CNC Onsite sets new standards in flange precision for offshore wind

Vejle, Denmark, 10 September 2025 — As offshore wind turbines grow larger, achieving precise flange connections is increasingly critical. CNC Onsite, a precision machining expert, has now demonstrated consistent sub-millimeter flatness across multiple major projects —transition-piece flanges at CS WIND Offshore and bottom flanges on Vestas towers manufactured at Welcon—well below the industry standard of 2.5 millimeters. This proven precision enhances structural integrity, reduces maintenance, and supports longer turbine service life.

Tolerance of below 1 millimeter

At CS WIND Offshore, a leading supplier of offshore wind turbine foundations in Aalborg, Denmark, the company’s “Goliath” precision milling machine has been employed on transition-piece flanges, achieving a global flatness tolerance of below 1 millimeter. The in-house developed machine delivers exact contact surfaces for bolted connections, enhancing reliability for offshore foundations.

“The tolerances we are achieving demonstrate that even the largest transition-piece flanges can be prepared with consistent, high precision,” says Soren Kellenberger, Sales Director at CNC Onsite.

For Welcon’s production of Vestas’ 15 MW V236 towers, Goliath has been applied to bottom-tower flanges since spring, reaching a flatness as low as 0.21 millimeters, far exceeding standard requirements. Across both projects, CNC Onsite has proven that Goliath consistently delivers tolerances well below the 2.5-millimeter industry benchmark, eliminating the need for heat straightening and reducing post-production adjustments.

“By integrating Goliath directly into production, manufacturers can streamline production, maintain consistent tolerances across every flange, and engineers gain greater flexibility in design—including bolt sizing and arrangement. We are convinced that this approach will become a standard part of future turbine manufacturing,” says Kellenberger.

Goliath is fully adaptable for flanges ranging from 6.5 to 10 meters in diameter and can handle flat, tilted, and double-tilted surfaces, as well as features such as gasket grooves. Its precision enables manufacturers to meet increasingly strict flatness requirements, supporting turbine performance and operational reliability. 

Learn more at HUSUM WIND 2025
CNC Onsite will showcase Goliath and its flange machining capabilities at HUSUM WIND, the leading German-speaking wind-energy trade fair, from 16 to 19 September 2025 in Husum, Hall 3, stand 3C31. Visitors can see how the integrated machining solution establishes a new benchmark for precision across both transition-piece and bottom-tower flanges. 

About CNC Onsite

Headquartered in Vejle in Denmark, CNC Onsite designs and delivers high precision mobile machining for wind turbines including offshore foundations. Machinery built by CNC Onsite are designed to be flexible using its proprietary "building blocks" approach, which means machinery can be built to match a range of tasks. CNC Onsite serves the onshore and offshore wind energy sector delivering as standard solutions: machining of large diameter steel flanges and blade root ends; specialized repair services covering yaw ring, inserts in blade root, rotor lock, generator shaft, bearing housing and threaded holes. Removal and replacement of worn and broken bolts round off the offering.

Website: www.cnconsite.dk