Patent ID: 8141227

Claim:
A method of making a cylinder assembly comprising an outer cylinder and a tubular support member disposed around and in overlapping relation with the outer cylinder, the outer cylinder and the tubular support member being joined together, the method comprising: forming an overlapping part by fitting the tubular support member over the outer cylinder; inserting a die device including a die cavity into the outer cylinder so that the die cavity faces an outer cylinder inner surface of the overlapping part; preparing a punch device including a stepped forward end portion, the stepped forward end portion comprising a cylindrical base portion, a tip portion having a tip end and a base portion side opposite the tip end, the tip portion being smaller in diameter than the base portion, and a curved surface portion connecting the base portion and the tip portion, the curved surface portion being concave inwardly of the stepped forward end portion, the cylindrical base portion smoothly merging into the tip portion through the curved surface portion, the tip portion extending from the base portion side of the tip portion to the tip end without the diameter of the tip portion being enlarged; and drawing the overlapping part by moving the punch device from a radially outer side of the tubular support member toward the die cavity of the die device until the curved surface portion of the punch device enters the tubular support member, thereby joining together the outer cylinder and the tubular support member, wherein the jointed overlapping part of the outer cylinder and the tubular support member are in contact with each other in a cup-like shape such that an angle of a tangent to the side wall inner surface of a recess of the outer cylinder, which is located forward relative to tubular support member in the drawing direction, is 90 degrees or less.