WORKING METHOD OF THREAD CUTTING PART

PURPOSE:To form a spiral projecting line or groove on the side wall of a work with good working performance and workability by inserting the work in a master mold of a bottomed cylindrical shape and, fitting a coil-like guide member between the work and the master mold, and press inserting an inside mold into the master mold. CONSTITUTION:A work 13 is inserted into a master mold of a bottomed cylindrical shape formed of the base 11 and a cylindrical member and a coil-shaped guide member 14 is fitted between the work 13 and a member 12 forming a part of the master mold. A pressure shown by an arrow P is exerted on an inside mold 15 from the outside to push the mold 5 along the member 12. Then the side wall part of the work 13 is laterally bulged and deformed while said part is compressed to conform to the shape of the member 14 at the same instant when the internal pressure in the work 13 is increased. The member 14 consists preliminarily of a piece of continuous bar body like a coil spring and therefore the projecting line or groove formed on the side wall part of the work 13 is also continuously spiral.