Spring Preloaded Double Nut
Almost exclusively used with miniature ball screws, the spring preload maintains perfectly constant preload regardless of wear and manufacturing tolerances. Two nuts are installed in a housing. One is fixed, while the second one can slide longitudinally (a pin keeps it from rotating). A spring located in between the two nuts keeps the preload constant.
The advantages are obvious:
- Manufacturing tolerances will have no impact on preload and friction
- Preload can be very light and the ball nut will never have play regardless of wear etc.
There are also some disadvantages:
- The double nut with its housing is bulkier and more expensive
- The slip-fit of the second nut makes alignment more challenging
- The maximun thrust is limited by the spring - when exceeded, the spring will collapse causing play in the nut
The spring preloaded nut excels when it is not possible to keep manufacturing tolerances low enough to ensure very low and constant friction. This is the case when near zero friction is necessary while at the same time absolutely no play is acceptable, or if the screw is extremely long.
Please be aware that the spring preloaded nut has a maximum operating force equal to about 2/3 of the preload. We can increase preload to some degree upon request, but if peak loads exceeding the preload force cannot be avoided, then a single nut with rigid preload is preferred (miniature screw series 1112, 1214, 1412).