on-site machining

Reduce costs, reduce maintenance time and minimize downtime
by using CNC Controlled on-site machining. 


Machining on-site at the highest accuracy.

Cutter drive shafts

Due to the extreme forces exerted on the cutter shafts by dredging, it can in some cases occur that the special bolts with which the cutter drive shafts are connected or secured together, loosen. Oversized line boring of this specific hole on-site is the simplest solution. An oversized bolt will then be placed in this hole to solve the problem.

However, the simple way is not always the right way. By only machining this specific hole larger, the existing accuracy of the hole pattern is gone and the cutter shaft is no longer interchangeable. The shafts will therefore always have to return to this specific position in the line. The existing hole pattern has been processed with such precision that the shaft or shafts of a cutter dredger are interchangeable. All holes are precisely made within 0.02 mm in diameter, on pitch circle, cylindricity, squareness, and concentricity.

The possibly one damaged hole is not round. Where is the exact centre of this specific hole? And more importantly what is the position in relation to the centreline of the shaft and the pitch circle?

On-site oversized machining of one specific hole is relatively easy, by placing a boring bar in this hole. The boring bar is aligned to this hole and machined oversized. However, when you work one damaged hole, the damaged hole is the reference. As a result, the accuracy in squareness and concentricity of the shaft is gone. This hole is no longer in line with the other existing holes. As a result, the shaft is no longer interchangeable.

Gerben van Leeuwen Worldwide Technical Services has developed a machine with which all holes or one specific deviated can be machined with such an accuracy, that this hole or holes are machined at its original position(s) and this shafts remains interchangeable.

This machine has an accuracy of 1 arc second (0.000278 mm), which is within the required tolerance of the entire cutter shaft.

The hole pattern, pitch circle, squareness and concentricity are all machined within 0.02 mm with the CNC controlled machine. This ensures that when one or more holes have to be machined, the shaft remains interchangeable with the other shafts in the cutter dredger.

This involves centreline compensation. When the machine has been measured towards the centreline of the shaft, it is automatically compensated and placed in the centre of the centreline of the shaft, or the hole pattern.

A big advantage is that when all holes are different, and therefore this shaft or these shafts actually need to be replaced, this is not necessary after machining with this machine. This way a lot of costs can be saved. All holes are machined oversized. Oversized bushes are then placed with nitrogen, after which these bushes are machined again to the original dimensions. And even more important, 100% back in there original position and measurements.

In short, no purchase of a new shaft or shafts. This reworked shaft can be in production for years to come.

More information about
cutter drive shafts?

Worldwide operative in

  • Offshore
  • Wind Industry
  • Maritime
  • Dredging
  • Power Generation

Cold Metal Transfer Welding

Cold Metal Transfer welding is a modified MIG welding ­process based on short-circuiting transfer process.

This process differs from MIG/MAG welding process only by the type of mechanical droplet cutting method not ­previously encountered. During welding, temperature variations in welds and parent metals have important effects on material characteristics, residual stresses as well as on dimensional and shape accuracy of welded products.

Cold Metal Transfer provides controlled method of ­material deposition and low thermal input by incorporating an ­innovative wire feed system coupled with high-speed digital control. The wire feed rate and the cycle arcing phase are ­controlled to realise sufficient energy to melt both the base material and a globule of filler wire.

There are two main features of the CMT process: one is at the point of short circuit with low current corresponding to a low heat input, another is the short circuit occurrence in a stable controlled manner.

The big difference is in the wire feed. Rather than continuously moving forward into the weld pool, with CMT the wire is retracted the instant current flows. That breaks the arc. The metal droplet detaches from the filler and fuses with the – still molten – base metal. Then the wire moves forward to create another arc, and all this happens many times each second. The difference from conventional MIG welding is fairly subtle, although it needs a lot of sophisticated control technology. The benefit is that it reduces heat input signi- ficantly. The developer of CMT welding, Fronius, describes it as, “Hot, cold, hot, cold, hot cold.”


Cutter Drive Shafts
Pump Housings
Transitioning Pieces
Turbine casing

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Gerben van Leeuwen

More than 20 years of experience in on-site machining worldwide not only managing this particular specialism. But because of his great passion for the job and quality, still performing it by himself. Therefor it makes him unique comparing him to others.