Rigid couplings are essential components in precision motion control systems where zero backlash, high torsional rigidity, and maximum torque transmission are required. Unlike flexible couplings, rigid couplings do not accommodate misalignment – they create a solid, direct connection between two perfectly aligned shafts.

This guide explains how rigid couplings work, their key advantages, critical installation requirements, and how to select the right model for your application – using the DN/DNG series as a practical example.

1. What Is a Rigid Coupling?

A rigid coupling is a one-piece mechanical device that creates a solid, backlash-free connection between two shafts. Key characteristics include:

• Zero backlash – No rotational clearance

• Ultra-high torsional rigidity – No angular deflection under load

• No misalignment compensation – Shafts must be perfectly aligned

• High torque capacity – Handles demanding applications

• Low inertia – Lightweight design for high-speed operation

• Maintenance-free – No moving parts or wear items

💡 Rigid couplings are specifically designed for servo motor applications where ultra-high precision and zero backlash are critical.

2. Rigid Coupling vs Flexible Coupling – Which One Do You Need?

When to choose a rigid coupling:

• Shafts are perfectly aligned

• Zero backlash is critical for positioning accuracy

• Maximum torque transmission is required

• High torsional rigidity is needed for precise control

• Maintenance-free operation is desired

3. Key Features of DN/DNG Rigid Couplings

Zero Backlash
No rotational clearance – precise positioning for servo and stepper motors.

One-Piece Integrated Structure
Maximum rigidity – no moving parts, no wear, long service life.

High Torsional Rigidity
No angular deflection under load – maintains system accuracy.

Low Inertia
Lightweight design enables high-speed operation and quick starts/stops.

Set Screw Fastening
Simple and secure shaft fixation.

Material Options

• DN series: High-strength aluminum alloy with anodized finish

• DNG series: SUS304 stainless steel for enhanced corrosion resistance

4. Critical Installation Requirement – Perfect Alignment

⚠️ Rigid couplings do NOT accommodate any misalignment. The shafts must be perfectly aligned during installation.

💡 Installation tip: Use a dial indicator or laser alignment tool to ensure perfect shaft alignment before tightening the set screws. Improper alignment will cause premature bearing failure and shaft damage.

5. Why Rigid Couplings Are Ideal for Servo Motors

Rigid couplings are specifically designed for servo motor applications requiring ultra-high precision and zero backlash:

• Zero backlash – No rotational clearance – precise positioning

• High torsional rigidity – No angular deflection – accurate torque transmission

• Low inertia – Enables rapid acceleration and deceleration

• High accuracy – Perfect shaft alignment – precise motion control

• High durability – No wear parts – long service life

6. Applications Where Rigid Couplings Excel

7. Real‑World Example – Servo Motor Upgrade

A machine builder was experiencing positioning errors on a servo-driven indexing table due to backlash in their existing coupling. The coupling had measurable rotational clearance, causing inaccurate positioning.

They switched to Apex Coupling DN rigid set screw coupling (aluminum alloy, zero backlash, set screw design). Results:

• Positioning accuracy improved – backlash eliminated

• System rigidity increased – no angular deflection under load

• Maintenance eliminated – no wear parts

• Torque transmission improved – secure set screw connection

8. Installation & Maintenance Tips

1. Check shaft alignment – Use a dial indicator to ensure perfect alignment (0 radial, 0 angular, 0 axial)

2. Clean shafts and bore – Remove oil, grease, and debris before installation

3. Slide coupling onto shafts – Ensure both shafts are fully inserted into the bore

4. Tighten set screws evenly – Use a torque wrench to specification

5. Verify alignment – Re-check alignment after tightening

6. No lubrication required – Rigid coupling is maintenance-free

7. Inspect periodically – Check for any signs of loosening or wear

9. Selection Checklist

• □ 

  Type: Rigid set screw coupling – for perfectly aligned shafts

• □ 

  Material: Aluminum (DN) or Stainless Steel (DNG)

• □ 

  Fastening: Set screw – simple and secure

• □ 

  Backlash: Zero backlash – for servo/stepper motors

• □ 

  Bore: H7 tolerance – match your shaft diameters

• □ 

  Alignment: Must be perfect – 0 radial, 0 angular, 0 axial

• □ 

  Inertia: Low inertia – for high-speed applications

• □ 

  Maintenance: Maintenance-free – no lubrication

• □ 

  Application: Servo motors, stepper motors, CNC, 3D printers, robotics

10. Conclusion

The DN/DNG rigid set screw coupling from Apex Coupling offers the perfect combination of zero backlash, high torsional rigidity, and low inertia for precision motion control applications. With aluminum or stainless steel construction, one-piece integrated design, set screw fastening, and maintenance-free operation, it delivers reliable, long-lasting performance in demanding industrial environments – provided that shafts are perfectly aligned.

👉 Need a rigid coupling for your servo motor application? Contact us with your bore size, material preference, and application requirements.