Replaceable cutting head having back-tapered conical external thread and rotary cutting tool

A rotary cutting tool (20) having a longitudinal axis (L) and extending in a forward (DF) to rearward direction (DR), comprising:

• a tool holder (24) having a holder longitudinal axis (C) and comprising a female coupling member (68) having an internal thread (72) extending rearwardly from a holder forward surface (70), the holder forward surface (70) extending transversely with respect to the holder longitudinal axis (C);
• and
• a replaceable cutting head (22) threadingly engaged to the tool holder (24), the replaceable cutting head (22) having a head longitudinal axis (A) extending in a forward (DF) to rearward direction (DR), and comprising
• a forward portion forming a cutting portion (26);
• and
• a rearward portion forming a mounting portion (28), the mounting portion (28) comprising a male coupling member (38) having an external thread (42) and protruding rearwardly from a head base surface (40), the head base surface (40) extending transversely with respect to the head longitudinal axis (A), and defining a boundary between the cutting portion (26) and the mounting portion (28), wherein:
• the external thread (42) comprises an external thread ridge (44) extending helically about an external thread axis (B) and comprising forward and rearward external flank surfaces (46, 48) and an external top surface (50) extending therebetween;
• the forward and rearward external flank surfaces (46, 48) generally face in opposite axial directions (DF, DR) and delimit a helical external thread groove (52) that comprises an external bottom surface (54);
• and
• the external thread (42) of the male coupling member (38) is a back-tapered conical thread having at least one thread diameter (d1, d2) which increases in the rearward direction (DR);
• wherein:
• the rotary cutting tool (20) is adjustable between:
• a released position in which the internal and external threads (42, 72) are not threadingly engaged to one another, and
• a locked position in which the male coupling member (38) is removably retained in the female coupling member (68) with the internal and external threads (42, 72) threadingly engaged to one another;
• and
• the frictional engagement between the external thread (42) and the internal thread (72) increases in a direction from a forwardmost turn of the external thread (42) towards the rearmost turn of the external thread (42).

A rotary cutting tool (20) having a longitudinal axis (L) and extending in a forward (DF) to rearward direction (DR), comprising:

• a replaceable cutting head (22) having a head longitudinal axis (A) extending in said forward (DF) to rearward direction (DR), and comprising:
• a forward portion forming a cutting portion (26);
• and
• a rearward portion forming a mounting portion (28), the mounting portion (28) comprising a male coupling member (38) having an external thread (42) and protruding rearwardly from a head base surface (40), the head base surface (40) extending transversely with respect to the head longitudinal axis (A), and defining a boundary between the cutting portion (26) and the mounting portion (28), wherein:
• the external thread (42) comprises an external thread ridge (44) extending helically about an external thread axis (B) and comprising forward and rearward external flank surfaces (46, 48) and an external top surface (50) extending therebetween;
• the forward and rearward external flank surfaces (46, 48) generally face in opposite axial directions (DF, DR) and delimit a helical external thread groove (52) that comprises an external bottom surface (54);
• and
• the external thread (42) of the male coupling member (38) is a back-tapered conical thread having at least one thread diameter (d1, d2) which increases in the rearward direction (DR);
• and
• a tool holder (24) having a holder longitudinal axis (C) and comprising:
• a female coupling member (68) having an internal thread (72) extending rearwardly from a holder forward surface (70), the holder forward surface (70) extending transversely with respect to the holder longitudinal axis (C);
• wherein:
• the internal thread (72) comprises an internal thread ridge (74), extending helically about an internal thread axis (D), and comprising forward and rearward internal flank surfaces (76, 78) and an internal top surface (80) extending therebetween;
• and
• the forward and rearward internal flank surfaces (76, 78) generally face in opposite axial directions (DF, DR) and delimit a helical internal thread groove (82) that comprises an internal bottom surface (84);
• and
• wherein:
• the rotary cutting tool (20) is adjustable between:
• a released position in which the internal and external threads (42, 72) are not threadingly engaged to one another, and
• a locked position in which the male coupling member (38) is removably retained in the female coupling member (68) with the internal and external threads (42, 72) threadingly engaged to one another;
• and
• in the locked position:
• the forward internal flank surface (76) is spaced apart from the rearward external flank surface (48) by a rearward flank distance (D1);
• the internal top surface (80) is spaced apart from the external bottom surface (54) by an upper distance (D2);
• the internal bottom surface (84) is spaced apart from the external top surface (50) by a lower distance (D3);
• and
• the rearward flank, upper and lower distances (D1, D2, D3) all decrease in the rearward direction (DR).