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

The post Worm Gear Essentials – Aesthetics appeared first on Making Motion Work.

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

The post Worm Gear Essentials – Duty Cycle appeared first on Making Motion Work.

One of the benefits of using ball screw-style jacks is the ability to predict the theoretical life of the ball screw. The life of a ball nut used in a ball screw-style jacks can be easily calculated by using the following formula:

WHERE:

T_x  =  Travel other than rated load

F_r   =  Rated Dynamic Load for the ball nut

F_x  =  Actual or Equivalent load

T_r   = Rated Travel Life. For inch screws this is equal to 1,000,000 inches

For manufacturers wishing to extend the life of their screws, it can be beneficial to order a larger size jack than normally required, extending the life of the screw.

Since jack products often work in environments full of dirt and debris, manufacturers take multiple precautions to keep out contamination and preserve the life of the screw. Some manufacturers utilize bellows boots that expand and contract as the nut moves along to keep the lift shaft covered from contamination. Bellows boots can be supplied in numerous materials so that they may be applied in even the most extreme applications.

With ball screw jacks, another form of protection manufacturers use is wipers. Nut wipers can be felt or plastic, and brush the nut free of any dirt or other contaminants, keeping contaminants from entering the ball nut.

Related tools:

Bellows Boots Design

Boot Data Form

Design Guide Pro App

The post Worm Gear Essentials – Life appeared first on Making Motion Work.

Critical speed is the speed that excites the natural resonance frequency of the screw. The critical speed will vary with the diameter, unsupported length, end fixity and rpm of the screw. Since critical speed can also be affected by the shaft straightness and assembly alignment, it is recommended that the maximum speed be limited to 80 percent of the calculated critical speed. Due to the slow speeds at which jacks move, it is often not a large concern when choosing the size of a jack. However, critical speed should still be measured when making design considerations, especially when considering longer travel lift shafts.

Here is a simplified formula used for calculating critical speed for jacks:

WHERE:

N       =                Critical Speed (rpm)

d       =                Root Diameter of Screw (inch)

L        =                Length Between Bearing Supports (inch)

C_s      = End Fixity Factor

0.36 for mounting condition A

1.00 for mounting condition B

1.47 for mounting condition C

2.23 for mounting condition D

Related Tools:

Acme critical speed chart

Ball critical speed chart

Inch critical speed calculator

Metric critical speed calculator

The post Worm Gear Essentials – Critical Speed appeared first on Making Motion Work.

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:

WHERE:

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

The post Worm Gear Essentials – Column Strength appeared first on Making Motion Work.

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

The post Worm Gear Essentials – Tonnage appeared first on Making Motion Work.

This week, how Horsepower limitations can affect jack sizing.

When determining the lifting power of a jack, it’s a common mistake to assume the lifting capabilities of a jack are determined solely by its tonnage size. The load’s capacity is more often determined by its horsepower limitations. For example, a 10-ton jack may only be able to lift a one-ton load, because it is temperature-limited by the working horsepower it requires to lift the load.

The horsepower limit of the jack is a result of its ability to dissipate the heat generated from the inefficiencies of its components. The maximum horsepower value represents the point at which the heat that is generated by the working horsepower to move a given load meets the maximum temperature of the internal components. The working horsepower to move a given load is calculated by using the following formula:

How well a jack can dissipate heat is influenced by many application-specific variables, including mounting, environment, duty cycle and lubrication. The best way to determine whether performance is within horsepower limits is to measure the jack temperature. The temperature of the housing near the worm gear must not exceed 200 degrees Fahrenheit.

Looking for help in figuring out the right horsepower? Here are some tools:

Calculate Horsepower with this calculator

Calculate Kilowatts

Worm gear jacks definitions and technical data

The post Worm Gear Essentials – Horsepower appeared first on Making Motion Work.

4 Mistakes to Avoid Designing an Electromechanical System

The post Electromechanical Systems appeared first on Making Motion Work.

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“Do we have the structure and resources (staff and inventory) to support end users if troubleshooting and repairs are needed?
How easy is it for the user to perform basic maintenance?”  

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The post Linear Actuators appeared first on Making Motion Work.