutting method according to the present variation is placed on a workpiece. <FIG> is a schematic diagram showing a state where the workpiece is being cut by the cutting method according to the present variation.

First, the core cutter <NUM>" according to the second variation, an electric drill to which the core cutter <NUM>" is to be mounted as a distal end tool, a jig <NUM>, and a workpiece W' having irregularities on the surface thereof, are prepared.

As shown in <FIG>, the jig <NUM> includes a disc-shaped base portion <NUM> and a cylinder <NUM> (a cylindrical portion). The cylinder <NUM> is provided upright at the center of the upper surface of the base portion <NUM>. A through-hole <NUM> is drilled in the jig <NUM>, and has the same diameter from the bottom surface of the base portion <NUM> to the upper end of the cylinder <NUM>. The diameter of the through-hole <NUM> corresponds to the external diameter of the body main part <NUM> of the core cutter <NUM>". Specifically, the diameter of the through-hole <NUM> of the jig <NUM> is slightly greater than the external diameter of the body main part <NUM> of the core cutter <NUM>" so that, as described below, the body main part <NUM> of the core cutter <NUM>" can be inserted into the through-hole <NUM> while restricting movement of the body main part <NUM> in the radial direction.

Further, as shown in <FIG>, the workpiece W' is configured as a plate-shaped deck plate having at least two projections C' on the surface thereof (hereinafter, the at least two projections C' are simply referred to as "two projections C‴ or "one projection C' and the other projection C‴ unless they need to be specifically referred to as "at least two projections C'". It should be noted that the workpiece W' is a metal workpiece. The two projections C' are parallel to each other and extend in the width direction of the workpiece W'. Each of the two projections C' is formed by bending a part of the plate-shaped deck plate. Accordingly, the thickness of each of the two projections C' is the same as the thickness of the remaining part of the plate-shaped deck plate. Also, the bottom face of each projection C' is open, and thus each projection C' is formed as a hollow projection.

When seen in the width direction of the workpiece W', each of the two projections C' has a bottom face and an upper face. Hereinafter, the bottom face is referred to as "the lower bottom" and the upper face is referred to as "the upper bottom". The lower bottom is longer than the upper bottom. That is, each projection C' is in the shape of a trapezoid. It should be noted that, as mentioned above, the bottom face of each projection C' is open. According to this configuration, the two legs of the trapezoid are respective rising portions Ca' of the projection C'. It should be noted that the trapezoid is an isosceles trapezoid. Accordingly, when seen in the width direction of the workpiece W', the two rising portions Ca' of each projection C' have the same length.

When seen in the width direction of the workpiece W', one end (the right end in <FIG> and <FIG>) of the lower bottom of one projection C' (the projection C' present on the left side in <FIG> and <FIG>, and the other end (the left end in <FIG> and <FIG>) of the lower bottom of the other projection C' (the projection C' present on the right side in <FIG> and <FIG>), are connected by a connector that has the same length as the length of the upper bottom of the one projection C' (and the same length as the length of the upper bottom of the other projection C'). Accordingly, when the workpiece W' is placed upside down, grooves are formed, which form the same trapezoid as the one projection C' (or the other projection C') between the one projection C' and the other projection C'.

Next, the jig <NUM> is placed on the workpiece W', which is shown in <FIG>. As shown in <FIG>, the jig <NUM> is placed on the workpiece W', such that one side of the bottom surface of the base portion <NUM> of the jig <NUM> is in contact with the upper face of the one projection C', and the other side of the bottom surface of the base portion <NUM> is in contact with the upper face of the other projection C' (i.e., in a manner to cover a part of the upper face of the groove formed between the one projection C' and the other projection C'). It should be noted that a nonslip member <NUM> is disposed between the bottom surface of the base portion <NUM> and the upper faces of the respective projections C' of the workpiece W'.

