CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry according to 35 U.S.C. 371 of PCT Application No. PCT/JP2018/021251 filed on Jun. 1, 2018, which claims priority to Japanese Application No. 2017-109889 filed on Jun. 2, 2017, which are entirely incorporated herein by reference.

TECHNICAL FIELD

The present aspect relates to a rotary tool.

BACKGROUND ART

As drills including a small diameter portion on a tip side of a drill body and a large diameter portion on a rear end side of the drill body, stepped drills described in, for example, Patent Documents 1 and 2 are known. Stepped drills allow fabrication such as boring, stepped boring, and chamfering and enables efficient machining. In a drill described in JP 2010-131736 A (Patent Document 1), the helix angle of the small diameter portion and the helix angle of the large diameter portion are the same. Additionally, in a drill described in JP 2014-054680 A (Patent Document 2), the helix angle of the small diameter portion is smaller than the helix angle of the large diameter portion.

In the stepped drill described in Patent Document 1, the helix angle of the small diameter portion and the helix angle of the large diameter portion are the same. In a case where the helix angles of both the small and large diameter portions are increased in order to reduce cutting resistance of the small diameter portion, deflection of the large diameter portion may be more significant. Additionally, in a case where the helix angles of both the small and large diameter portion are reduced in order to reduce deflection of the large diameter portion, the cutting resistance of the small diameter portion is increased, possibly leading to more significant run-out.

In the stepped drill described in Patent Document 2, the helix angle of the small diameter portion is smaller than the helix angle of the large diameter portion. Thus, in a case where the helix angle of the small diameter portion is increased in order to reduce the cutting resistance of the small diameter portion, since the helix angle of the large diameter portion is larger than the helix angle of the small diameter portion, deflection of the large diameter portion may be more significant. Additionally, in a case where the helix angle of the large diameter portion is reduced in order to reduce deflection of the large diameter portion, since the helix angle of the small diameter portion is smaller than the helix angle of the large diameter portion, the small diameter portion has increased cutting resistance, possibly leading to more significant run-out.

SUMMARY OF INVENTION

A rotary tool according to a non-limiting aspect includes a body having a rotation axis and a rod like shape extending from a first end to a second end. The body includes: a first part including the first end; a second part located closer to the second end than the first part and having a larger outside diameter than the first part; a cutting edge located at a side of the first end; a ridge portion located in the first part and the second part, connected to the cutting edge and helically extending from the cutting edge toward the second end; and a flute located along the cutting edge and the ridge portion. The flute includes: a first flute located at the first part and having a first helix angle; and a second flute located at the second part and having a second helix angle. The second helix angle is smaller than the first helix angle.

