The geometric characteristics of the machined sur� face of a blank (slab) are mainly determined by the motion of the cutting system's components, which depend on the external dynamic forces due to the machining process. A key factor here is the highspeed spindle of the metalcutting machine, on which the tool is mounted. The spatial motion of the spindle's axis will depend on the structural imbalances of the mill, noncoaxiality of the mill and spindle after attach� ment, imbalances of the spindle, and changes in the cutting force due to the unstable properties and vari� able margin of the blank. The spindle is mounted in bearings 1 and 2 (Fig. 1a) and supports a complex mill 3 (by cantilever attachment). Longitudinal slots in mill 3 accommo� date cutting plates 4, made of tool material. Cutting plates 4 remove surface layer 7 and knots 5 randomly distributed in the material (Fig. 1b). The machined material of slab 6 is nonuniform, with variation in the hardness, the density, and the margin. The external working load on the cutting system consists of the cutting force, the unbalanced centrifu� gal force due to primary imbalance vector Dst of the spindle, and the bending torque M of the pair of iner� tial unbalanced centrifugal forces P1-P1 due to the presence of primary imbalance torque MD in the spin� dle. The increments in the cuttingforce components P z and P y are due to machining of the knots within the slab. In addition to these increments, an axial compo� nent P i appears in machining the knots. By x 1 , y 1 , x 2 , y2, respectively, we denote small displacements in the first and second bearings in the direction of the X and Y axes, with vibration of the mill's spindle in machining.