This paper presents a new predictive model for chip back-flow angle in machining with restricted contact grooved tools. This model is derived from the recently established universal slip-line model for machining with restricted contact cut-away tools. A comprehensive definition of the chip back-flow angle is first developed, and based on this, a quantitative analysis of the effect of chip back-flow is presented for the given set of cutting conditions, tool geometry and variable tool-chip interfacial stress state. This model also predicts cutting forces, chip thickness ratio and chip up-curl radius. A full experimental validation of the predictive model involving the use of high speed filming techniques is then presented for chip back-flow angle and this validation provides a range of feasible/prevalent tool-chip interfacial frictional conditions for a given set of input conditions.