Tolerance analysis of cradle-type double rotary table using the local parallel dimension chain method

As one of the pivotal components of computer numerical control (CNC) machine tools, the CNC rotary table plays a crucial role in machining workpieces. The accumulated assembly error not only compromises the machining accuracy of the workpiece but also diminishes the service life of the CNC machine tool due to vibrations arising from assembly clearances. Addressing this issue, the study focuses on the cradle-type double rotary table of a five-axis machining center and investigates the structural composition and assembly relationships of the rotary table. An error transmission model for the cradle-type double rotary table based on the Jacobian-Torsor theory is also constructed. Furthermore, a local parallel dimension chain method is introduced to simplify the error transmission dimension chain of the cradle-type double rotary table, and Monte Carlo simulation is employed to evaluate the cumulative assembly error. Finally, the coaxiality error of the swing axis and the table error of the rotary axis’ worktable were respectively calculated, followed by a discussion of the results. This method provides comprehensive guidance for the error assessment and structural optimization of five-axis machining centers.