THE SCHRILLO COMPANY - Manufacturer of ball screws, acme screws, jackscrews, lead screws, & linear actuators

What is Whirling? 

The Whirling process capitalizes on the latest advancements in cutting tool materials to quickly produce threads and screws to tolerances previously requiring grinding. Difficult threading operations, such very long shafts or very wide profiles can be easily machined by whirling. The superior surface finishes and closer tolerances of screws machined by whirling are ideal for today's demanding clients. CNC control gives the possibility to machine threads of variable or unusual pitches, tapered or variable root diameters, single or multiple starts. Ball Screws, Acme Screws, Worm Shafts, Feedscrews for Injection Molding are all excellent examples of workpieces ideally suited to whirling. The machine shown is capable of machining screws up to 4.252 diameter by 80" long. Long screws are supported by high precision follower rests on each side of the cut and traverse with the tool slide over the entire length of the screw. This machine has been designed from the first thought for whirling and has the inherent rigidity for cutting deep, wide profiles in tough materials and the necessary accuracy for cutting precision, close tolerance screws. The main spindle is actually a ultra precision rotary "C" axis having high torque and a resolution of 0.001 degrees.

Hard Whirling
Perhaps the most exciting metalcutting breakthrough is the recent introduction of hard whirling. LEISTRITZ has developed a process for precision machining hardened steels. Using a CBN insert, steels as hard as 65 HRc can be machined. CBN or Cubic Boron Nitride is the hardest material known to man, next to diamond. CBN has uniformly high hardness and abrasion resistance in all directions. The superior edge retention and hardness of CBN permits more effective cutting with less tool wear, which helps maintain part geometry for greater precision. Combine this tool material with the gentle, tangential cutting action of whirling, and you get a revolutionary process for cutting precision threads in hard materials. Like all whirling operations, hard whirling is done dry, without coolant. The chips, glowing orange hot, carry away nearly all of the heat of the cutting, leaving the workpiece cool. This minimizes any thermal geometry variations. The surface finish and profile accuracy is amazingly precise. Producing Ball Screws with hard whirling can eliminate a number of previously mandatory steps in the processing. For example, a typical ball screw would be rough machined in the soft state, case hardened, straightened, and finish thread ground. Very often long screws, that do not necessarily require thread grinding are ground, only to remove distortions and lead variations created by heat treating. A hard whirled ball screw, for example, can be machined to finished dimensions and tolerances without further machining. On screws that demand thread grinding, the hard whirling process can still save on machining time and minimize work-in-progress. Finish thread grinding is one of the most time consuming operations on long screws. By machining the thread profile to nearly ground accuracy, hard whirling reduces the amount of material to be ground and thus reduces the grinding time. This process allows us to stock as a raw material case hardened bars, thus completely eliminating the need for heat treatment in the process. This can greatly reduce the total process and improve lead times to our customers. 
In summary, the advantages of whirling are dramatic for many applications being done by conventional means today. Whirling is a viable process for machining screws or worms, and should be considered by anyone machining these parts.