Deviations of sizes and spatial form of workpieces from nominal values can have significant effect on the results of machining. To study this influence, we carried out the analysis of deviations of a plate form from V95pcht2 alloy with the size of 3500х1600х35 mm [19]. After removing a 4 mm allowance from this plate, the plate was separated from a vacuum table caused by the cumulative influence of tension from fixing and imbalance of thermal residual stress diagram. According to preliminary measurements of deviations from flatness the plate conformed to technical requirements of GOST 17232-79 – deviations on a 1000 mm base did not exceed 3 mm at admissible 5 mm. However, the measurements of deviations from surface flatness of a plate on a 200 mm base showed that they have complex fluctuating nature (Figure 2)