Inverted Rotating

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A machine screw mechanical actuator is the perfect solution for lifting a heavy load with minimal force. And C.H. Bull has the perfect mechanical actuator for your application—we offer dependable, high performance Duff Norton machine screw actuators. A Duff Norton inverted rotating machine screw mechanical actuator will provide the reliability and performance you need.

Request a quote on an inverted rotating machine screw actuator, or contact us for more info.

Duff Norton Inverted Rotating Machine Screw Actuators

Available in capacities from 500 lbs. up to 250 tons, Duff Norton inverted rotating machine screw actuators are highly customizable (see below). This makes it easy to create a device that is tailored to your exact load-lifting requirements.

Operated manually or via pneumatic, hydraulic, or electric gear motors, Duff Norton machine screw actuators can be used singly, in pairs, or in multi-actuator arrangements, depending on your application. Most models operate at a uniform speed, allowing actuators of varying capacities to be used on the same load simultaneously.

As most of these inverted rotating machine screw actuators are self-locking, they will hold heavy loads in place indefinitely. They can push, pull, apply pressure, or be used as linear actuators. They’re furnished with standard raises in increments of 1”, with total raises up to 20’ available. 

Various screw end options are available, including plain ends, threaded ends, clevis ends, and top plates. Optional limit switches can be installed to regulate the actuator’s vertical travel (up or down).


•    Positive, mechanical positioning
•    Uniform lifting speed
•    Optional anti-backlash
•    Precision positioning within thousandths of an inch
•    Customizable (see below)

We also offer upright rotating, upright translating, and inverted translating rotating machine screw actuators, as well as Duff Norton ball screw actuators.

Customizable to Meet Your Application Requirements

To accommodate your unique load-lifting requirements, C.H. Bull can provide a customized inverted rotating machine screw mechanical actuator. With a range of customizable features, it’s easy to develop a custom actuator that provide the ideal performance for your application. Customizable options include:

•    Lifting capacity
•    Screw end type
•    Motor type
•    Stroke length
•    Limit switch
•    and more

Request a quote on the inverted rotating machine screw mechanical actuator your application requires. Contact C.H. Bull for more information on these or any of our quality products.

Selecting the Right Mechanical Actuator for Your Needs

Step 1: Define your operating parameters, including total load, load per actuator (if multiple actuators are needed), desired lifting speed, total travel required, load type, and ambient working temperature.

Step 2: Determine which actuator type is best for your needs. There are a number of factors that must be considered when choosing between a machine screw actuator or a ball screw actuator. Machine screw actuators are inherently load-holding, and are generally better suited to high-vibration applications. Ball screw actuators are faster, more efficient, and require less motor horsepower to move an equivalent load.

Step 3: Calculate the minimum actuator performance. Start by selecting an actuator with capacity greater than the load it will lift, then use the formulae below to calculate your needs.

For loads greater than 25% of actuator capacity, the torque should be considered proportional to the load.
A) Actuator torque (in.-lbs.) = Actuator load (lbs.) x worm torque at full load
Actuator capacity (lbs.)

(For loads under 25% of actuator capacity, add “Worm torque at no load” to the torque calculation above to account for frictional losses.)

Calculate the input RPM (WARNING: Shaft input should never exceed 1,800 RPM.)
B) Input RPM = Desired lifting speed (in./min.) x turns of worm for 1” lift

Calculate actuator input HP.
C) Actuator input HP = Actuator torque (in.-lbs.) x RPM
Compare the required input HP with the actuator’s maximum HP. If the required HP exceeds the maximum, an actuator rated for higher HP is required.

If a gear reducer will be used, motor HP must be multiplied by the efficiency of the reducer to calculate reducer output/actuator input HP.

For arrangements of multiple actuators, where two or more mechanical actuators are shaft driven from a single motor or gear reducer, add the input HP requirements of all actuators. If using a mitre gear box, allow for 2% power loss for every 90° turn in the power path.

Step 4: Determine the best actuator configuration. Consider the capacity, speed, and duty cycle requirements of your application to find the right actuator for your needs.

Step 5: If lifting an unattached or unguided load the mechanical actuator must be configured to extend the lifting screw when the actuator is in action. To keep the translating screw from rotating, Duff Norton mechanical actuators include a keyed shell and screw (for machine screw actuators) or a square nut inside a square cover pipe for the end of the lifting screw (for ball screw actuators).

Step 6: Verify your actuator selection. Be sure to double-check your application’s travel and load requirements, along with the ratio, speed, and capacity of the chose actuator. Determine which end fitting (plain end, top plate, clevis end, or threaded end) is best for your application.

Safety Warnings

Actuator input RPM should never exceed 1,800 RPM.

Never exceed the actuator’s static or dynamic capacities.

Never exceed the actuator’s specified horsepower limits. If the max HP must be exceeded, reduce the lifting speed, choose a different actuator ratio, or consider an actuator that offers higher capacity or better efficiency.
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