What’s the anti-backlash device?

anti-backlash screw jack

Anti-backlash devices are internal jack components used to minimize backlash (free movement between the lifting screw and nut) in machine screw jacks. You can use it to reducer machine screw backlash.  Please note for ball screw jack and bevel ball actuators, the use of oversized ball bearings in ball nut assemblies is recommended to reduce endplay.

Why use anti-backlash screw jack?

Even the best manufacturing processes produce clearances between a screw and a mating nut. In applications where loads maybe in either direction, backlash
can result from these clearances creating unacceptable movement in the controlled mechanism as loads change. These applications are common in the paper, plastic, film, sheet metal forming processes, satellite, or other load-reversing applications.

Such as steel mill applications where the screw jacks are used to set and maintain the position of the movable upper roll of a rolling mill. In operation, the initial weight of the roll pulls the lifting screw to one side of the nut. When steel passes through the rolls, the load reverses on the lifting screw and movement in the opposite direction is limited by the anti-backlash device.

These applications may be subjected to extreme vibrations. These vibrations can produce constant movement between the screw and lifting nut which can hammer the threads and cause premature wear. To reduce this screw-to-nut backlash to an absolute minimum, that’s where Anti-Backlash jacks are used.

Can anti-backlash device be adjusted?

When the internal nut threads begin to wear, lifting screw backlash increases. The anti-backlash device allows the backlash to be adjusted to a minimum value practical. As wear occurs, the jack can be easily adjusted, without any disassembly, to return the backlash to its’ original minimum value.

Adjustment frequency will vary depending on load, duty cycle, and temperature. To avoid binding and excessive wear, do not adjust lifting screw backlash to less than .0005”. The anti-backlash device should be replaced when no further adjustment is possible due to tread wear.