Manufacturing of parts made out of difficult-to-cut materials presents many challenges. Reduced productivity and increased cost due to low machinability and tool life are main problems in these applications. Turn-milling may offer important advantages in solving these problems. Turn-milling combines conventional turning and milling processes providing lower cutting temperatures, higher process flexibility and productivity. Turn-milling processes have additional parameters one of which is the eccentricity between the tool and workpiece axes. The objective of this study is to develop a process model for eccentricity effects on orthogonal turn-milling operation. Process model includes chip geometry and cutting force calculations. In addition, effect of eccentricity on tool wear is also investigated in this paper. Although intermitted characteristics of turn-milling provide benefits such as lower cutting temperature and longer tool life, there are some drawbacks which have to be taken into consideration. In this direction, analytical definitions related to surface quality such as circularity, surface roughness and cusp height under the effect of eccentricity are also investigated. Experiments were carried out on a multi tasking CNC machine tool. Analytical solutions and experimental results are compared to verify the process model. (C) 2014 Published by Elsevier B.V.