This paper presents a study of warped surfaces machining with ball end milling. A specific model based on the classical stability lobe theory was used and improved with important aspects. The non-linear effect of radial allowance on the contact angle was integrated by an original averaging method. The cutting coefficients are updated in order to follow effective radius and cutting velocity. An original experimental procedure was developed in order to compute the cutting coefficient for various inclined surfaces. More complete experimental analysis was conducted in order to study the effect of machining parameters on the stability of inclined surface milling. The comparison between experiment and simulation shows good correlation for the prediction of stable cutting condition.