From 2017 Dpreview and Imaging Resources.
From Imaging Resources:
Takumi Toshi Saito demonstrates the process of hand-shaping a master template used to make the diamond-grit grinding tools for lenses. The piece in his hand is a heavy polishing jig, this particular one weighing around 30 pounds (15kg), with diamond grit on the inside. The little plugs on the jig that he's grinding define the surface that the final tool will have. They have to be ground to within a tolerance of 30 nanometers (30 millionths of a millimeter). The tool he's using to do the hand-grinding doesn't exactly match the final target profile; Saito-san tweaks and adjusts the shape of the forming jig by adjusting the pressure as he slides the grinding tool over the jig. Normally, the jig is rotating while he does this, requiring a complex dance of pressure, angle, distance and timing. It was mind-boggling to us that someone could hand-grind something to tolerances in the millionths of millimeters.
From Imaging Resources:
Takumi Toshi Saito demonstrates the process of hand-shaping a master template used to make the diamond-grit grinding tools for lenses. The piece in his hand is a heavy polishing jig, this particular one weighing around 30 pounds (15kg), with diamond grit on the inside. The little plugs on the jig that he's grinding define the surface that the final tool will have. They have to be ground to within a tolerance of 30 nanometers (30 millionths of a millimeter). The tool he's using to do the hand-grinding doesn't exactly match the final target profile; Saito-san tweaks and adjusts the shape of the forming jig by adjusting the pressure as he slides the grinding tool over the jig. Normally, the jig is rotating while he does this, requiring a complex dance of pressure, angle, distance and timing. It was mind-boggling to us that someone could hand-grind something to tolerances in the millionths of millimeters.