Ball Return Systems
Track-to-track (internal return)
In this internal ball return system each deflector serves one turn, which is one circuit (or ball circle). The deflectors lift the balls out of the track and over the outer diameter of the shaft and guide them into the next available track. The internal ball return is particularly compact and yields small diameters of the nuts. It is the ball return of choice for very small ball sizes and small leads.
Through-the-nut return (external return)
Steinmeyer's "UltraSpeed" return is normally used for lead/diameter ratios greater than 0.5. It is normally used with dual start threads. Balls are lifted off the shaft using a deflector at one end of the nut and then guided through a bore (internal to the nut body) to the other end of the nut, where a similar piece guides the balls back onto the thread. One pair of deflectors serves one circuit (i.e. one of the threads) which includes several turns.
End cap return (external return)
End cap return works very much like the previously described through-the-nut return, with the exception that the ball deflector function is executed using a (plastic) cap at both ends of the ball nut. Each cap serves as the ball return and also includes wipers. End cap return is normallly used for very large lead/diameter ratios. This style ball nut is only available as a flange nut.
Multiliner (internal return)
This internal ball return uses multiliners to lift the balls out of the track and over the diameter of the shaft and guide them directly into the next (or previous) track. The internal ball return is very compact and yields the smallest nut diameters among all ball return systems. It is also the ball return of choice for very small ball sizes and small leads.
Z-Ball return (external return)
The Z-deflection works like the track to track return described above, except there are multiple turns for each deflector. The balls are tangentially lifted off from the thread, guided through the return part made of plastic and then introduced again to the thread. This type of deflection is used for heavy duty ball screws with large balls.
Ball nuts require a means to recirculate balls. Without it, the ball path would not be closed and balls would fall out at the rear end of the nut.
Design of the ball return is the determining factor for the maximum speed at which the ball nut can safely operate. This is normally expressed by the DN value. The better the ball return system deals with mass forces of the balls, the higher the DN value. Manufacturers typically quote DN values from 60,000 for basic tube returns to 160,000 and higher, e.g. the UltraSpeed return from Steinmeyer.