Rotary damper manufacturing method and rotary damper

A rotary damper manufacturing method,

• a rotary damper including a housing body having a cylindrical inner chamber liquid-tightly housing fluid and a fixed vane formed in a wall shape in the inner chamber and blocking a flow of the fluid in a circumferential direction, a rotor having, at an outer peripheral portion of a shaft, a movable vane turning so as to push the fluid to a fixed vane side while partitioning the inner chamber, and a lid provided on the housing body to liquid-tightly close the inner chamber,
• the lid having an annular lid-side fitting portion to be fitted into or onto an inner peripheral portion or an outer peripheral portion of the housing body,
• the housing body having an annular housing-side fitting portion to be fitted onto or into the lid-side fitting portion,
• one of the lid-side fitting portion or the housing-side fitting portion being made of a material less plastically deformable than that of the other fitting portion, and
• the one fitting portion being formed with a recessed portion which is recessed to a side away from the other fitting portion and is formed continuously or intermittently along the circumferential direction, the rotary damper manufacturing method comprising:
• an indentation formation step of applying pressure over an entire circumference of the other fitting portion more plastically deformable than the one fitting portion in a state of the lid-side fitting portion and the housing-side fitting portion being fitted in each other to plastically deform part of the other fitting portion in a radial direction and cause the part of the other fitting portion to enter the recessed portion, thereby forming an indentation.