Torsional stiffness of a rotary feed drive system not only has great influence on the rotary positioning accuracy, but also affects the system dynamic characteristics. This paper proposes an estimating approach for the torsional stiffness of typical transmission chains in rotary feed drive tables. Firstly, a general analytical torsional stiffness model is presented, taking torsional stiffness of shafts and meshing stiffness between gear teeth into account. Then, general expressions of coefficients in the model relating adjacent angular displacements in the typical transmission chains are derived under static equilibrium condition. Moreover, a torsional stiffness test experiment is conducted for a rotary drive table and the stiffness estimation algorithm is presented. To verify the validity of the proposed approach, comparisons among the traditional model, finite element model and the proposed one are made. The results show that the stiffness value obtained from traditional model is bigger than the presented analytical model. The finite element analysis and experimental results indicate the analytical model is valid and more accurate than the traditional ones. This work provides an effective and general way to estimate the torsional stiffness of typical transmissions employed in rotary table of machine tools during the system design and characteristic analysis process.