How A Ball Screw Works
 

A. The Ball Screw Assembly
The ball screw assembly consists of a screw and a nut, each with matching helical grooves, and balls which roll between these grooves between the nut and the screw when the nut or screw is rotating. The balls are deflected by the deflector into the ball return system of the nut and they travel through the return system to the opposite end of the ball nut in a continuous path, and exit from the ball return system into the ball screw and nut thread raceways continuously to recirculate in a closed circuit.

B. The Ball Nut Assembly
The ball nut determines the load and life of the ball screw assembly. The ratio of the number of threads in the ball nut circuit to the number of threads on the ball screw determines how much sooner the ball nut will reach fatigue failure (wear out) than the ball screw will.

C. Ball Nuts Are Manufactured With Two Types of Return Systems

(a)The External Ball Return System
In this type of return system, the ball is returned to the opposite end of the nut through a ball return tube which protrudes above the outside diameter of the ball nut.

 

 

 

(b) The Internal Ball Return System (There are several variations of this type of return system) Example (1)

The ball is returned through or along the nut wall, but below the outside diameter. Some manufacturers have one revolution circuits where the balls are forced to climb over the crest of the thread by the return system. This is known as a "flop-over."

The Internal Ball Return System of the flop-over design originated in England and is used extensively in Europe. In the 1950's Rotex of England licensed Scully Jones in the United States to build the flop-over design. This venture failed in the early 1970's. This design has been copied by Japan, China, India, Spain, West Germany, Belgium, France and many other countries including the U.S.A. In the internal deflector type of ball screws, the balls make only one revolution of the shaft and the circuit is closed by a ball deflector (B) in the nut (C) allowing the ball to cross over between adjacent grooves at points (A) and (D).

 

 

(c) The Internal Ball Return System
Example (2)
In this type of return system, the ball is returned to the opposite end of the nut through or along the nut wall, but below the outside diameter through a hole.
 

(d) The Internal Ball Return System used by Barnes Industries
In this type of return system, the ball is returned to the opposite end of the nut through or along the nut wall, but below the outside diameter through a "V" cap.
 

* 17-4 PH Stainless steel was chosen for its toughness and work hardening characteristics which give the components exceptional wearability.