Tube cutting apparatus and tube manufacturing method

A tube cutting apparatus comprising:

• an annular outer blade having an inner peripheral surface which contacts an entire circumference of an outer periphery of a tube to be cut so as to cover a predetermined axial range of the outer periphery;
• a disc-shaped inner blade which is retained inside the tube with a central axis thereof extending parallel with an axis of the tube and has at least one side surface positioned within the tube so as to substantially coincide with a side surface of the outer blade in an axial direction of the tube;
• and
• an inner blade driving mechanism having a ring gear positioned outside the tube coaxially with the tube and a planetary gear having external teeth meshing with internal teeth of the ring gear, wherein:
• the inner blade driving mechanism is configured to move the planetary gear along a pitch circle of the ring gear and has a first shaft serving as a central axis of the planetary gear and a second shaft extending parallel with the first shaft and supporting the inner blade for rotation, the second shaft being rotatably supported at a predetermined position which is different from a position of the first shaft in a plane perpendicular to the first shaft;
• and
• the inner blade has a peripheral surface which is caused to become exposed exteriorly of the tube from the inside of the tube, thereby cutting the tube cooperatively with the outer blade.