The jet deflection phenomenon is one of the main causes for the larger workpiece final diameter respect to the ideal target diameter in Abrasive Waterjet Turning (AWJT). Hence, the predetermination of the final workpiece diameter necessitates measuring the jet deflection. The aim of the present work is to develop a novel on-line measurement methodology of the 3D deflection of the jet in AWJT by the contemporary use of two cameras and a dedicated image processing routine. The selected variable machining process parameters were feed rate (Vf), depth of cut (DOC) and the rotational direction of the workpiece. An empirical model was developed for predicting the workpiece final diameter accuracy on Al 2024 alloy based on the jet deflection and including the effect of the jet divergence. The obtained results form the base for a new type of AWJT modelling, on-line monitoring and closed-loop control and could be a first step to make the DOC a handier process parameter, as it happens in standard turning.