Telescopic universal joints (also known as extendable cardan shafts) are essential for transmitting power between shafts with both angular misalignment and variable axial spacing. The WSP series from Apex Coupling offers a versatile solution with sliding or needle bearing options, covering torque ranges from 25 to 6300 N·m with speeds up to 4000 RPM.

This guide explains how telescopic universal joints work, the differences between bearing types, and how to select the right model for your application.

1. What Is a Telescopic Universal Joint?

A telescopic universal joint consists of:

• Two yokes (forks) – precision-machined from 40Cr alloy steel

• A cross shaft – the central torque-transmitting component

• A telescopic spline shaft – allows axial length adjustment

The telescopic design makes repositioning simpler and faster than double universal joints. In cases of axial misalignment, the length can be easily adjusted without disassembling the shaft assembly, significantly reducing maintenance downtime and improving operational efficiency.

💡 Telescopic universal joints are widely used in packaging machinery, woodworking equipment, multi-spindle drills, and general automation where shaft spacing varies during operation.

2. Sliding Bearing vs Needle Bearing – Which One Do You Need?

Recommendation:

• Choose sliding bearing for heavy-duty, low-speed applications with shock loads.

• Choose needle bearing for high-speed applications (above 1000 RPM) where precision and low friction are priorities.

⚠️ Note: It is recommended to use the coupling at ≤50% of the maximum rated speed for optimal service life.

3. Operating Angle – 30° Working vs 45° Limit

The WSP series is designed for smooth operation up to 30° in continuous use. The absolute limit per joint is 45°.

Practical tip: For most applications, try to keep operating angles below 30° for continuous operation to maximize service life.

4. Telescopic Travel – Variable Shaft Spacing

The WSP series features telescopic travel that allows the coupling to accommodate:

• Thermal expansion – changes in shaft spacing due to temperature

• Installation tolerances – minor misalignment during assembly

• Variable positioning – applications where shaft spacing changes during operation

Length Calculation Formula:

• Stroke: Xs = (Lmax – 2·L2 – B) / 2

• Minimum length: Lmin = L2 + B + X + L2

💡 Custom telescopic travels are available on request for specific application requirements.

5. Material & Hardness – Why 40Cr + Hardened Components?

The WSP series is manufactured from 40Cr alloy steel with hardened components:

✅ This combination ensures high strength, excellent wear resistance, and long service life in demanding applications.

6. Applications Where Telescopic Universal Joints Excel

7. Real‑World Example – Packaging Line Upgrade

A packaging machinery manufacturer was experiencing premature wear on standard universal joints used in their conveyor drives. The joints operated at 25° angles and 1800 RPM, causing frequent failures and downtime.

They switched to Apex Coupling WSP needle bearing telescopic universal joints (40Cr, needle bearing, 4000 RPM, H7 bore). Results:

• Service life extended – needle bearing handled 1800 RPM smoothly

• Telescopic adjustment – accommodated variable shaft spacing

• Angle capacity – 25° well within the 30° recommended range

• Vibration reduced – H7 bore improved concentricity

• Less downtime – fewer replacements during production

8. Installation & Maintenance Tips

1. Check alignment – Keep operating angles ≤30° for continuous operation

2. Lubricate sliding bearings – Regular lubrication extends service life

3. Needle bearings – Sealed, low maintenance – inspect periodically

4. Check for wear – Inspect cross shaft, center slider, and pins periodically

5. Dynamic balancing – For speeds above 1000 RPM, ensure the joint is balanced

6. Bore fit – Use H7 shaft tolerance for best concentricity

7. Speed recommendation – Use at ≤50% of maximum rated speed for optimal life

9. Selection Checklist

• □ 

  Configuration: WSP – telescopic universal joint

• □ 

  Bearing type: Sliding (1000 RPM) or Needle (4000 RPM)

• □ 

  Material: 40Cr alloy steel (standard) or 304/316 stainless steel

• □ 

  Finish: Black oxide, polished, chrome, nickel, or sandblasted

• □ 

  Bore: H7 tolerance – match your shaft diameters

• □ 

  Bore option: Keyway, hexagon, square, or spline

• □ 

  Length: Specify Lmin and travel (S)

• □ 

  Angle: ≤30° for continuous use (45° limit per joint)

• □ 

  Speed: ≤50% of max rated speed for optimal life

10. Conclusion

The WSP telescopic universal joint coupling from Apex Coupling offers the perfect combination of angular misalignment compensation, axial length adjustment, and high-speed capability for demanding industrial applications. With 40Cr construction, sliding or needle bearing options, 45° angular flexibility, H7 bore precision, and hardened components, it is the ideal solution for packaging machinery, woodworking equipment, multi-spindle drills, and general automation.

👉 Need a telescopic universal joint for your application? Contact us with your configuration, bearing type, and length requirements.