<p>Blades are the largest number of parts in aero engines and gas turbines. A blade is generally composed of a closed free-form surface. Helical finishing tool paths have less times of empty cutting tool paths. In five-axis machining, bullnose milling cutters have large cutting width and good wear resistance. In order to generate helical tool paths for blades and meet the step error requirement in the tool feed direction, the cutting model of a bullnose milling cutter at a cutter contact (CC) point is established to analyze the geometric characteristics of the step error. The cutting process between adjacent CC points is discrete into multiple continuous tool locations. Similarly, the cutting edge of the bullnose milling cutter is discretized into multiple cutting circles, and the step error at a tool location is calculated iteratively. Then the step errors of discrete tool locations are calculated, and the maximum value is taken as the step error of the tool path between adjacent CC points. The first and last lines of tool paths and the tool paths in leading and trailing edges are generated by the row cutting method. In order to obtain smooth and reasonable helical CC curves on suction and pressure surfaces, a method is proposed by intersecting planes and the blade in three-dimensional space. Discrete CC points are obtained on helical CC curves and helical tool paths are calculated. The step errors of all tool path are calculated. New CC points are added to generate new tool paths for the step error requirement and redundant tool paths are deleted. Finally, the feasibility and effectiveness of the proposed method are verified by an example.</p>