A Ball Screw is a threaded shaft that provides a spiral raceway for the ball bearings assembled in a nut. This combination provides a precision screw to enable controlled rotational motion to be converted into linear motion.
Ball Screws are able to withstand high thrust loads with minimal internal friction. They are made to close tolerances and are therefore suitable for use in applications where high precision is necessary.
While reducing friction, Ball Screws can operate with some preload, effectively eliminating backlash between input rotation and output linear motion. This feature is essential when they are used in computer-controlled motion-control systems e.g. CNC machines tools.
The four preload classes available in the standard nuts are P0 With Backlash, P1 No Backlash, P2 Light Preload and P3 Heavy Preload.
These low friction Ball Screws yield high mechanical efficiency compared to other alternatives. A typical Ball Screw may be 90% efficient, versus 50% efficiency for a trapezoidal thread of equal size. This low internal friction also means Ball Screws can be back driven (depending upon their lead angle) and therefore are usually unsuitable for hand operated machine tools, in which case trapezoidal thread spindle is the better choice.
Ball Screws are fabricated as either ground or rolled screw shafts. Although Ground Ball Screw is designed for the high precision requirements, Rolled Ball Screw, which is less precise and considerably less expensive, is still a mechanically efficient product to be considered.
Rolled Ball Screw can have positional precision as low as 0.003mm over 300mm of travel for high precision grade (C0) and 0.05mm for the same length of travel for a low grade (C7).
Whether using Ground or Rolled Ball Screw great care is needed to avoid contamination by dirt and other abrasive particles so as to maintain the inherent accuracy and ensure long life. This is easily and simply achieved by using rubber or leather bellows to completely or partially enclose the working surfaces.
Ball Screws are available from T.E.A. Transmissions .