Customer Case
P4-Class Extra-Large Paired Angular Contact Ball Bearings
Enable High-Precision Machining for Internal Milling Cutter Heads
Several years ago, we received a customization request from a high-precision machine tool manufacturer to design and produce dedicated precision bearings for its internal milling cutter head spindle system. The machine tool is mainly used for internal milling of precision components and places extremely high requirements on spindle rotational accuracy, rigidity, and long-term dimensional stability. The customer clearly required that the bearing accuracy reach P4 class and that accuracy retention remain reliable under long-term continuous machining conditions.
Project Background
High-Precision Internal Milling
High-Precision Internal Milling Places Extremely Demanding Requirements on Spindle Bearings
The customer has long been engaged in the manufacture of high-precision machine tools, with its equipment mainly used for internal milling of precision components. The internal milling cutter head spindle system is the core moving component of the machine tool, while the bearings are the key support units of the spindle system. Bearing rotational accuracy, rigidity, and long-term dimensional stability are directly transmitted to the rotational accuracy of the cutter head and are ultimately reflected in the surface quality and dimensional accuracy of the machined workpiece.
The customer clearly required that “bearing accuracy must reach P4 class, and accuracy retention must remain reliable under long-term continuous machining conditions.” These requirements mean that the bearings must not only achieve high accuracy at assembly, but also resist accuracy degradation during long-term operation and maintain stable performance.
02 · Technical Challenges
The Dual Test of P4-Class Accuracy and Long-Term Stability
Micron-Level Runout Control
P4 class is a high-precision bearing grade. Radial runout error must be controlled within 2–4 μm, and axial runout error within 5–7 μm. This means that every stage, from material selection to machining and manufacturing, must achieve micron-level precision.
Accuracy Retention During Long-Term Operation
However, high accuracy at the time of factory release alone is not sufficient to meet the customer’s long-term operating requirements. During service, slight dimensional changes may occur due to the release of residual stress and the transformation of retained austenite, causing the bearing to gradually lose accuracy.
03 · Customized Solution
Three-Dimensional Customization from Structure and Heat Treatment to Precision Manufacturing
In response to the customer’s demanding requirements, we provided a customized solution across three dimensions: bearing structural design, accuracy control, and heat treatment process.
Structural Solution
Paired extra-large single-row angular contact ball bearings.
Based on the load characteristics, installation space, and accuracy requirements of the internal milling cutter head, we adopted a structural solution using paired extra-large single-row angular contact ball bearings.
Single-row angular contact ball bearings can simultaneously accommodate radial loads and axial loads in one direction. When two bearings are paired in the specified arrangement, they can accommodate axial loads from different directions and improve the support rigidity and overturning-moment resistance of the bearing system, making them more suitable for applications such as internal milling cutter heads that require high rotational accuracy and combined-load capacity.
During the product design stage, our technical team comprehensively analyzed the internal bearing structure, contact angle, pairing arrangement, clearance or preload condition, and ring fits, so that the two bearings would form a coordinated and stable support system after installation.
Heat Treatment Process
Two Additional High-Temperature Stress-Relief Tempering Cycles to Ensure Long-Term Dimensional Stability
For extra-large P4-class precision bearings, conventional heat treatment alone is difficult to fully satisfy the requirements for long-term dimensional stability. After quenching and preliminary machining of the bearing rings, residual stresses may remain within the material. As temperature and load change during subsequent machining, storage, or equipment operation, these residual stresses may gradually be released, causing slight changes in ring dimensions or geometric accuracy.
To reduce this risk, in addition to the conventional heat treatment process, we applied two additional high-temperature stress-relief tempering cycles to this type of product. By reasonably setting the additional tempering temperature, holding time, and process stages, residual stresses within the rings are further released, the stability of the material structure is improved, and a more stable machining basis is provided for subsequent precision grinding and finished-product accuracy control. This process measure is one of the key stages in achieving high accuracy and high stability for this project.
Precision Manufacturing
P4-Class Grinding and Pairing Control to Ensure Micron-Level Accuracy and Uniform Load Distribution
To ensure that the bearings meet P4-class accuracy requirements, we strictly controlled every stage from heat treatment and precision grinding to paired assembly.
For single-row angular contact ball bearings used in pairs, meeting the accuracy requirement for each individual bearing is only the foundation; dimensional consistency and the pairing condition between the two bearings are equally important. Therefore, on the basis of finished-product inspection, we further implemented selective matching and pairing control to ensure uniform load distribution after installation and to prevent pairing deviations from affecting the rotational accuracy of the cutter head.
04 · Project Results
On-Time Delivery, Mass-Production Quality Satisfies the Customer
The customized P4-class precision bearings for the internal milling cutter head were successfully delivered on schedule , and the customer was very satisfied with the quality of our mass-produced products.
The successful delivery of this product once again verified our technical strength in the field of high-precision machine-tool bearings. From material selection to accuracy control, from the two additional tempering processes to strict factory inspection, every stage was based on “meeting the customer’s ultimate pursuit of accuracy and stability.”
Engineering Capability
Precision and Stability
Full-Chain Customized Engineering Capability
From P4-class accuracy of a single bearing, to paired-system rigidity, to long-term accuracy retention and batch consistency
P4-Class Precision
Paired-System Rigidity
Long-Term Accuracy Retention
Batch Consistency
Engineering Consultation
Custom High-Precision Machine-Tool Bearings
Do you also have customization requirements for high-precision machine-tool bearings? Contact us, and we will provide professional technical evaluation and customized solutions.