Advances in Ball Screw Machining - World Class Ballscrew Manufacturers Discover Huge Advantages In Whirling.

Allendale, NJ -- Producing both aerospace flight control actuators and commercial ballscrew assemblies for linear motion control, companies like Thomson Industries and Umbra Cuccinetti have eliminated several processing operations by whirling ball threads in hardened materials without previous roughing. Whirling using CBN cutting inserts with either a full round or gothic arch profile has allowed them to produce finish quality screws in a single pass.

Leistritz, a machine tool builder in Nuernberg, Germany with offices in Allendale N.J., has developed a unique process solution by combining precision follower rests, an economical resharpenable tool system, and a high-speed whirling head in a rigid and accurate CNC controlled machine tool. With bed lengths up to 8m long, ball screws can be whirled to finish tolerances in a single pass in full material. By clamping the finished outer diameter in carbide "V" jaws, the follower rests on either side of the cut to guarantee near zero concentricity of the thread.

Whirling is a dry-cutting process and coolant is not used. This saves the expense of maintaining a coolant system and disposing of toxic grinding swarf. The tangential cutting action of the whirling process combined with optimum speeds and feeds permit machining of steels as hard as 65hrC with minimal heat transferred to the workpiece. After whirling the material is only slightly warm to the touch, with an increase of approx. 20-25°F above ambient. Since whirling is performed by cutting from the tailstock toward the chuck, any slight lead variation caused by this temperature increase is "behind" the cut, and does not effecting the cool/stable bar yet to be whirled. Lead accuracies of ±0.0005"/foot are easily attained when cutting stable materials. Leistritz machines are laser calibrated at the factory and installation site to insure positioning accuracy.

Ball forms of 0.062" ball to 0.500" have been efficiently whirled in this manner with huge time savings compared to grinding. Leistritz whirling machines can offer 8 to 10 times savings over thread grinding with no fear of surface cracking. Since whirling uses ideal cutting geometry, the material never reaches a critical temperature and stress does not enter the work. Screws that are whirled have surface finishes to Ra 8 microinches, and are not visibly different from ground screws.

Provided by: Thomson Industries Inc.