Patent ID: 7594332

Claim:
A method of making a cylindrical bearing member on whose inner circumferential surface a plurality of blind grooves for oil reservoirs are provided, comprising the steps of extrusion molding a circular column-shaped crude material into a hollow cylindrical member with a thin bottom at one end and an open end at the other, the hollow member including a straight cylindrical outer surface from said thin bottom to said open end, and an intermediate tapered inner circumferential surface in a straight-walled conical form, having a large diameter at its open end, and a gradually reduced diameter terminating in a small diameter towards said bottom; placing said hollow member in a die having a straight cylindrical bore longer than said hollow member, and pushing a groove forming die pin including a plurality of groove forming protrusions with an outer perimeter less than said large diameter and greater than said small diameter, from said open end toward said bottom to form a cylindrical member with a thin bottom provided with a plurality of grooves on the inner circumferential surface, each of said grooves having a closed terminal adjacent said bottom wall and an open terminal in said tapered inner circumferential surface adjacent said open end, removing said die pin; and thereafter closing groove open terminals by straightening said tapered inner circumferential surface into a hollow cylindrical form of work-hardened ring having an internal diameter equal to said small diameter beyond said open terminals to close said terminals, and then removing the thin bottom from said straightened cylindrical member.