For a generalized helical end mill, this paper presents a frequency domain force modelconsidering the ploughing as well as the shearing mechanisms. The differential chip load and the corresponding cutting forces are first formulated through differential geometry for a general helical cutting edge. The differential cutting force is assumed to be a linear function of the chip load with a proportional shearing force and a constant ploughing force. The total milling force in the angle domain is subsequently composed through convolution integration and analyzed by Fourier analysis. The frequency domain model has the parameters of a general milling process all integrated in a single framework with their roles clearly defined so that Fourier coefficients of the milling force can be obtained for any analytically definable helical cutter. Applications are illustrated for three common helical cutters: the cylindrical, taper, and ball end mills. Furthermore, as an inverse application, a linear algebraic equation is formulated for the identification of six cutting constants from the average forces of two slot milling tests. Demonstration and verification of the milling force model as well as the identification of cutting constants are carried out through experiments with three types of milling cutters.