Drill and method of manufacturing machined product

1. A drill, having an elongated shape and a rotation axis, and comprising:

a drilling portion located on a first end side thereof, comprising:

a first helical flute; and

a first cutting edge located on the first end side of the first helical flute;

a shank portion located on a second end side thereof;

and

a tapered portion located between the drilling portion and the shank portion, having a diameter larger on the second end side than on the first end side, and comprising:

a second helical flute connected to the first helical flute;

a second cutting edge located on the first end side of the second helical flute;

a chamfered part located along the second cutting edge, and becoming smaller gradually as moving toward the first end side; and

a connection part having a curved surface, and connecting the second cutting edge and the drilling portion,

wherein w/L is in the range of 0.0015-0.5, where L is a length of the second cutting edge in a front view of the first end, and w is a width of an outer peripheral end of the chamfered part in a direction parallel to the rotation axis.

2. The drill according to claim 1 , wherein the chamfered part comprises a terminal end on a side of the rotation axis at a position in connection with the connection part.

3. The drill according to claim 1 , wherein a second helix angle of the second helical flute is larger than a first helix angle of the first helical flute.

4. The drill according to claim 1 , wherein the chamfered part comprises an axial inclination angle in the range of 0-30°.

5. The drill according to claim 1 , wherein a first axial inclination angle of the second helical flute at a side of the rotation axis is smaller than a second axial inclination angle of the second helical flute at a side of the outer periphery.

6. The drill according to claim 1 , wherein the second cutting edge comprises a clearance angle in the range of 5-30°.

7. The drill according to claim 1 , wherein the drilling portion comprises:

a first leading edge extending from an outer peripheral end of the first cutting edge toward the second end side; and

a margin part at an outer peripheral part of the drilling portion in contact with the first leading edge.

8. The drill according to claim 7 , wherein a part of the margin part at a side of the first helical flute comprises a cutout on a side of the tapered portion.

9. The drill according to claim 7 , wherein the drilling portion comprises a guide part having a larger width than the margin part and located at a side of the second end connecting to the connection part.

10. The drill according to claim 1 , wherein a radial rake of the second cutting edge is in the range of −5° to −25°.

11. The drill according to claim 1 , wherein the drilling portion comprises:

a margin part located at a front edge of an outer peripheral part of the drilling portion in a rotation direction of the drill; and

a small margin part located on a side of the tapered portion of the drilling portion, and having a cutout on a side of the first helical flute of the margin part.

12. The drill according to claim 11 , wherein the cut out of the small margin part comprises a concave curved surface with respect to an opening part of the first helical flute in a sectional view.

13. The drill according to claim 11 , wherein a second inclination angle at an end of the small margin part is smaller than a first inclination angle at an end of the margin part.

14. The drill according to claim 11 , wherein a rake angle at the second cutting edge is smaller than an inclination angle at an end of the small margin part.

15. The drill according to claim 11 , wherein a helix angle of the first helical flute at the small margin part is larger than a helix angle of the first helical flute at the margin part.

16. The drill according to claim 1 , wherein the drilling portion comprises

a small diameter part located on the first end side,

a large diameter part on the second end side,

a step part located between the small diameter part and the large diameter part, and

a stepped cutting edge located at a side end edge of the step part of the first helical flute, and

wherein the large diameter part comprises

a first large diameter part comprising the margin part disposed on a side of the small diameter part, and comprising no cutout on a side of the first helical flute, and

a second large diameter part comprising the small margin part disposed a side of the shank portion, and comprising a cutout on a side of the first helical flute of the margin part.

17. The drill according to 16 , wherein a width of the small margin part of the second large diameter part is smaller than a width of the margin part of the first large diameter part.

18. The drill according to claim 16 , wherein the small diameter part further comprises:

the margin part at a front edge of the outer peripheral part in a rotation direction of the drill; and

a width of the margin part in the small diameter part is smaller than a width of the margin part in the first large diameter part.

19. The drill according to claim 16 , wherein, in a side view, a front end angle of the small diameter part is in the range of 90-130°, and

an angle between inclination angles of the step part is in the range of 130-150° and is larger than the front end angle.

20. A method of manufacturing a machined product, comprising:

rotating a drill according to claim 1 ;

drilling a hole by causing contact between the first cutting edge of the drill being rotated and a workpiece;

cutting an opening of the drilled hole by causing contact between the second cutting edge of the drill being rotated and the workpiece; and

pulling the drill out from a hole formed in the workpiece by separating the workpiece and the drill from each other.