Off-axis free surface turning method by actively changing spindle rotating speed

The invention relates to an off-axis free surface turning method by actively changing spindle rotating speed, and belongs to an ultra-precision cutting and complex surface optical part cutting method. The method comprises the following steps of: performing off-axis mounting of two or more free surface workpieces in an equally spaced mode, wherein the off-axis mounting position and posture are adjustable; and actively changing the spindle rotating speed according to a coordinate position of a contact point of a diamond cutter so as to ensure consistency of the cutting speed on the machined surface. The invention has the advantages that: the dependence of the cutting speed on the contact point position of the diamond cutter is decoupled, a free surface is formed due to off-axis turning, and uniform and consistent quality of the machined surface can be obtained; moreover, the method is simple and convenient, and is easy to implement.