Method for forming a dual threaded die

A method for forming a dual threaded die with a forming surface having a fine thread forming structure at a different pitch angle than a coarse thread forming structure, the die suited to roll form a screw having a dual threaded form including a coarse thread and a fine thread at different pitch angles, the method including the steps of:

• forming an EDM electrode to have a face with a geometry including:
• a plurality of troughs and tips matching a cylindrical projection of a coarse thread geometry of the screw;
• a plurality of grooves cutting across each tip, the grooves matching a fine thread geometry of the screw;
• the grooves angled relative to the tips by an angle matching a difference between the pitch angle of the coarse thread and the pitch angle of the fine thread;
• locating the EDM electrode face adjacent to the forming surface of the die;
• shaping the forming surface of the die by electric discharge machining via the EDM electrode;
• wherein said forming step includes grinding the troughs into the face of the EDM electrode to match the coarse thread geometry of the screw;
• wherein said grinding includes contacting the face of the EDM electrode with a rotating grinding drum having grinding ribs thereon;
• wherein said grinding includes contacting the face of the EDM electrode with a rotating grinding drum having grinding ribs thereon;
• wherein said grinding includes the grinding ribs oriented in parallel circumferential rows, each extending around a circumference of the drum;
• and
• wherein said grinding includes a central axis of the drum being angled relative to side edges of the EDM electrode to match the pitch angle of the coarse thread of the screw.