PURPOSE: To improve the limit helix angle by forming the surface of a raw material for twisting process in a waveform surface with projected and recessed lines extending from one end to the other end, or in a coarse surface facing from one end to the other end, and applying a twisting process to the raw material.
CONSTITUTION: A waveform surface 3 is formed on the surface of a raw material 2 for twisting process. The waveform surface 3 is formed of plural projected and recessed lines 3a and 3b extending straightly from one end to the other end, on the surface of the intermediate arm 21 expect the hollow swellings 2a and 2a at both ends, and it is formed on the whole surface of the intermediate arm 21. After that, by using this raw material, a twisting process is applied by chucking both ends so as to form a twisted member 5. In this case, the deformation absorbing force of the raw material 2 is increased by the function of the waveform surface 3, and a generation of crack and a deterioration of quality can be prevented, and the raw material 2 can be processed in a severe twisting condition.
TAKAMI YUICHI
YOKOYAMA MASAO
