Anti-Backlash Option

How Anti-Backlash Feature Works
When the screw (1) is under a compression load, the bottom of its thread surfaces are supported by the top thread surfaces of the worm gear (2) at point (A). The antibacklash nut (3), being pinned to the worm gear and floating on these pins and being adjusted downward by the shell cap, forces its bottom thread surfaces against the upper thread surfaces of the lifting screw at point (B). Thus, backlash between the worm gear threads and the lifting screw threads is reduced to a regulated minimum. When wear occurs in the worm gear threads and on the load carrying surfaces of the lifting screw thread, the load carrying thickness of the worm gear thread will be reduced. This wear will create a gap at point (B) and provide backlash equal to the wear on the threads. Under a compression load, the lifting screw will no longer be in contact with the lower thread surface of the anti-backlash nut. Under this condition, backlash will be present when a tension load is applied. The anti-backlash feature can be maintained simply by adjusting the shell cap until the desired amount of backlash is achieved. To avoid binding and excessive wear, do not adjust lifting screw backlash to less than .0005". This will reduce the calculated separation (C) between the anti-backlash nut and the worm gear and will reduce the backlash between the worm gear threads and the lifting screw to the desired minimum value. When separation (C) has been reduced to zero, wear has taken place. Replace the worn gear and backlash nut set at this point. This feature acts as a built in safety device.

Note: Use anti-backlash as a safety device or to provide wear indication for critical applications. Keyed anti-backlash models may require key adaptor, which projects below jack base. Consult Duff- Norton for dimensions.

4800 & 9400 Series with Anti-Backlash Feature
For applications where a reversal of loading from tension to compression is encountered, 1800 and 9000 Series actuator models in a wide range of capacities are available equipped with anti-backlash nuts. These are designated as 4800 and 9400 Series. The anti-backlash nuts reduce the vertical backlash between the screw and the worm gear nut to a practical minimum for smoother, more precise operation and minimum wear. They also act as a safety device, providing a dual-nut load carrying unit, when worm gear becomes worn. Torques, actuator efficiency ratings, weights and in some instances closed heights of 4800 and 9400 Series differ from those of 1800 and 9000 Series. See table below. All actuator units can be supplied with standard raises up to 24 inches. Consult factory for special raises up to 20 ft. For compression loads refer to page 112.

Configuration Option

Upright Translating	Double Clevis	Upright Rotating
Inverted Translating		Inverted Rotating

Screw End Option

Top Plate

Threaded End

Clevis End

Screw Keying

For proper function, the lifting screw of translating screw actuators must be restrained to prevent rotation. It is preferable that the restraint be provided by the application, but, when necessary, translating machine screw actuators can be internally keyed to prevent lifting screw rotation.

Important points that should be considered before internal keying is specified,

• Actuator life can be significantly reduced.
• Actuator cost is increased.
• Standard keyed inverted actuators do not typically include a cover pipe. A cover pipe can be provided at additional cost - Consult Duff-Norton Application Engineering.
• For actuators without anti-backlash, keying is accomplished by a keyway along the length of the lifting screw sliding over a stationary key in the shell cap. For actuators with anti-backlash, keying requires the addition of a key adaptor at the base of the shell

Closed Height

Upright Configurations
Upright Top Plate	Upright Clevis End	Upright Threaded End
Inverted Configurations
Inverted Top Plate	Inverted Clevis End	Inverted Threaded End

Left Hand Worm Extension

Standard Double Extension	Left Hand Worm Extension	None
Close Mount Limit Switch	Encoder	C-Face Adaptor
Extended Mount Limit Switch		Reducer

Right Hand Worm Extension

Standard Double Extension	Right Hand Worm Extension	None
Close Mount Limit Switch	Encoder	C-Face Adaptor
Extended Mount Limit Switch		Reducer

Left Hand Limit Switch Mounting Position

Close Mount Limit Switch
Position 1	Position 2	Position 3	Position 4
Extended Mount Limit Switch
Position 1	Position 2	Position 3	Position 4

Right Hand Limit Switch Mounting Position

Close Mount Limit Switch
Position 1	Position 2	Position 3	Position 4
Extended Mount Limit Switch
Position 1	Position 2	Position 3	Position 4

Left Hand Reducer Mounting Position

Position 1

Position 2

Position 3

Position 4

Right Hand Reducer Mounting Position

Position 1

Position 2

Position 3

Position 4