Diaphragm couplings are among the most precision-engineered flexible couplings available for high-performance motion control applications. With zero backlash, high torsional stiffness, and low inertia, they are the preferred choice for servo motors, stepper motors, and ball screw drives.

This guide explains the differences between single and double diaphragm couplings, helps you select the right configuration, and covers the key specifications you need to consider.

1. What Is a Diaphragm Coupling?

A diaphragm coupling is a metal flexible coupling that uses one or more stainless steel diaphragms to transmit torque while compensating for misalignment. It relies on the elastic deformation of the diaphragm to accommodate angular, radial (eccentricity), and axial deviations between connected shafts.

Key characteristics include:

• Zero backlash – No rotational clearance

• High torsional stiffness – Maintains system rigidity

• Low moment of inertia – Fast dynamic response

• Maintenance-free – No lubrication required

• High transmission efficiency – Up to 99.86%

2. Single Diaphragm vs Double Diaphragm – Key Differences

Why single diaphragm cannot compensate for eccentricity:
The single diaphragm coupling requires complex bending of the diaphragm. Due to structural limitations, it is not suitable for eccentricity (parallel misalignment).

Why double diaphragm can compensate for eccentricity:
The double diaphragm coupling has two diaphragm packs connected by an intermediate spacer. It can bend in different directions simultaneously to compensate for eccentricity.

3. Why Material Selection Matters

7075-T6 Aluminum Hubs

• Aircraft-grade aluminum alloy

• High strength-to-weight ratio – reduces inertia

• Excellent fatigue resistance – long service life

• Low moment of inertia – enables high-speed operation

304 Stainless Steel Diaphragm

• Corrosion-resistant – withstands harsh environments

• Oxidation-resistant – non-rusting

• High fatigue strength – millions of cycles without failure

• Acid and alkali resistant

4. Why Zero Backlash Matters for Servo & Stepper Motors

In precision motion control systems, backlash is the enemy:

• Servo motors – Backlash causes positioning errors and poor settling times

• Stepper motors – Backlash results in lost steps and inaccurate positioning

• Ball screw drives – Backlash creates lost motion and reduces accuracy

A zero backlash diaphragm coupling ensures that every motor rotation translates directly to load movement – no lost motion.

5. Key Specifications to Consider

When selecting a diaphragm coupling, evaluate these parameters:

6. Installation & Alignment Tips

Proper installation is critical for diaphragm coupling performance and longevity:

1. Clean shaft and bore – Remove oil, grease, and debris

2. Check alignment – Use a dial indicator to measure runout

   • For flanges <250mm, runout should not exceed 0.05mm

   • For flanges >250mm, runout should not exceed 0.08mm

3. Single diaphragm caution – Does not allow eccentricity – position carefully

4. Tighten screws evenly – Use a torque wrench in a star pattern

5. No lubrication required – Diaphragm coupling is maintenance-free

6. Set misalignment below 1/3 of allowable value – Extends service life

7. Applications Where Diaphragm Couplings Excel

8. Real‑World Example – CNC Machine Upgrade

A CNC machine manufacturer was experiencing positioning errors on a high-speed machining center. The existing coupling had measurable backlash, causing poor surface finish and scrapped parts.

They switched to Apex Coupling double diaphragm coupling (7075 aluminum hubs, 304 stainless steel diaphragm, zero backlash, H7 bore). Results:

• Positioning accuracy improved – backlash eliminated

• Surface finish enhanced – consistent machining quality

• Maintenance eliminated – no lubrication required

• Service life extended – 304 stainless steel diaphragm withstood millions of cycles

• Higher speeds achieved – low inertia enabled faster acceleration

9. Selection Checklist

• Configuration: Single (compact, high rigidity) or Double (eccentricity compensation)

• Material: 7075-T6 aluminum + 304 stainless steel diaphragm

• Backlash: Zero backlash for servo/stepper motors

• Bore tolerance: H7 for precision shaft fit

• Torque: 10000 N·m – select based on your requirement

• Speed: 9000 RPM – match your motor speed

• Screws: 12.9 grade for secure fastening

• Surface: Anodized for corrosion resistance

10. Conclusion

The single/double diaphragm coupling from Apex Coupling offers the perfect combination of zero backlash, high torsional stiffness, and low inertia for precision servo and stepper motor applications. With 7075-T6 aluminum hubs, 304 stainless steel diaphragms, H7 bore precision, and 12.9 grade screws, it delivers reliable, long-lasting performance in demanding industrial environments.

👉 Need a diaphragm coupling for your servo or stepper motor? Contact us with your configuration, torque, speed, and bore requirements.