A procedure with design and machining considerations is developed to define unsymmetrical turret motions of ribbed globoidal cams. Adjusting the parameters of rational B-splines to interpolate required angular motion constraints, one can refine the turret motion that is superior to those obtained by other traditional methods. To judge the geometric performance of the spatial cam surface corresponding to its turret motion, the envelope theory is applied to derive the analytical description of the cam surface. As a result, the pressure angle and the curvature of the cam surface can be investigated. A real example is illustrated to show the effectiveness of the procedure and the favorable results compared to those obtained by other means.