Purpose: This paper is focused on the optimal cutting parameters design of rough cutting processes in side milling for SKD61 tool steels.Design/methodology/approach: The fuzzy logics can be a proper basis to perform the optimization procedure with complicated multiple performance characteristics in this paper. Using this approach combined with the grey-relational analysis, the design algorithm is transformed into optimization of a single and simple grey-fuzzy reasoning grade rather than multiple performance characteristics. The Taguch method is also adopted to search for an optimal combination of cutting parameters for this rough cutting process in side milling.Findings: The improvement of tool life and metal removal rate from the initial cutting parameters to the optimal cutting parameters are 54% and 9.7%. Hence, this reveals that the proposed approach in this study can effectively improve the cutting performance.Research limitations/implications: In this paper only four cutting parameters are taken into consideration. Many other parameters such as tool geometric shape are not applied to this study.Practical implications: It is believed that this optimal result can be applied to practical processes to effectively reduce manufacturing cost and greatly enhance manufacturing efficiency.Originality/value: A systematic and effective optimization method is presented in this paper. Using this method can effectively acquire an optimal combination of the cutting parameters.