Case Study: On-Site CNC Thread Milling for Offshore Wind Tower Flanges

Client: Sif Group
Industry: Offshore Wind Manufacturing
Location: Roermond, Netherlands
Services: In-Situ Machining, On-Site CNC Machining, Thread Milling

The Challenge

Following several successful in-situ machining projects on wind tower flanges, Reekie Machining was engaged by Sif Group, a leading manufacturer of offshore wind foundations, to support a late-stage design change.

As part of its manufacturing process, Sif procures fully machined flanges which are welded to rolled sections to form monopiles and transition pieces. After the flanges had been ordered, a change to the installation requirements meant that 16 of the 152 clearance holes in each flange had to be converted into M98 threaded holes, machined through the full 180 mm flange thickness.

Due to programme constraints, the machining had to be carried out on site at Sif’s Roermond facility. The scope involved:

• 95 flanges

• 1,520 M98 threaded holes

• Tight dimensional and thread tolerances

• Zero tolerance for non-conformance, with rejected flanges resulting in significant cost and schedule impact

The On-Site CNC Machining Solution

Reekie Machining proposed a controlled on-site CNC machining solution using its RTM100 CNC thread milling machine, specifically designed for large-diameter, deep threaded holes where accuracy and repeatability are critical.

To meet the demanding schedule, multiple machines were required to operate simultaneously. At the time of order—just four weeks before mobilisation—Reekie had only one RTM100 available.

Because Reekie designs and manufactures its own CNC machining equipment and control systems, additional RTM100 machines were rapidly built, commissioned, and deployed, allowing the project to proceed without delay.

Delivery

Multiple RTM100 machines and experienced in-situ machining specialists were mobilised to site, establishing a repeatable CNC thread milling process capable of maintaining consistent quality across all flanges.

Despite the size, depth, and volume of machining required, all on-site CNC machining works were completed:

• Within the agreed programme

• On budget

• Fully to specification

The Result

• 1,520 M98 threads machined by in-situ CNC machining

• Zero rejected flanges

• No disruption to welding or installation schedules

• High accuracy and repeatability across all components

Why Reekie Machining

This project highlights Reekie Machining’s expertise in:

• In-situ machining for large offshore wind components

• On-site CNC machining in active manufacturing environments

• Rapid scaling of capacity through in-house machine tool manufacture

• Delivering precision machining solutions for time-critical wind energy projects