Rotatable cutting head having torque transmission surfaces on a mounting protuberance and rotary cutting tool

A rotary cutting tool (50) comprising, in combination:

• a tool shank (52) extending along a shank axis (AS) and having a head receiving pocket (54) at a forward end (56) thereof, the head receiving pocket (54) comprising circumferentially spaced apart fixation portions (58), each fixation portion (58) having an axially forward-facing shank support surface (60), and
• a cutting head (20) rotatable about a head axis (AH) in a direction of cutting rotation (RC), the head axis (AH) establishing an axial forward direction (DF) and an axial rearward direction (DR), the cutting head comprising:
• a cap portion (22) having N cutting portions (26) circumferentially alternating with N head flutes (28), and a cap base surface (30) facing in the axial rearward direction (DR);
• and
• a mounting protuberance (24) joined to the cap portion (22), extending axially rearwardly from the cap base surface (30), the mounting protuberance (24) having:
• a mounting end surface (36) distal from the cap portion (22), facing in the axial rearward direction (DR), and
• N circumferentially spaced apart engagement portions (34), each engagement portion (34) including a radially outward facing clamping surface (38), and a torque transmission surface (40) facing opposite the direction of cutting rotation (RC),
• wherein:
• N is an integer greater than 1;
• in a cross-section taken in a first head plane (PH1) perpendicular to the head axis (AH), intersecting the N engagement portions (34) and passing through the N clamping surfaces (38) and the N torque transmission surfaces (40):
• a first imaginary circle (C1) centered about the head axis (AH) and having a first diameter (D1) circumscribes the N clamping surfaces (38),
• a second imaginary circle (C2) centered about the head axis (AH) and having a second diameter (D2), is defined by N radially outermost torque points (NTO) of the N torque transmission surfaces (40), and
• the second diameter (D2) is greater than ninety percent and less than one hundred percent of the first diameter (D1);
• and
• in an assembled position of the tool:
• the cutting head (20) is releasably secured to the head receiving pocket (54);
• the cap base surface (30) faces the N shank support surfaces (60);
• the head axis (AH) is coincident with the shank axis (AS);
• each clamping surface (38) is in contact with a radially inward facing abutment surface (64) of one of the fixation portions (58);
• each torque transmission surface (40) is in contact with a drive surface (66) of one of the fixation portions (58), each drive surface (66) facing in the direction of cutting rotation (RC);
• each abutment surface (64) is circumferentially spaced apart from its associated drive surface (66) by a fixation recess (72) having a recess surface (74), and
• in a cross-section taken in a first tool plane (PT1) coincident with the first head plane (PH1), each recess surface (74) is located outside the first imaginary circle (C1).

A cutting head (20) rotatable about a head axis (AH) in a direction of cutting rotation (RC), the head axis (AH) establishing an axial forward direction (DF) and an axial rearward direction (DR), comprising:

• a cap portion (22) having N cutting portions (26) circumferentially alternating with N head flutes (28), and a cap base surface (30) facing in the axial rearward direction (DR);
• and
• a mounting protuberance (24) joined to the cap portion (22), extending axially rearwardly from the cap base surface (30), the mounting protuberance (24) having:
• a mounting end surface (36) distal from the cap portion (22), facing in the axial rearward direction (DR), and
• N circumferentially spaced apart engagement portions (34), each engagement portion (34) including a radially outward facing clamping surface (38), and a torque transmission surface (40) facing opposite the direction of cutting rotation (RC),
• wherein:
• N is an integer equal to 3;
• and
• in a cross-section taken in a first head plane (PH1) perpendicular to the head axis (AH), intersecting the N engagement portions (34) and passing through the N clamping surfaces (38) and the N torque transmission surfaces (40):
• a first imaginary circle (C1) centered about the head axis (AH) and having a first diameter (D1) circumscribes the N clamping surfaces (38),
• a second imaginary circle (C2) centered about the head axis (AH) and having a second diameter (D2), is defined by N radially outermost torque points (NTO) of the N torque transmission surfaces (40),
• the second diameter (D2) is greater than ninety percent and less than one hundred percent of the first diameter (D1), and
• the N torque transmission surfaces (40) define an imaginary torque triangle (TT).