Ball-screw-and-ball-nut assemblies have been used for over sixty years in a wide variety of applications. For example, conventional automotive braking systems include those which use a ball-screw-and-ball-nut assembly, wherein the brake booster serves as a housing, wherein the ball-screw is turned by a gear driven by an electric brake caliper motor, wherein the ball-nut is connected to the brake pad, and wherein rotation of the ball-screw axially moves the ball-nut. In some known ball-nut assemblies, an exterior tube extending above the ball-nut serves as a crossover for the ball bearings, as is known to the artisan. However, such exterior tubes demand close part tolerances which are expensive and difficult to achieve. Also, such protruding exterior tubes are not suitable for certain applications such as being housed in a brake caliper housing. In other known ball-nut assemblies, a crossover member insert is inserted into a radial through slot of the ball-nut from inside or outside the ball-nut. In one variation, a plurality of circumferentially-offset inserts are used wherein each insert provides access to load the ball bearings for, and defines a crossover-member portion of, a closed loop groove. The crossover member inserts and the exterior crossover tubes permit the ball bearings to crossover the helical threads of the ball-screw to keep the ball bearings in the closed loop grooves as is known to the artisan. The constant-depth helical groove on the exterior of the ball-screw is made using thread-making methods such as grinding, rolling, or whirling (wherein for whirling, the tool-head cutting angle and the tool-head eccentricity are fixed as the whirling-type external-diameter cutting machine cuts the thread). When using a crossover member, the helical groove on the interior wall of the ball-nut (not counting the crossover groove of the separate crossover member insert) is rough cut with a lathe, is sometimes followed by heat treating, and then is smoothed and sized with an internal grinder as is known to those skilled in the art.
Still, scientists and engineers continue to seek improved methods for making a ball nut and improved methods for making a ball screw.