Offset fabrication of off-axis aspherical surfaces with large off-axis amounts by slow tool servo single-point diamond turning

Off-axis aspherical mirrors are widely used in optical systems and precision measuring instruments, whereas off-axis aspherical mirrors with large sizes and off-axis are used in large optical systems such as astronomical telescopes and radio telescopes. However, if the off-axis amount of an off-axis aspherical mirror exceeds the capability of the machine tool, traditional rotary-turning machining methods are not applicable, and advanced computerized numerical control (CNC) machining methods, such as the slow-tool-servo method, must be implemented. This article proposes a non-conventional offset (NCO) fabrication method based on slow-tool-servo single-point diamond turning for machining off-axis aspherical surfaces with large off-axis amounts. This method is theoretically applicable to the machining of off-axis aspherical surfaces with any off-axis amount. NCO fabrication is a simpler and more efficient path-planning solution for machining individual off-axis parabolic surfaces. In addition, corresponding solutions for other types of aspherical surfaces are proposed using the NCO method. The turning depths of workpieces with different off-axis amounts at the same machining position are analyzed and compared. A specific measurement scheme for the NCO method is presented, and the experimental results indicate that the PV and RMS form errors are 0.658 µm and 60 nm, respectively. This work demonstrates that the NCO method can effectively deal with the machining challenges of off-axis aspherical structures with large off-axis amounts.