Complex sentence: When the tips are blunt, they may be removed, rotated (indexed) and replaced to present a fresh, sharp face to the workpiece, this increases the life of the tip and thus their economical cutting life.
Split into simpler sentences: When the tips are blunt, they may be removed, rotated (indexed) and replaced to present a fresh, sharp face to the workpiece. This increases the life of the tip and thus their economical cutting life.