Abstract: Constructive solid geometry is a technique of representing parts by adding and subtracting a set of primitive shapes. Automatic tool paths to machine a part with a rotating cutter are generated by taking the constructive solid geometric description of the part and replacing every primitive shape by an offset primitive, larger or smaller than the part by the cutter radius. A planar section slice of the offset part has the property that the center of the milling cutter will traverse this section curve and form the original part without gouging. To machine efficiently, a series of parallel slicing planes are taken from top to bottom through the offset part. For each section curve, numerical control machine code is generated to direct the cutter to follow that path, and the part is automatically machined. The method applies to both rough and finish cutting.