What Is the Difference Between Rigid and Flexible Couplings?

Choosing the right coupling keeps your machinery running efficiently. If the wrong coupling is used, even minor misalignments or vibrations can become major problems, such as accelerated wear, strain on bearings, and potentially extensive shutdowns causing unexpected downtime.

There are two main types of coupling: rigid and flexible. Each type serves a distinct purpose and performs best under specific operating conditions. Understanding the difference between rigid and flexible coupling ensures you make informed decisions that optimize your system’s performance.

What Is a Rigid Coupling?

Rigid couplings are the simplest type of couplings connecting two shafts. The shafts must be perfectly aligned, since rigid couplings do not allow any misalignment. This is very difficult to achieve and is seldom attained. Even with a good initial alignment, changes can occur over time, such as foundation settling or thermal growth. A rigid coupling would not compensate for these changes and could lead to premature wear of drive train components.  Rigid couplings are commonly used in applications where a precise rigid connection is required, such as machine tools or robotic assemblies. Because they eliminate movement between shafts, rigid couplings deliver consistent torque transfer while maintaining a precise alignment.

Design and Function

These couplings are typically made from steel, stainless steel, or aluminum, and use bored holes, keyways, or set screws to secure the shafts to the hubs. Some designs feature flanges or split clamps for easier installation and maintenance.

In operation, a rigid coupling transfers torque directly from one shaft to the other with no flexibility or damping. Because of this design, they deliver precise power transmission and perfect alignment.

However, these coupling types cannot absorb vibration or handle misalignment. Because of this, rigid couplings are best suited for fixed, high-precision systems.

Common Types of Rigid Couplings

• Sleeve Coupling: This type is outfitted with a solid cylindrical sleeve to connect two keyed shafts, resulting in a solid joint for torque transmission.
• Flanged Coupling: A flanged coupling features two flanged rigid ends that are bolted together.
• Clamp Coupling: The clamp coupling consists of two split halves that tightly secure around the shafts.

Advantages

• Consistent Torque Transmission: Rigid couplings deliver torque transfer with minimal power loss, maintaining consistent performance between connected shafts.
• Simple, Low-Cost Design: This type of coupling features a straightforward design and is the lowest cost type of power transmission coupling. 
• Ease of Installation: Because of their straightforward design, rigid couplings take little time to install. 
• Precision Alignment: Rigid couplings keep both shafts perfectly centered, creating a solid connection. 

Disadvantages

• No Misalignment Compensation: Rigid couplings do not accommodate misalignment. Compensating for minor misalignment between two shafts is a requirement for most industrial applications to protect the drive train components.

• No Vibration Dampening: Vibration naturally occurs in a system, and a rigid coupling will not dampen any of the vibration. This could lead to wear and premature failure.
• Precise Alignment: Precise alignment is needed for a rigid coupling, and this may often mean significant resources and time to achieve is required and is not always practical.

What Is a Flexible Coupling?

A flexible coupling connects two shafts while allowing a small amount of movement or misalignment between them, and it is designed to handle the real-world imperfections that come with rotating machinery. Two perfectly aligned shafts is not practical in industrial applications. 

Design and Function

A flexible coupling connect two shafts but leaves room for a little movement between them. There are different types of flexible couplings. Different types of flexible couplings exist and can use components such as elastomeric inserts, metal discs, or spring grids that can flex when the system runs. Flexible couplings absorb vibration, soften torque spikes changes, accommodate misalignment and protect the rest of the components of the drive train.  This results in increased reliability and longer equipment life.

Common Types of Flexible Couplings

• Jaw Coupling: A jaw coupling connects two hubs with an elastomer insert that flexes as the shafts turn. It helps reduce vibration and noise while protecting other components from sudden torque spikes.
• Gear Coupling: This design uses lubricated geared teeth that mesh inside a sleeve, allowing misalignment. 
• Grid Coupling: A grid coupling relies on a flexible steel spring that fits into grooves on both hubs. The spring bends slightly under load, helping to absorb shock loads. 
• Disc Coupling: Thin metal discs form the flexible element in this design. They flex just enough to offer minimal misalignment between shafts. 
• Elastomeric Coupling: Made with elastomeric inserts, this type of flexible element dampens vibration-dampens, handles misalignment, and is suitable for a wide range of industrial applications. 

Advantages

• Vibration Dampening: Flexible couplings help smooth out system operation by absorbing vibration and reducing noise, which keeps machinery running more efficiently.
• Protection from Shock Loads: They can cushion sudden torque spikes and prevent damage to connected components.
• Reduced Wear: By easing strain on bearings and seals, flexible couplings help prevent premature wear and extend equipment life.
• Handles Misalignment: They can adjust for small angular or parallel misalignments between shafts, maintaining steady torque transfer even when conditions change over time.
• Limitations: Flexible couplings can cost more upfront and depending on the coupling type may require extensive maintenance. Despite this, due to their protective benefits, using them results in a lower total maintenance cost for your machinery in the long run.

Rigid vs. Flexible Coupling — Key Differences

If you’re comparing rigid coupling vs. flexible coupling, it helps to focus on how each performs under different conditions. The table below summarizes the key differences:

When To Use Rigid vs. Flexible Couplings

Choosing between these two coupling types depends on how your system operates. We recommend using a rigid coupling for high-precision setups. In contrast, you should use flexible couplings for systems where there is misalignment, vibrations, and in systems where a protective function is needed to protect more expensive components of the drive train. 

U.S. Tsubaki’s Atra-Flex® Couplings are trusted in industrial applications worldwide. Atra-Flex couplings offer misalignment capabilities, vibration dampening without needing lubrication or extensive maintenance. Our replace-in-place design means inserts can be changed out in minutes without moving hubs or connected equipment. Our product line includes the T-Series and the M-Series — each model is engineered to handle specific torque, load, and alignment requirements.

For enhanced durability, consider Atra-Flex® OnyxShield protection for wet or corrosive environments for the longest life out of your flexible coupling. 

FAQs

What is the main difference between rigid and flexible couplings?

The difference lies in flexibility. Rigid couplings demand perfect alignment, while flexible couplings absorb vibration and accommodate minor misalignments.

Can flexible couplings handle more torque?

Typically, rigid couplings transmit more torque due to their solid structure. However, high-quality flexible couplings like U.S. Tsubaki’s Atra-Flex® models can handle significant torque while reducing stress on the connected equipment.

Which coupling is best for misalignment?

Flexible couplings are best for misalignment. Their elastomeric or metallic components flex slightly to compensate for angular or parallel shaft offset.

Do flexible couplings require more maintenance?

Flexible couplings may require periodic inspection depending on the type, but can contribute to less overall wear of your system. Atra-Flex couplings are a minimal maintenance solution requiring no lubrication and can simplify your maintenance activities. 

Find the Right Coupling for Your System

Both rigid couplings and flexible couplings serve valuable purposes, depending on your system’s needs. The key is to match the coupling to your machine’s requirements.

At U.S. Tsubaki, we offer a complete line of Atra-Flex® Couplings built for strength, reliability, and long-term performance. Explore our full catalog or request a quote to get started. You can also connect with our team online for expert guidance on your specific application.