Abstract: Aiming at the problem that the accuracy design index of the machine tool is difficult to be determined reasonably in the geometric precision design process of CNC machine tools, a method for solving the allowable range of the pose error of the tool relative to the worktable based on the tolerances of the workpiece to be processed is proposed. Firstly, the constraint model between the single tolerance item of the workpiece and the pose error of machine tool is established. That is to say, in order to satisfy the requirement of a single tolerance item, the allowable range of the pose error can be determined. Secondly, the required accuracy design index of the machine tool can be obtained by calculating the intersection of every range corresponding to every single tolerance item, which can then be used for tolerance allocation process. The solution methods of the common tolerance items are derived, and the machining test piece is selected as an example to show the effectiveness of the proposed method.

Key words: machine tool, geometric accuracy, accuracy design, design index, tolerance