Patent ID: 7086152

Claim:
A method of forming a peripheral tubular body surface of an engine piston defined about and along a longitudinal axis thereof with a helical oil supply surface groove extending over at least part of its length, the method comprising: forming the piston body with an oversized, roughly finished wall defining a primary surface spaced from the longitudinal axis; rotating the piston body about the longitudinal axis; relative to a cutting tool, during said rotation, cutting into the primary surface to define a helical groove advanced longitudinally with such pitch that consecutive turns form therebetween a helical ridge having corresponding consecutive turns; for each ridge turn between said defined groove turns, removing the piston body material to form a plateau of predetermined flattened shape in the longitudinal direction defining a final outer sur&ce boundary of the tubular body surface of the engine piston, wherein the piston body material is removed by planning and wherin proove cutting and ridge planning is effected simultaneously.