you say it cut fine on the xy axis,...well the plotter has only two axis x and y,...normally y is the axis that follows the blade carriage guide and x is the axis that follows the pinch rollers and material feed,...have you checked to see if the blade carriage has jumped off the extrusion,...or the belt driving the blade carriage has become loose or unfastened?,...do es the material feed freely or does it bind occaisionally,...any of these things can cause the symptoms you describe along with the problem Jim describes,...