“…In fact the machine architecture has still some geometrical defect (perpendicularity, parallelism, position…), the machine presents uncertainties in kinematic movements (gaps, deformations, yaw, pitch or roll deviations) and the part presents set-up deviations. For the normal accuracy class N (over a range of 5 classes), 22 errors on the machined work pieces caused by deviations of main geometrical accuracy parameters of machine tools have been identified (Reshetov and Portman 1988 Works has been done to develop models for machine tool error (Reshetov and Portman 1988, Moon and Kota 2002, Tutenea-Fatan and Feng 2004, Ahn and Cho 1999, Eman and Wu 1987, for our purpose a model of machine tool deviations by homogeneous transformation matrix is used, so the same mathematical tool is used for modelling perfect and real machine. In the cases of small deviations a linearised expression of the displacement can be used and a small displacement matrix (equation 3) which describes the small displacement screw is used.…”