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SK40 LBK1 to LBK4 Boring Holders: Specifications, Compatibility & Applications

Author : Surya makeyoueasy | Published On : 11 Nov 2026

Introduction

Accurate internal boring requires a stable connection between the CNC machine spindle, tool holder and boring head. SK40 LBK1 to LBK4 boring holders provide a modular connection for compatible LBK boring heads, supporting different boring diameters and machining requirements.

Understanding their specifications, connection sizes and holder lengths helps machinists select the right combination for reliable CNC boring operations.

What Are SK40 LBK Boring Holders?

SK40 LBK boring holders are tool holders designed to connect compatible LBK-series boring heads to an SK40 machine spindle.

The SK40 taper fits the machine spindle, while the LBK connection at the opposite end accommodates a matching modular boring head. This arrangement allows operators to use different boring-head sizes with compatible holder systems.

Important: SK40 identifies the spindle-side taper interface, whereas LBK1, LBK2, LBK3 and LBK4 identify different modular connection sizes. They are not interchangeable without checking the matching interface dimensions.

Specifications of SK40 LBK1 to LBK4 Boring Holders

The following table shows representative specifications from LBK-compatible tooling catalogues. Actual dimensions and available lengths can vary by manufacturer.

 

Note: Boring ranges refer to representative compatible boring-head models, not the SK40 holders themselves. Confirm all dimensions and model-specific specifications with the manufacturer before ordering.

Understanding the LBK Sizes

1. SK40 LBK1 Boring Holder

LBK1 is the smaller connection size in this group. It is commonly paired with compatible smaller boring heads for applications involving relatively small internal diameters.

2. SK40 LBK2 Boring Holder

LBK2 provides a larger modular connection than LBK1. It can be used with compatible boring heads for medium-small boring ranges.

3. SK40 LBK3 Boring Holder

LBK3 offers a larger connection interface and supports compatible boring heads for medium-diameter internal machining.

4. SK40 LBK4 Boring Holder

LBK4 is the largest connection size among these four options. Its larger interface supports compatible boring heads for comparatively larger boring diameters.

Key Features of SK40 LBK Boring Holders

1. Modular Connection System

The LBK interface allows compatible boring heads to be mounted on the holder. This modular arrangement helps machining workshops configure tooling for different boring requirements.

2. SK40 Spindle Compatibility

The SK40 taper is designed for machines with a matching spindle interface. Confirm the applicable standard, such as DIN 69871, and the correct retention knob before installation.

3. Multiple Holder Length Options

Different holder lengths help accommodate varying machining depths and accessibility requirements. Select the shortest practical length that provides sufficient clearance and reach.

4. Compatibility Across Boring Head Sizes

LBK1 to LBK4 provide different connection dimensions for matching boring heads. Correct interface matching is essential for secure mounting and stable machining.

Applications of SK40 LBK Boring Holders

When paired with compatible boring heads, SK40 LBK holders can support:

  • Internal boring: Enlarging existing holes to the required diameter.

  • Precision hole machining: Preparing internal surfaces to meet dimensional requirements.

  • Step boring: Machining different internal diameters in suitable component designs.

  • CNC machining: Boring operations on machining centres with compatible SK40 spindles.

  • Production machining: Repeated internal machining operations using modular tooling combinations.

The final application depends on the boring-head design, cutting insert, workpiece material and machining conditions.

How to Select the Right SK40 LBK Boring Holder

1. Identify the LBK Connection Size

Check whether the boring head requires LBK1, LBK2, LBK3 or LBK4. The connection must match the holder exactly.

2. Check the Required Boring Diameter

Select a compatible boring head based on the finished hole diameter and its adjustment range.

3. Choose the Correct Holder Length

Consider the machining depth, workpiece clearance and tool accessibility. Excessive tool overhang can increase vibration and reduce machining stability.

4. Verify SK40 Spindle Compatibility

Confirm the spindle taper standard, retention knob specification and machine requirements before fitting the holder.

5. Consider Machine Rigidity

Ensure that the machine, workholding and tool assembly provide sufficient rigidity for the planned boring operation.

Common Compatibility Checks

 

Why Choose MakeYouEasy for CNC Tool Holders?

MakeYouEasy helps machining professionals explore CNC tool holders, boring tools, cutting inserts and machining accessories. Selecting the correct holder and matching boring head is important for achieving a secure tool connection and consistent machining results.

Conclusion

SK40 LBK1 to LBK4 boring holders provide modular tooling connections for compatible CNC boring heads. Each LBK size has different interface dimensions and supports different boring-head configurations. By checking spindle compatibility, connection size, holder length and boring range, machinists can select a suitable holder for their machining requirements.

Explore CNC tool holders and machining accessories at MakeYouEasy.com.

FAQs

1. What are SK40 LBK boring holders used for?
They connect compatible LBK-series boring heads to CNC machines with matching SK40 spindle interfaces.

2. What is the difference between LBK1, LBK2, LBK3 and LBK4?
They have different modular connection dimensions and are designed for matching boring-head sizes.

3. Are SK40 LBK1 and LBK2 interchangeable?
No, their connection dimensions differ, so the holder must match the boring head’s LBK interface.

4. How do I choose the correct SK40 LBK holder length?
Choose a length that provides the required machining reach and clearance while minimising unnecessary overhang.

5. Can SK40 LBK holders be used on any CNC machine?
They can be used on machines with a compatible SK40 spindle interface and the correct retention knob configuration.

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