Abstract: That the function of machine tools is determined by three elements of workpiece shapes is analysed. A theory that divides reconfigurable machine tools into modulus according to reconfigurable grain size of three elements modulus is put forward. The cost of reconfigurable machine tools based on the theory will be lowest easily. The theory lays a better foundation for researching、designing and building reconfigurable machine tools. The application of the theory for reconfigurable lower speed wire electrical discharge machine tools( LS-WEDM) is studied.

Key words: Grain size, LS-WEDM, Machine tools error, Modulus, Reconfigurable manufacturing system