| CPC B23B 51/0003 (2022.01) [B23B 51/02 (2013.01); B23B 2251/02 (2013.01); B23B 2251/04 (2013.01); B23B 2251/047 (2022.01); B23B 2251/182 (2022.01); B23B 2251/202 (2013.01); B23B 2251/241 (2013.01)] | 22 Claims |
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1. A cutting head (20) rotatable about a first axis (A1) in a direction of rotation (DR), the cutting head having three-fold rotational symmetry about the first axis (A1) and comprising:
an intermediate portion (22) having an integer number N=3 circumferentially spaced apart peripheral surfaces (26), each peripheral surface (26) having a leading edge (28), and the plurality of leading edges (28) defining a cutting diameter (DC); and
a tip portion (24) having an axially forwardmost tip point (NT) contained in the first axis (A1) and N front surfaces (30), each front surface (30) having a radially extending front cutting edge (31) which comprises an outer cutting edge (32) extending radially inwardly from one of the leading edges (28) and an inner cutting edge (34) extending radially inwardly from said outer cutting edge (32), each front surface (30) including a clearance surface (36) adjacent its associated outer and inner cutting edges (32, 34), each inner cutting edge (34) adjoining its associated outer cutting edge (32) at a cutting edge transition point (NR),
wherein:
in a first cross-section taken parallel to the first axis (A1) and intersecting any one of the outer cutting edges (32), an outer rake surface (40) adjacent to said outer cutting edge (32) is inclined at a positive outer rake angle (α1); and
in any second cross-section taken parallel to the first axis (A1) and intersecting any one of the inner cutting edges (34), an inner rake surface (42) adjacent to said inner cutting edge (34) is inclined at a negative inner rake angle (α2),
wherein:
each outer rake surface (40) is disposed on a head flute (44) extending axially rearwardly from the tip portion (24) and intersecting one of the leading edges (28);
the cutting head (20) has an axially rearward facing bottom surface (56), and each head flute (44) intersects the bottom surface (56);
each inner rake surface (42) is disposed on a gash (46) extending axially rearwardly from the tip portion (24) and intersecting one of the head flutes (44),
each gash (46) has a gash path (GP) defined by a plurality of gash midpoints from a series of cross-sections taken in planes perpendicular to the first axis (A1) and intersecting the gash (46) along its axial extent, each gash midpoint being located at a midpoint of a segment of the associated cross-section having a minimum radius;
each gash path (GP) extends to a gash path end point (NP) located a first distance (d1) axially rearward of the forwardmost tip point (NT);
the first distance (d1) is greater than thirty percent of the cutting diameter (DC); and
each gash path end point (NP) is located radially further from the first axis (A1) than any one of the cutting edge transition points (NR);
wherein:
in a cross-section taken in a first horizontal plane (PH1) perpendicular to the first axis (A1) and intersecting the plurality of inner cutting edges (34), each gash (46) has a concave shaped first profile (P1) which is continuously curved along the entire length of said profile (P1);
the first profile (P1) has a minimum first radius (R1) measured along a first segment (S1) thereof, the first segment (S1) containing a first gash midpoint (NA1); and
the minimum first radius (R1) is greater than six percent of the cutting diameter (DC), and
wherein:
the bottom surface (56) is perpendicular to the first axis (A1) and located a second distance (d2) axially rearward of the tip point (NT),
the first distance (d1) is greater than seventy percent of the second distance (d2), and
the first distance (d1) is less than ninety percent of the second distance (d2).
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