Method of spin forming and part made thereof

A method of cold forming a capped cylinder with a generally smooth surface on the interior thereof and geometrically spaced torsional engagement radial projections on the exterior surface of said capped cylinder, said method comprising the steps of:

• striking a generally flat blank to form a drawn part having a generally flat capped portion, a generally right angle cylindrical portion adjacent an open end of said capped cylinder and a skirt joining said flat capped portion and said right angle cylindrical portion;
• piercing a central aperture in said capped portion;
• piercing said capped portion to provide a plurality of fastener attachment apertures which are located around the periphery of and are spaced from said central aperture;
• further processing said drawn part by placing it in a spinner machine having a rotatively mounted die with a cylindrical die cavity having a first diameter with a series of radial die projections extending to a second diameter which is greater than said first diameter and having a driven mandrel without any teeth and having a rotational axis, with the mandrel having a lower shoulder, an upper shoulder, and a top end portion which is generally flat;
• inserting the mandrel into the open end of said capped cylinder for supporting same, with the top end portion of said mandrel supporting the generally flat portion of the capped cylinder;
• and
• rotating said driven mandrel and axially and laterally moving said die and said mandrel with respect to one another, said mandrel engaging and plastically deforming the interior surface of said drawn part cylindrical portion by forcing the cylindrical side portion of the capped cylinder radially outwardly into said series of radial die projections of said die cavity to cold form said geometrically spaced torsional engagement radial projections on said exterior surface of said cylindrical portion of said capped cylinder while maintaining the interior surface thereof generally smooth.