Abstract Micro mechanical machining operations can fabricate miniaturized components from a wide range of engineering materials; however, there are several challenges during the operations that can cause dimensional inaccuracies and low productivity. In order to select optimal machining parameters, the material removal behavior during micro machining operations needs to be understood and implemented in models. The presence of the tool edge radius in micro machining, which is comparable in size to the uncut chip thickness, introduces a minimum uncut chip thickness (MUCT) under which the material is not removed but ploughed, resulting in increased machining forces that affect the surface integrity of the workpiece. This paper investigates the MUCT of rounded-edge tools. Analytical models based on identifying the stagnant point of the workpiece material during the machining have been proposed. Based on the models, the MUCT is found to be functions of the edge radius and friction coefficient, which is dependent on the tool geometry and properties of the workpiece material. The necessary parameters for the model are obtained experimentally from orthogonal cutting tests using a rounded-edge tool. The minimum uncut chip thickness (MUCT) is then verified with experimental tests using an aluminum workpiece.