Sandvik Coromant Introduces Silent Tools™ Boring Bar for Finnish Manufacturer

Sandvik Coromant Launches World's Largest Boring Bar at 11,000 mm Length and 600 mm Diameter

Sandvik Coromant, the machine tools specialist and one of the pioneers in precision engineering, has recently introduced the world’s largest boring bar. This engineering marvel incorporates impressive dimensions, measuring nearly 11,000 mm (11 m) in length and 600 mm in diameter. Developed to cater specifically to the machining needs of Häkkinen Group Jyväskylä unit, a Finnish engineering company, this lathe tool is destined for the production of meticulous metal components spanning various sectors, including offshore oil and gas, power transmission, and renewable energy.

As one of the key divisions within the global industrial engineering group Sandvik, Sandvik Coromant focuses on producing cutting-edge tools, machining solutions, and knowledge that set industry standards and drive innovations essential for the metalworking sector. Through robust educational support, substantial investment in research and development, and steadfast customer partnerships, Sandvik Coromant aims to advancing machining technologies.

The unique challenge presented to Sandvik Coromant by Häkkinen Group Jyväskylä unit involved the machining of a confidential component with critical dimensions. Although the exact nature of the component remains undisclosed due to confidentiality agreements, it is noteworthy for its substantial size—measuring 800 mm in diameter and extending to an impressive length of 12,000 mm (12 m). Moreover, the machining process involves working on both sides of the component.

The pivotal tool required for this intricate task is a boring bar, a tool used in machining operations to precisely enlarge and refine the diameter of an existing hole in a workpiece. Boring bars offer superior precision, accuracy, and smoothness compared to holes created by drilling, which may result in rougher finishes. In this case, the specific challenge demanded a boring bar of unprecedented dimensions. The large size is crucial for facilitating deep and precise internal turning operations, surpassing the capabilities of standard-sized bars.

Vibrations Reduction

Häkkinen Group Jyväskylä unit sought assistance from its partner ŠMT, a prominent producer of high-precision machines, based in the Czech Republic, known for horizontal boring and milling machines and lathes. Recognizing the need for a specialized machine tooling expert to provide a boring bar with exceptional dimensions for a unique project, ŠMT reached out to Sandvik Coromant CZ, located in the Czech Republic.

Sandvik Coromant CZ, a renowned producer of boring bars, especially those with anti-vibrational properties, was approached to support the development of an exceptionally large boring bar. Vaclav Faber, Project Engineer at Sandvik Coromant CZ, highlights the importance of reducing vibrations in a boring bar, as it is critical for ensuring precision and surface finish quality in machining operations.

The significance of minimizing vibrations lies in preventing inaccuracies, tool wear, and potential compromises to the workpiece’s integrity—concerns that were particularly relevant given the extensive scale of Häkkinen Group Jyväskylä unit’s machining operation. By reducing vibrations, the boring bar maintains stable and controlled cutting conditions, leading to increased productivity, extended tool life, and superior surface finishes.

In addition to vibration reduction, ŠMT had other specific requirements for the boring bar. Häkkinen Group Jyväskylä unit needed a tool that seamlessly integrated with its existing machinery while pushing the boundaries of turning operations. Compatibility with ŠMT’s large lathe was also essential.

Enter Sandvik Teeness in Trondheim, Norway, selected for its long-standing reputation as a market leader in the development and production of boring bars, dating back to the 1960s. The team’s expertise was instrumental in meeting the stringent requirements set forth by ŠMT and Häkkinen Group Jyväskylä unit for this ambitious project.


The steel bar incorporates a critical element known as a “damper,” composed of heavy metal and employed to mitigate vibrations. Dampers, which are not commonly found in machinery or structures, are secured within special rubber rings to effectively reduce or absorb vibrations.

Another essential component of the bar is the Coromant Capto® tool holder, positioned at the front of the bar. This tool holder is responsible for securing the cutting inserts necessary for machining the workpiece. The Coromant Capto® is specifically designed to streamline setup and tool change times, leading to significantly enhanced machine utilization. Its purpose is to facilitate stable and reliable machining processes.

Vaclav Faber emphasizes the practicality of the tool holder, particularly in multi-task machines. The Coromant Capto® allows for the assembly of tools with varying lengths and design characteristics, irrespective of the machine interface. Additionally, it fulfills Häkkinen Group Jyväskylä unit’s requirement for a versatile boring bar that can be employed across a diverse range of industrial setups.

The Boring Bar has been designed to meet the Machining Requirements of Häkkinen Group Jyväskylä unit, a Finnish Engineering Company

Comprehensive Testing Process

Specialists from Sandvik Teeness conducted extensive frequency measurements on-site to evaluate the effectiveness of the integrated dampening adapter within the bar. The bar underwent rigorous testing on a large CNC lathe, subjected to multiple trials in three distinct applications—roughing, finishing, and profiling—each time utilizing different cutting data.

During the tests, the tool operated with a maximum allowed overhang of 10-times the diameter (10 x D), a recommendation aimed at minimizing vibrations and ensuring optimal stability and accuracy. Sandvik Coromant’s Silent ToolsTM boring bars, recognized for operating with minimal vibrations, are typically utilized with long tool overhangs, emphasizing the importance of rigid clamping. Cylindrical boring bars, like the one in question, should always be clamped in a split sleeve holder with a minimum clamping length of 4 x the bar diameter.

The cutting data used was initially based on recommendations from the CoroPlus® Tool Guide software platform, which were subsequently adjusted during the testing phase. For roughing applications, the bar consistently ran with a cutting speed (vc) of 100 m/min and feed-per-revolution (fn) of 0.4 mm/rev. The load on a boring bar is influenced by factors such as the depth of cut (ap), feed, and workpiece material. Maintaining sufficient ap and fn is essential to avoid vibration during cutting, while excessively high ap and fn values can lead to tool deflection.

To address these considerations, the ap was modified for testing purposes. Vibration was observed at an ap of 5.6 mm, and performance was limited at 4.5 mm. Ultimately, a depth of cut of 3.5 mm was identified as the recommended setting.

In finishing and profiling applications, the bar operated at a vc of 110 m/min and ap of 0.5 mm each time. The fn was adjusted, with 0.25 identified as the optimal and recommended setting, resulting in a roughness average (Ra) of 3.4.

Vaclav Faber, Project Engineer at Sandvik Coromant CZ, notes, “Based on the test results, Sandvik Coromant’s specialists were able to recommend cutting data parameters and inserts to ŠMT.”

Jaroslav Šuga, Global Account Manager at Sandvik Slovakia, adds, “Regular meetings with the Sandvik Teeness production team were held to discuss the bar’s delivery time and all details concerning manipulation, transport, and logistics. Success was possible because we worked together with ŠMT’s designers, technologists, the production team in Norway, and all people involved in the sales process.”

Continued Investment in Precision Machining

Sandvik Coromant has not only pioneered the development of an extraordinary-sized boring bar but has also provided Häkkinen Group Jyväskylä unit with an invaluable tool for precision machining across various sectors in its workshop. The world’s largest boring bar, now operational in Häkkinen’s facility, has made a significant impact, prompting ŠMT to consider further investments in slightly smaller boring bars from Sandvik Coromant for the machining of components with slightly reduced dimensions.

Vaclav Faber notes, “The world’s largest boring bar remains testament to Sandvik Coromant’s unwavering commitment to innovation and precision in machining applications.” This acknowledgment underscores the pivotal role played by Sandvik Coromant in pushing the boundaries of innovation and delivering solutions that address the unique machining needs of its clients.


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