Ball Screw Assembly Recirculation Systems

A ball screw assembly contains a number of parts, which includes the screw, ball screw nut and ball bearings. Other components are sometimes added, such as cages and wipers. Perhaps the most important part of the assembly is the recirculation system.

This is a critical piece of the entire ball screw assembly, as this is the mechanism that is used to ensure that each ball bearing moves from the bottom of the ball screw nut to the top. The recirculation system is solely responsible for maintaining a circuit of ball bearings, ensuring that the ball screw nut will move in a linear direction along the screw shaft.
 
There are quite a few designs for ball screw recirculation systems to choose from. Take as an example the end cap return ball nut, which makes use of a small cap added to the base of the ball screw nut. Another cap of the same size and design is also attached to the upper part of the ball screw nut. When a ball bearing reaches the bottom of the nut, the end cap collects it and it is redirected into a hole that has been pierced at an angle across the ball screw nut. It then falls into the other cap, which places it back into the raceway.

The external ball nut follows a similar idea, which recirculates the ball bearings using a separate tube. In order to redirect the balls into the tube a small pick up finger is included, and the ball bearings then roll along the tube back to the upper end of the ball screw nut, where they are then returned to the raceway.
 
Finally, another common design of recirculation system in ball screw assemblies is called the internal button ball nut. This type of recirculation system uses a machined button which includes a separate thread along which the ball bearings move to return to the top of the ball screw nut.