BALLSCREW ASY;20Z VMC15-4020 INCH

This is the complete assembly, ball screw and bearing mount.

Why Buy a New Ball Screw?

We offer new replacement ball screws for your Fadal machine, but many customers ask us about the quality differences between a rebuilt ball screw and a new ball screw. Over the years, we have worked with different manufactures and rebuilders, and rebuilding a ball screw is rarely as simple as it may seem. An honest rebuilder should tell you up front that a rebuilt ball screw and nut will often not perform as well as a new screw, and most likely will not last as long.

Why? Here are three important aspects that must be addressed.

1. The screw itself can easily be damaged beyond repair. When the recirculating balls decay, they start to “skid” as they become breakdown and loose roundness. Often, by the time you hear the problem, the damage has already occurred. The skidding of the ball causes a galling effect on the ground surface of the screw. This damage is not easily repaired, and even a manufacture has a difficulty doing a regrind of the initial track. Even with only minor damage, as the screw gets smaller from the regrind, the replacement balls must get larger to mate with the Ball Nut side of the contact. Remanufacturers only have a certain selection of varying ball sizes so a successful regrind is rare. The second option is to polish the screw and try to remove any skid marks on the screw. While the results might look good to the “naked eye”, this often creates an audible sound.
2. As the screw is used over time, they can get worn areas that develop, making it difficult to size the replacement balls so that they are not loose in one area and tight in another. In this case, the rebuilder can only use a smaller ball with much less preload.
3. When the screw has “skid” damage, the Ball Nut will also have the same problems as described above. Typically, the nut must be replaced, because it is difficult to remove the damaged surfaces.

The bottom line is that the final difference cost between a new ball screw and a repaired one is only a couple of hundred dollars, but the performance is usually noticeable, depending when the old screw was stopped being used. The savings is not worth installing a screw that underperforms a new replacement. 

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 providing the only contact between the nut and the screw. As the screw rotates, the balls are deflected into the ball return system of the nut and they travel through the return system to the opposite end of the ball nut to create a continuous path. The balls then exit from the ball return system into the ball screw and nut thread raceways to create a closed circuit.