Rotary cutting tool with internal coolant passage

A rotary cutting tool, comprising:

• a cutting insert;
• a tool body including a pocket portion for holding the cutting insert and a chip flute portion having a plurality of helical chip flutes;
• and
• a first internal coolant passage formed in the chip flute portion, wherein the first internal coolant passage has a twisted geometry and has a central longitudinal axis which lies within the first internal coolant passage and which is generally collinear with the central longitudinal axis of the rotary cutting tool,
• wherein the first internal coolant passage is generally rectangular with two rounded end cusps and two substantially planar side walls,
• wherein the first internal coolant passage further includes a see-through central portion which defines an unobstructed linear coolant path when viewed from the first end of the cutting tool along the central longitudinal axis of the rotary cutting tool, and
• wherein the cutting insert includes a base surface with a coolant opening in fluid communication with the first internal coolant passage, and wherein the coolant opening has a substantially identical cross-sectional shape as the first internal coolant channel.