Also, the jig <NUM> is placed on the workpiece W' such that, when seen in the width direction of the workpiece W' (i.e., in the view shown in <FIG>), the position of one edge of the through-hole <NUM> (the left-side edge in <FIG>) at the bottom surface of the jig <NUM> coincides with the position of the bottom face of the groove of the workpiece W' in the length direction of the workpiece W', and also, the position of the other edge of the through-hole <NUM> (the right-side edge in <FIG>) at the bottom surface of the jig <NUM> coincides with the middle part of the rising portion Ca' of the other projection C' in the length direction of the workpiece W'.

Further, the core cutter <NUM>" previously described with reference to <FIG> is mounted to the electric drill as a distal end tool. It should be noted that the electric drill has the same structure as that of the electric drill <NUM> previously described with reference to <FIG>, except the following points: in the electric drill <NUM> shown in <FIG>, the center drill <NUM> is disposed in a manner to protrude from the opening at the distal end <NUM> of the body <NUM>; and the shank (not shown) is disposed in a manner to extend from the proximal end portion <NUM> of the body <NUM> toward the opposite side to the center drill <NUM>. Therefore, repeating the same descriptions is avoided herein.

In the present variation, a rod-shaped rotor <NUM> is held by the mounting chuck of the electric drill, and the proximal end of the core cutter <NUM>" is mounted to a mounting portion <NUM> provided on the distal end of the rotor <NUM> (see <FIG>). At the time, the rotor <NUM> of the electric drill is disposed in a manner to extend on the same straight line as the axis AX of the core cutter <NUM>".

Then, as shown in <FIG>, by (the rotor <NUM> of) the electric drill, the core cutter <NUM>" is rotated about the rotational axis, which is the axis AX of the core cutter <NUM>". The rotating core cutter <NUM>" is, from the upper end side of the jig <NUM>, inserted into the through-hole <NUM> of the jig <NUM>, which is placed on the workpiece W'. At the time, in the present variation, parts of the base portion <NUM> of the jig <NUM>, the parts being placed on the upper ends of the respective two projections C' of the workpiece W', are stepped on by both feet S of a worker and thereby fixed while the core cutter <NUM>" is being inserted into the through-hole <NUM> of the jig <NUM> from the upper end side of the jig <NUM>.

While rotating, the distal end portion of the core cutter <NUM>" protrudes from the bottom surface side of the through-hole <NUM> of the jig <NUM>. Then, the distal end side of the core cutter <NUM>" is pressed against the rising portion Ca' of the irregularities (specifically, the rising portion Ca' of the other projection C') along the rising direction of the rising portion Ca', and thereby a part of the irregularities (specifically, a part of the other projection C') is cut. It should be noted that the expression "the distal end side of the core cutter <NUM>" is pressed. along the rising direction of the rising portion Ca' of the projection C‴ herein encompasses not only a case where the pressing direction of the core cutter <NUM>" and the rising direction of the rising portion Ca' of the projection C' are parallel to each other, but also a case where these directions are inclined relative to each other by a certain angle.

Here, assume a case where the rising portion Ca' of the other projection C' is cut only by the core cutter <NUM>" and the electric drill without using the jig <NUM>. At the time, if the distal end of the core cutter <NUM>" is pressed against the rising portion Ca' to cut the rising portion Ca', then the core cutter <NUM>" oscillates due to, for example, the fact that the rising portion Ca' is inclined. Therefore, it is difficult to cut the workpiece W' as desired.

On the other hand, by using the jig <NUM>, the distal end of the core cutter <NUM>" is pressed against the rising portion Ca' of the other projection C' in a state where a part of the core cutter <NUM>" is positioned within the through-hole <NUM> of the jig <NUM>. That is, movement of the core cutter <NUM>" in the radial direction is restricted by the jig <NUM>, and thereby the oscillation of the core cutter <NUM>" can be prevented. Consequently, the cutting method according to the present variation makes it possible to cut, as desired, the workpiece W' having irregularities.

