A manufacturing method of a bending tube in which two types of nodal rings, which are first nodal rings and second nodal rings, are alternately coupled with each other in a longitudinal direction to allow each of them to rotate, the method comprising:
- forming a predetermined number of first nodal-ring preliminary bodies in a first plate-like member, each of the first nodal-ring preliminary bodies having a strip-like shape and being configured to be formed into a corresponding one of the first nodal rings by circularizing, one or both ends each first nodal ring preliminary body in a circumferential direction of the bending tube being coupled with an edge of the first plate-like member through a first edge crosspiece portion in the first plate-like member, and first gaps being formed between the first nodal ring preliminary bodies in the longitudinal direction in the first plate-like member;
- forming a predetermined number of second nodal-ring preliminary bodies in a second plate-like member, the second plate-like member being different from the first plate-like member and being a separate member from the first plate-like member, each of the second nodal ring preliminary bodies having a strip-like shape and being configured to be formed into a corresponding one of the second nodal rings by circularizing, one or both ends each second nodal ring preliminary body in a circumferential direction being coupled with an edge of the second plate-like member through a second edge crosspiece portion in the second plate-like member, and second gaps being formed between the second nodal ring preliminary bodies in the longitudinal direction in the second plate-like member;
- forming a protruding portion on one of a first coupling portion provided to each first nodal ring preliminary body and a second coupling portion provided to each second nodal ring preliminary body by burring processing;
- forming a through hole, which engages with the protruding portion, in the other of each first coupling portion and each second coupling portion;
- overlapping the first plate-like member with the second plate-like member in a state that each of the second nodal ring preliminary bodies is arranged in a corresponding one of the first gaps of the first plate-like member and each of the first nodal ring preliminary bodies is arranged in a corresponding one of the second gaps of the second plate-like member, and thereby engaging the protruding portions with the through holes and coupling the first nodal ring preliminary bodies with the second nodal ring preliminary bodies;
- disconnecting the first nodal ring preliminary bodies from the edge of the first plate-like member at the first edge crosspiece portion and disconnecting the second nodal ring preliminary bodies from the edge of the second plate-like member at the second edge crosspiece portion;
- and
- forming the first nodal ring preliminary bodies and the second nodal ring preliminary bodies into circular shapes by bending processing after coupling the first nodal ring preliminary bodies with the second nodal ring preliminary bodies, and joining and connecting part or all of both ends of each first nodal ring preliminary body in the circumferential direction and joining and connecting part or all of both ends of each second nodal ring preliminary body in the circumferential direction.