The workpiece dynamics affect stability in machining of flexible parts. However, it is not a straightforward task to include it in the analysis since the workpiece dynamics continuously change due to mass removal and variation of the cutter contact. In this paper, a methodology for prediction of inprocess workpiece dynamics is presented, which is based on a structural dynamic modification using the FE model of the workpiece. The cutter location (CL) file is used to determine the removed elements at each tool location along a cycle. The proposed approach is demonstrated on example cases, and simulations are verified through experiments. (c) 2012 CIRP.