Surface cutting

Patent Pending PROBLEM TO BE SOLVED: To provide a method of cutting an axisymmetric diffraction curved surface of a Fresnel lens made of a fragile material such as an optical crystal of a different type and a glass, easily, at a low machining cost, and with high precision. ; SOLUTION: The method comprises a step in which while a minute sword-shaped cutting tool 11 having a pointed tip is driven on the workpiece 1 having a rotation axis along a constant locus, straight line enveloping is carried out by uniaxial (Z) straight line motion and triaxial simultaneous control of a B axis in addition to two axes (XZ), and a discontinuous diffraction curved surface is formed in a surface of the rotating workpiece 1 by transfer and enveloping of a cutting edge of the sword-shaped cutting tool 11.