Jyoti Hydraulic is a trusted name in the manufacturing of high-performance worm gear screw jacks designed for precision, stability, and safe industrial lifting. When designing any mechanical lifting system, one of the most important engineering tasks is calculating the correct load capacity your screw jack must handle. A wrong calculation can cause system failure, downtime, and even severe safety hazards.
This complete guide will help you understand how to calculate load capacity for worm gear screw jacks in a simple, systematic, and engineering-accurate way.

What Is Load Capacity in Worm Gear Screw Jacks?

Load capacity refers to the maximum load a screw jack can lift, support, or position safely without failure. It determines how much weight the jack can handle during lifting, lowering, or holding operations.

Load capacity generally includes:

Static load capacity
Dynamic load capacity
Side load or moment load
Buckling load limits
Duty cycle capability

Understanding load capacity is essential for choosing the right screw jack for your application.

Why Proper Load Calculation Is Important

Selecting a screw jack with incorrect capacity can lead to:

Overheating of worm gear system
Failure of the screw or nut
Excessive wear and shorter lifespan
Motor overload and breakdown
Operational failure during lifting
Safety hazards for operators

Correct load calculations ensure:

Safe lifting operations
Longer equipment lifespan
Smooth and reliable performance
Reduced maintenance cost
Compliance with industrial safety standards

Key Factors That Affect Load Capacity

Before calculating the load, you must understand the technical elements that influence screw jack capacity.

1. Type of Screw Used

The screw type directly affects load handling, speed, friction, and efficiency.

Trapezoidal Screw Jacks

Higher friction and lower efficiency
Very good load-holding capacity
No back-driving (self-locking)
Ideal for slow, heavy-duty lifting

Ball Screw Jacks

Low friction and high efficiency
Requires braking mechanism
Suitable for fast and frequent operations

2. Lifting Speed and Duty Cycle

High-duty-cycle applications generate more heat inside the worm gearbox and screw threads.
If your application requires frequent lifting, you must choose:

A screw jack with higher thermal capacity
Better bearings
High-quality lubrication

3. Buckling Load

This is one of the most critical factors.
If the screw extends too far, it can bend or buckle under load.

Buckling load depends on:

Length of screw extension
Screw diameter
End support conditions
Material strength

A longer stroke reduces load capacity, so this must always be calculated carefully.

4. Input Torque Requirements

Every screw jack needs a certain amount of torque to lift a given load.

Torque depends on:

Load
Pitch of screw
Gear ratio
Efficiency of the system

Higher loads require higher torque. You must check that your motor or manual input is capable of providing the required torque.

5. Safety Factor

Industrial lifting always requires a safety margin.
The safety factor compensates for:

Overload
Shock load
Imperfect alignment
Wear and tear over time

The recommended safety factor for screw jacks is between 2.0 and 3.0. For heavy-duty or critical applications, even higher factors may be used.

Step-by-Step Process to Calculate Load Capacity

Here is a simple and accurate method to calculate required load capacity for worm gear screw jacks.

Step 1: Calculate Total Working Load

Total load includes:

Weight of the object
Frictional forces
Acceleration forces
Any offset or side loads

Example:
If your machine requires lifting 5000 kg and frictional resistance is 10 percent,
Then:
Total Load = 5000 × 1.10
Total Load = 5500 kg

This is the base load before applying safety factor.

Step 2: Check Buckling Load

Buckling load must always be higher than the load you calculated above.
If the screw travels a long stroke, buckling capacity reduces.

Buckling load depends on:

Screw material
Screw diameter
Unsupported screw length
End mounting conditions

If buckling load is less than your required capacity, you must choose a screw jack with a bigger screw diameter or reduce the stroke.

Step 3: Calculate Required Torque

The screw jack must handle the required torque comfortably.
Torque calculation is based on:

Load
Screw pitch
Efficiency of screw jack
Gear ratio

If your motor does not supply adequate torque, the jack may not lift even if load capacity is sufficient.

Step 4: Check Gearbox and Mechanical Strength Limits

The worm gear and nut must withstand the pressure created by the load.
You must verify:

Gear strength
Bearing load limits
Bronze or alloy steel material limits
Thermal capacity under load

If the gear is overloaded, it will wear out quickly.

Step 5: Apply Safety Factor

This step is essential for industrial applications.
Assume your total load is 5500 kg.

With safety factor = 2.5:
Required Load Capacity = 5500 × 2.5
Required Load Capacity = 13750 kg

You must choose a screw jack with at least 14-ton capacity.

Understanding Different Types of Loads on Screw Jacks

To select a suitable jack, you must understand all the forces acting on the system.

1. Axial Load

The direct vertical load applied on the screw.
This is the main load the jack handles.

2. Radial Load or Side Load

Side loads should be avoided at all costs because screw jacks are not designed to take bending forces.
Even a small side load can reduce efficiency and cause thread wear.

3. Moment Load

Occurs when the load is not centered or evenly distributed.
This may require special mounting arrangements or multiple jacks working together.

4. Dynamic Load

Dynamic load appears during motion, especially acceleration and deceleration.
This type of load is higher than static load and must be included in calculations.

Example Calculation for a Multi-Jack System

Many industrial machines use multiple screw jacks connected with a single drive shaft.

Suppose:
Total load = 10000 kg
Number of jacks = 4

Load per jack = 10000 ÷ 4
Load per jack = 2500 kg

Add 10 percent friction:
2500 × 1.10 = 2750 kg

Apply safety factor of 2.5:
2750 × 2.5 = 6875 kg

Therefore, each jack must support at least 7 tons.

How Jyoti Hydraulic Ensures Accurate Load Capacity

Jyoti Hydraulic follows strict engineering standards to ensure the safety and efficiency of every screw jack.

Key advantages include:

Heavy-duty alloy steel screws
Precision worm gear and bronze nuts
High structural stability
Advanced design for long stroke applications
Customizable speed, stroke, and mounting design
CAD-based testing for buckling, torque, and thermal load
Compliance with industrial safety standards

Common Mistakes in Load Calculation and How to Avoid Them

These mistakes often lead to equipment failure:

Ignoring safety factor
Not considering screw buckling for long strokes
Using an undersized motor
Allowing radial or side loads
Miscalculating dynamic and shock loads
Using single jack for uneven load distribution

Avoiding these mistakes ensures smooth and reliable operation.

Conclusion

Calculating load capacity for worm gear screw jacks is essential for designing a safe and efficient lifting system. By correctly identifying the working load, torque requirement, buckling load, and safety factor, you can choose the right screw jack for your application.
Accurate calculations not only extend the life of the equipment but also improve operational safety and efficiency.

If you require professional consultation, load calculations, or customized screw jack solutions, expert support is always available.

Contact Jyoti Hydraulic

For technical guidance, custom design, or quotations, reach out anytime:

Phone: +91 9541424317
Email: info@jyotihydrauli.com

How to Calculate Load Capacity for Worm Gear Screw Jacks