WORKING METHOD OF METAL MOLD FOR FRESNEL LENS, TOOL TO BE USED THEREFOR, AND METAL MOLD AND FRESNEL LENS WORKED BY THIS WORKING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a working method of a metal mold capable of preventing lowering of tool longevity due to chipping and giving an additional value to a fresnel lens. SOLUTION: This is the working method of the metal mold 20 for the Fresnel lens to work a fresnel molding groove 12 having wall surfaces 13, 14 respectively corresponding to a lens surface 31 and a non-lens surface 32 of the Fresnel lens 30 into a metal mold original board, wherein one crest line 5 continued to a knife edge 4 is formed as a cutting blade, and a tool 1 with a cutout part 7 connecting the one crest line 5 and the other crest line 6 to each other formed on it is used for the knife edge 4. The tool 1 is delivered to the metal mold original board 10 with the cutting blade 5 on its head so that the wall surface 14 corresponding to the non-lens surface of the fresnel molding groove 12 is gradually cut from it supper end by the cutout part 7 while giving relative rotating motion around a central line AX of the metal mold between the tool 1 and the metal mold original board 10. An irregular cutting mark 15 is formed by the cutout part 7 on the wall surface 14 corresponding to the non-lens surface.