1. A machine tool for machining crankshafts, comprising: (a) a frame having a fixed longitudinal axis; (b) workpiece holding means mounted in said frame for rotation about said axis and adapted to support and to be non-rotatably connected to a crankshaft centered on said axis; (c) a tool carriage slidably mounted on said frame for a displacement which is transverse to said axis; (d) first drive means for imparting an angular rotation to said workpiece holding means about said axis, (e) second drive means for displacing said tool carriage in said transverse direction; (f) control means for controlling said first and second drive means such that said angular rotation and said transverse displacement are each performed in a predetermined nonlinear relationship in response to independent control signals applied via mutually non-interactive drive channels; said control means comprising: (i) a first controller operatively connected to said first drive means for imparting a desired angular rotation to said workpiece holding means in response to an independently controlled rotation signal; (ii) a second controller operatively connected to said second drive means for imparting a desired transverse displacement to said tool carriage in response to an independently controlled displacement signal; (iii) a drive control computer for processing workpiece and tool data and for computing from said data a plurality of points of inflection and characteristic values defining a series of linear approximations of said predetermined nonlinear relationship, and for providing said independently controlled rotation and displacement signals corresponding to said approximations.