Abstract: In order to overcome the problems of large off-axis amount,large vector height difference and low surface accuracy faced by traditional machining technology when machining the off-axis parabolic mirror with equal thickness,a machining method based on slow tool servo technology was proposed,which is applicable to large off-axis amount,large vector height difference and high machining accuracy. The method adopted the coordinate translation strategy,which effectively solved the problem of large off-axis amount existing in the off-axis paraboloid; a new angular coordinate rotation method was used to ensure that the vector height difference at the far and near axis ends of the off-axis paraboloid is close to 0,so as to achieve the goal of equal thickness. In addition,the method of equal angle-equal arc length was used to discretize the contact points between the tool and the machined surface,and the tool radius compensation in Z direction was carried out for these contact points to generate the machining path,making the machining accuracy higher. RSA6061 aluminum alloy off-axis parabolic mirror parts (diameter of 25.4 mm,radius of curvature of 50.8 mm,off-axis angle of 90°) were processed by the processing method proposed. An equal thickness off-axis parabolic aluminum alloy mirror with surface accuracy of RMS of 0.124λ(λ= 632.8 nm) and surface roughness of Sa of 1.952 nm has been successfully fabricated. The machining method not only makes the machining process more concise,but also helps to improve the machining quality of the workpiece.

Key words: ultra-precision turning, off-axis paraboloid with equal thickness, slow tool servo, trajectory optimization