Using the basic model of double edge cutting, the minimum value of the total shear area produced by the two cutting edges is calculated to determine the chip flow direction: shearing takes place in the corresponding direction of chip flow to make the shear area minimum under specific cutting parameters with sharp corner tools. The chip flow angle can be obtained using the expression of the variation of the shear area with the chip flow angle. In this study, RATIO is defined as the ratio of the main to the minor cutting edge length engaged in cutting and is set variable on the basis of the constant equivalent cutting area. The chip flow angle corresponding to different values of RATIO predicted by the current model shows good correlation with the experimental measurement and FEM simulation results for various cutting conditions. An investigation of the effects of RATIO on the chip flow angle has been made under various cutting conditions and it is demonstrated that RATIO has a significant influence on the chip flow angle.