Tag Archives: design constraints for worm gear jacks

Worm Gear Essentials – Aesthetics

In the last of our series exploring the design considerations outlined in the white paper “How to Size a Worm Gear Screw Jack we look at the most esoteric of factors in determining the proper linear motion solution; the look of it.

Sometimes the “human element” determines some of the design considerations of a jack. For instance, a small jack could lift a ton, but because of its small appearance, people could perceive the jack to be unsafe. Therefore, in applications where the jack is visible, larger jacks are often specified to bring a sense of comfort and scale. However, when jacks are buried within an application or machine, these types of human interaction considerations are not necessary.

Other look and feel considerations should also be taken into consideration. Will the jack need to be assessable for regular maintenance? Will it be in near a heavily trafficked area, susceptible to accidental damage or contact? Will it be overhead, and more prone to the need to “look” safe? These may seem like fuzzy questions to ask, but they are just as important to consider as any factor with a seemingly simple equation.

Useful tools:

Design Guide Pro app

Definitions and technical data

Arrangement templates

Multiple jack arrangements

Worm Gear Essentials – Duty Cycle

How does the ratio of run time to total cycle time affect the design and layout of a worm gear jack system? Taken from the white paper “How to Size a Worm Gear Screw Jack,” this post looks at what a designer has to take into account to properly and safely answer that question.

Some of the mechanical energy input to a worm gear screw jack is converted into heat caused by friction. The duty cycle is limited by the ability of the worm gear screw jack to dissipate heat. An increase in temperature can affect the properties of some components resulting in accelerated wear, damage and possible unexpected failure.

Recommended duty cycles at max horsepower are:

  • Ball screw jacks = 35% (65% time off)
  • Machine screw jacks = 25% (75% time off)

The choice between a ball screw jack and a machine screw jack can dictate size. Ball screw jacks are often chosen for their efficiency, allowing for an increased duty cycle and a smaller size jack to move a given load.

Useful tools:

Jack application data form

Design Guide Pro App

Worm gear screw jack design considerations

Worm Gear Essentials – Column Strength

We’re looking at the elements that help a designer determine the right worm gear screw for an application, based off the excellent white paper “How to Size a Worm Gear Jack” from Ron Giovannone, Director of Application Engineering and Business Operations with Nook Industries in Cleveland, Ohio.

In this post, we look at how Column Strength factors into design considerations.

Column strength is the ability of the lift shaft to hold compressive loads without buckling. A compression load is a load that tends to squeeze the screw axially, which can cause buckling. With longer screw lengths, the column strength of the lift shaft may be substantially lower than nominal jack capacity.

In order to determine the compressibility of a given travel length, you must first determine your mounting condition.

A simplified formula to calculate the column strength in pounds is as follows:


Pcr          =             Maximum Load (lb)

d             =             Root Diameter of Screw (inch)

L              =             Distance between nut and load carrying bearing (inch)

Fc            =             End Fixity Factor

0.25 for mounting condition A

1.00 for mounting condition B

2.00 for mounting condition C

4.00 for mounting condition D

The above formula can only apply when the slenderness ratio (the length divided by the radius of gyration) is not exceeded.

Note: If you can ensure that the load will always be held in tension, you don’t need to consider column loading.

Related tools:

Inch Column Strength Calculator

Metric Column Strength Calculator

Worm Gear Essentials – Tonnage

This week, we continue our review of the white paper “How to Size a Worm Gear Screw Jack” by looking at the role Tonnage under load can affect the sizing of the linear motion system.

The load capacity of a jack is also limited by the physical constraints of its components, such as its drive sleeve, lift shaft or bearings. All anticipated loads should be within the rated capacity of the jack. Loads on the jack in most applications include: static loads, dynamic (or moving) loads, cutting forces or other reaction forces and acceleration/deceleration loads.

For shock loads, the peak load must not exceed the rated capacity of the jack, and an appropriate design factor should be applied that is commensurate with the severity of the shock.

For accidental overloads not anticipated in the design of the system, jacks produced by Nook Industries can sustain the following overload conditions without damage: 10 percent for dynamic loads, 30 percent for static loads.

Jack Application Data Form

Design Guide Pro App

Design Considerations

Download a Model

Engineering tools to make your work just a little easier.


white paper equations

Where can I go to help determine the proper size for my Modular Actuator application?  How much torque can my Ball Screw Assembly manage?  In theory, how long can I expect my Ball Nut to last?

Nook Industries provides a myriad of calculator options as a means of supporting the everyday needs of its customers.  Critical speed, column strength, unit conversion and more,  click here to view engineering support tools.


Can’t find what you need?  Call one of Nook Industries’ Application or Sales Engineers, who will discuss your requirements and offer the most suitable system to fulfill your requirements.

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