Further, in the present variation, the worker performs the cutting work while fixing the base portion <NUM> by stepping on the base portion <NUM> with both of his or her feet S. This makes it possible to cut the workpiece W' as desired more assuredly. Still further, the nonslip member <NUM> is provided between the bottom surface of the base portion <NUM> and the upper faces of the respective projections C' of the workpiece W'. This makes it possible to cut the workpiece W' as desired even more assuredly.

Next, with reference to <FIG>, a second variation of the cutting method, which is performed by using the core cutter <NUM>" according to the second variation, is described. <FIG> is a schematic diagram showing a state where a workpiece is being cut by the cutting method according to the present variation. It should be noted that the cutting method according to the present variation is the same as the above-described cutting method according to the first variation except the manner of fixing the jig <NUM> to the workpiece W'. Therefore, common components between the first variation and the second variation are denoted by the same reference signs, and repeating the same descriptions is avoided herein.

In the cutting method according to the present variation, as shown in <FIG>, parts of the base portion <NUM> of the jig <NUM>, the parts being placed on the upper ends of the respective two projections C' of the workpiece W', are fixed by screws (fixing members) <NUM>. In a state where the jig <NUM> is thus fixed to the workpiece W', the core cutter <NUM>" may be inserted into the through-hole <NUM> of the jig <NUM> from the upper end side of the jig <NUM> to cut a part of the workpiece W'.

It should be noted that the fixing members are not limited to the screws <NUM>. For example, each fixing member may be a fixing member between which an edge of the jig <NUM> and an edge of the workpiece W', which are disposed one on top of the other, are sandwiched in their thickness direction, and thereby the jig <NUM> may be fixed to the workpiece W'. Alternatively, each fixing member may be configured differently.

In the above-described embodiment and variations, the body <NUM> includes the body main part <NUM> and the proximal end portion <NUM>. The proximal end portion <NUM> is continuous with the proximal end surface of the body main part <NUM>, and has a less diameter than that of the body main part <NUM>. However, this is a non-limiting example. As an alternative example, the body <NUM> may be formed such that the diameter of the body <NUM> is constant from its distal end to the proximal end. This makes it possible to readily manufacture the body main part <NUM>.

In the above-described embodiment and variations, each of the core cutters <NUM>, <NUM>', and <NUM>" is mounted to the electric drill <NUM> and rotated. However, each of these cases is a non-limiting example. As an alternative example, the core cutter <NUM> may be mounted to a driver drill, an impact drill, or a hammer drill. It should be noted that, in a case where the electric drill is an impact drill or a hammer drill, it is preferable to use the electric drill in a rotation mode that does not cause impacting or hammering action.

Claim 1:
A core cutter (<NUM>) comprising:
a cylindrical body (<NUM>);
a tipped bit (<NUM>) that is disposed in a manner to protrude from a distal end of the body (<NUM>); and
a notch (<NUM>) that is formed, at the distal end of the body (<NUM>), adjacently to the bit (<NUM>) at a position forward of the bit (<NUM>) in a rotation direction of the body (<NUM>), wherein
the core cutter (<NUM>) is configured to cut a workpiece (W) with the bit (<NUM>) when the body (<NUM>) is rotated about a rotational axis that is an axis (AX) of the body (<NUM>),
wherein
a width of the notch (<NUM>) in a circumferential direction of the body (<NUM>) at the distal end of the body (<NUM>) is less than or equal to <NUM>, characterized in that
the bit (<NUM>) includes:
a protruding portion (<NUM>) that protrudes from the distal end of the body (<NUM>); and
a fixed portion (<NUM>) fixed to the body (<NUM>), the fixed portion (<NUM>) being provided such that a position of the fixed portion (<NUM>) is shifted from the distal end of the body (<NUM>) toward a proximal end of the body (<NUM>), and
entirely from a distal end of the notch (<NUM>) to a proximal end of the notch (<NUM>), the width of the notch (<NUM>) in the circumferential direction of the body (<NUM>) is less than or equal to <NUM>, and the proximal end of the notch (<NUM>) is positioned closer to the distal end of the body (<NUM>) than a proximal end of the fixed portion (<NUM>) of the bit (<NUM>).