How to diamond turn an elliptic half-shell?

In this research note we are introducing a new slow slide servo (SSS) turning technique which enables fast diamond machining of deep aspheric surfaces which otherwise can only be machined by ball-end milling, if at all. The key idea is to execute the servo motion not only parallel to the axis of rotation, which is the standard mode implemented in commercial SSS software, but in a plane incorporating both directions parallel and perpendicular to the rotational axis. In this way the risk of collisions in non-circular turning between the tool shaft and the machined surface can be reduced significantly. Moreover, when a 180° contour is machined, the acceleration of the servo slide will not increase indefinitely. After a review of the standard SSS turning technique we will outline the generalized SSS concept and demonstrate its applicability by diamond turning of an elliptic half-shell on a commercial diamond turning lathe.