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Wind power

Best practice - Connecting ring

The tower of the wind turbine can be as tall as 90 metres and carries the nacelle and the rotor. Most large wind turbine towers come with tubular steel sections of 20-30 metres.

The tube sections are bolted together by connecting rings – one at each end of the section. Typically six to eight connecting rings are used in a wind turbine tower.


Common connecting ring

  • Forged (seamless) or made from bars with a welded joint
  • Typical material: Low carbon steel (CMC01.2).
  • 6-8 rings/tower
  • Diameter of 3,000 – 9,000 mm
  • Typical thickness: >100 mm
  • Numerous holes
  • Machining operations: turning, drilling

Machining operation overview:

Back to connecting ring

1. Turning – Roughing

    • Outer diameter (OD)
    • Inner diameter (ID)
    • Facing

2. Turning – Finishing

    • Outer diameter (OD)
    • Inner diameter (ID)
    • Facing

3. Drilling


  1. Turning - (OD)
  2. Turning - (ID)
  3. Turning - Facing
  4. Drilling


  • Diameter: 4,000 mm
  • Material: Low carbon steel (CMC01.2). Forged skin.
  • Machine: Vertical lathe
  • Coolant: Dry machining
  • Production rate: 9,600 components per year
  • Objective: Productivity increase


Sandvik Coromant Competitor​
Holder​ PCLNR 3232-19​ PCLNR 3232-19​
Insert​ CNMM 190624-HR​ CNMM 190624 R7​
Grade​ GC4325​
Depth of cut (ap)​ 10 mm​ 10 mm​
Cutting speed (Vc)​ 150 m/min​ 195 m/min​
Feed (fn)​ 1.33 mm/rev​ 0.85 mm/rev​


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​Turning - Roughing

The T-MAX® P concept encapsulates the contributions of productive turning. The geometries are carefully designed for perfect chip breaking. Metal removal at high feed and in dry conditions is made possible with state-of-the-art grades for your application.

To optimize productivity with better precision and stability – use Coromant Capto® tool holding system. The modular system is equally effective in turning, milling, drilling and boring.

The same cutting units and adaptors can be used in different applications and machines, which makes it possible to standardize on one tooling system giving substantial reduction of inventory.


Productivity increase: 19%

Time saved/year: 2,506 hours

Savings/year: € 178,358

CNMM 190624-PR​ CNMG 190616-PM​
Depth of cut (ap)​ 2-6 mm​ 1-5 mm​
Cutting speed (Vc)​ 150-200 m/min​ 150-200 m/min​
Feed (fn)​ 0.4-1.0 mm/rev​ 0.25-0.5 mm/rev​

Turning - Finishing​

A Coromant Capto holder is also the first choice for the finishing operation. Combine with a GC4215 grade for best productivity.

A CNMM 190624-PR will give you optimal productivity with high feed and good chip control. If your machine requires lower feeds however, a CNMG 190616-PM is recommended.

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  • ​Machine: Vertical machining centre, double spindle
  • Spindle interface: ISO 50 taper
  • Coolant: Internal coolant 10%
  • Number of holes per ring: 60
  • Production rate: 240,000 holes per year/4000 pieces per year
  • Objective: Productivity increase


Sandvik Coromant solution​ Competitor​
Hole diameter 45 mm​ 45 mm​
Hole depth​ 158 mm​ 158 mm​
Cutting tool​ 880-D4500L50-04​

880-0805W10H-P-LM 4024

880-080508H-C-LM 1044​

Cutting speed (Vc)​ 320 m/mm​ 250 m/mm​
Feed (fn)​ 0.12 mm/rev​ 0.1 mm/rev​



Just by exchanging a conventional drill with a CoroDrill 880, you can double the number of drilled holes in the same amount of time.

Its step technology gives outstanding cutting force balance, providing significant improvements on productivity as well as of the hole quality.

This, in combination with high performance grades makes it outstanding when it comes to rapid hole making.


Productivity increase: 53%

Time saved/year: 1,253 hours

Savings/year: € 100,156

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