Backlash is the amount of free axial movement by the nut when the screw is held stationary. The axial movement is possible because of clearance between the nut threads, the bearing balls, and the screw threads. 

The amount of thread clearance can be reduced in a nut by installing larger diameter bearing balls, using double-nut designs, and other techniques. PBC Linear miniature ball nuts, backlash is reduced by installing larger diameter bearing balls to reduce the clearance in the threads. 

Standard backlash is <= 0.050 mm or <= 0.002 inch. 

Reduced backlash is <= 0.013mm or <= 0.0005 inch.

What does it mean that an actuator will “back drive”?

An actuator back drives when the force applied to the carriage of an actuator overcomes the resistance of the drive train and causes the carriage to move. A common situation when this can occur is an actuator operating vertically with a weight load on the carriage. When power to the driving motor is removed, the weight on the carriage may overcome the resistance of the drive train, and the carriage may drop. In such situations, a designer may choose a low efficiency drive system that will not back drive or a brake may be installed in the drive train. The brake would be used to lock the system when power is removed from the actuator’s motor.

Can ball screws be installed and used as received?

If ball screws are ordered with a specific lubricant called out, then they often can be used as received from the manufacturer. However, most ball screws ship from the manufacturer with only a rust inhibitor applied. The rust inhibitor is not a sufficient lubricant. Ball screws received with a rust inhibitor applied should be cleaned with a solvent and then a proper lubricant should be applied.