Flexible parts such as turbine blade, blisk and monolithic components are widely used in the aeronautical industry, and high Speed Machining (HSM) technology is used to increase productivity and reduce production costs. Chatter is an undesirable phenomenon in high speed machining processes because of deteriorative surface finish, early cutting tool failure and unexpected machine tool damage. It can be avoided in higher speed milling processes if stability lobes is determined. In this paper, a non-linear regenerative force model is applied to a bull-nose tool geometry in order to obtain the machine operation stability lobes. An analytical-experimental method is proposed to obtain the stability lobes during high speed milling flexible parts with bull-nose end mills. The method is calculated and validated.