The race is on for high-precision grinding

Father and son, Antoon and Randy Gevers at GRT-Tech in the Netherlands
Father and son, Antoon and Randy Gevers at GRT-Tech in the Netherlands

Before founding his company GRT-Tech in the Netherlands, Randy Gevers was successful in motorcycle racing for many years. However, his success story does not begin with him, but with his father Antoon Gevers, who not only inspired his son with a passion for engines and technology, but also enthused him for metalworking, and in particular grinding.

After years of working as grinders in the same company, the pair took the plunge into self-employment in 2016, when Antoon took early retirement. The first machine they purchased was a conventional grinding machine, with others following in short succession. Fittingly, the first customers came from KTM Motorcycles, as the Gevers had built up a large network through their own racing endeavours.

Today, customers from the aerospace, medical technology, tool and die, packaging industries and luxury yacht sectors trust the Gevers’ expertise. Among the demanding customers who value GRT-Tech's work are suppliers to the semiconductor industry.

"We could theoretically make a living on that work alone," Randy says. "But a company shouldn't get into dependencies and it's ultimately the variety of parts that makes the job appealing."

Internal grinding of a workpiece with a problematic material combination of copper and cast iron
Internal grinding of a workpiece with a problematic material combination of copper and cast iron

Materials processed at GRT-Tech range from steel, stainless steels, brass and copper to ceramics and plastics. Small batches of up to 50 pieces are common, as well as individual parts and prototypes. Antoon Gevers often manufactures special parts for motorcycles and classic cars that customers entrust to him based on his experience.

In a short while, Randy Gevers realised that for the machining of complex workpieces, e.g. for tool and mould making or medical technology, the limits of a conventional grinding machine are quickly met. For this reason, he purchased a used high-performance Kellenberger CNC universal cylindrical grinding machine – a Kel-Varia.

“We had a lot of requests for grinding complex workpieces right from the start,” says Randy. “But we could only accept about 10% of them. It couldn’t continue like that.” The decision in favour of a Kellenberger grinding machine was not a difficult one. Antoon and Randy Gevers knew and respected these machines from their former employment.

The Kel-Varia is a predecessor model of today's premium Kellenberger 1000 series. Its high static and dynamic rigidity and stability are decisive factors for high precision and great productivity. Hydrostatic guides in all main axes ensure high accuracies for grinding tasks with interpolating axes.

Non-circular grinding of Capto holders
Non-circular grinding of Capto holders

The B-axis has a direct drive. The turret grinding head thus swivels about three times faster and positions with an accuracy of less than one angular second. Particularly when machining requires the swivelling in of different grinding wheels, this reduces non-productive times and thus increases productivity.

As a result of this valuable experience, another Kellenberger grinding machine quickly found its way to GRT-Tech, a Kellenberger 100 universal internal and external cylindrical grinder.  

The Kellenberger 100 is available with centre widths of 1,000/600mm and centre height of 200mm and is designed for workpiece weights of up to 150kg. The high drive power of the grinding wheel ensures increased productivity, while the newly developed Z guide ensures high profile accuracy. The C-axis with direct drive brings higher accuracy for non-circular grinding.

Technical highlights of the machine include an innovative compact grinding head (10 grinding head variants), 11.5kW drive power, a 500mm wheel with speeds up to 63m/second, HF spindles for internal grinding (including diagonal and tandem arrangement), a collision-free universal head with three tools and one measuring position, and a new measuring probe arrangement without swivel mechanism for increased measuring accuracy.

The variety of workpieces for a wide range of industries makes the work interesting at GRT-Tech
The variety of workpieces for a wide range of industries makes the work interesting at GRT-Tech

Randy Gevers chose the centre width 1,000mm to be more flexible with part size, and a grinding head variant with two external grinding spindles, an internal grinding spindle and a tactile measuring head. The high-frequency spindle, with a speed range of 6,000 to 40,000rpm, has an internal coolant supply. The machine is equipped with a FANUC 31i CNC control, the matching software is provided by Kellenberger.

“I am fascinated by the machine's great reliable accuracy. But I consider my many years of experience to be the factor also that ultimately makes the difference for the customer. After all, a machine can't provide the advice on how best to manufacture a workpiece,” says Randy.

Challenging workpieces are part of the daily business at GRT-Tech, such as the current machining of a component with a material combination of copper and cast iron. The required roughness is < 0.15µm.

“We could even achieve 0.05µm, but that is not necessary in this application,” explains Randy. “Cast iron is a very porous, brittle material; the grindstone clogs very quickly and must be continuously dressed – but again not too often – it’s essentially a matter of finding the right balance.

Randy Gevers racing on his Aprilia 1,000cc motorcycle
Randy Gevers racing on his Aprilia 1,000cc motorcycle

“The more experience and intuition a grinder possesses, the more precise such a workpiece will be in the end. Which, incidentally, is very expensive due to the material combination and the upstream machining operations such as turning, milling and eroding. So, the grinding operation has to be right the first time.”

He concludes: “The more complex the workpiece, the higher the precision requirements, the greater the motivation for me to bring the workpiece to perfection.”

Kellenberger grinding machines are available from DF Precision Machinery in Lutterworth, the sole UK agent for all Hardinge Group brands.

DF Precision Machinery

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