A ring-shaped mold of the split mold type constructed by assembling into an annular shape a plurality of sectorial separate blocks formed by cutting a ring-shaped workpiece haveing a mold surface on the annular circumference thereof, and the method and apparatus for making the same are disclosed. Sector lines interfacing adjoining the separate blocks on the mold surface intersect the circumference of the ring-shaped mold at angles not perpendicular to said circumference.
