Method for producing molding die for synthetic resin lens barrel having a helicoid and for producing the lens barrel

摘要

A method for producing a male helicoid molding die which is adapted to manufacture an inner barrel having a male helicoid, and for producing a female helicoid molding die which is adapted to manufacture an outer barrel having a female helicoid which can engage with said male helicoid of the inner barrel. The method includes the steps of firstly, setting an included angle of trapezoidal threads of the male helicoid to be identical to an included angle of trapezoidal grooves of the female helicoid in a section perpendicular to a direction of an extension of the threads and preparing a cutting tool having an angle identical to the set angle. Secondly, the male helicoid molding die is machined to form a helicoid portion thereof using the cutting tool. Next, an electric spark machining electrode is prepared having a helicoid portion whose shape is identical to a shape of the helicoid portion of the male helicoid molding die, by a mechanical cutting operation, using the cutting tool. Then a helicoid portion of the female helicoid molding die is formed by electric spark machining using the electric spark machining electrode.