Making untraceable repairs to priceless timepieces over two hundred years old requires skill, infinite patience and precision. Bringing repairs to as new condition, one of the UK’s most skilled clock and watch restorers uses a Swiss made milling machine recently upgraded with ABB variable-speed inverter drives (VSDs) to control the machines speeds.

Rare Aciera F1 milling machine

James Chadburn, a member of the British Horological Institute, repairs and specialises in the restoration of clocks that can be up to 400 years old, making and installing new parts that exactly match original components. For this, he purchased a rare Aciera F1 Swiss-made milling machine designed to achieve the high accuracies of around 0.0004 mm demanded in clock and watch making.

The first challenge was running this three-phase machine from the single-phase supply in the workshop. As well as its use in converting the power input from single-phase to three-phase, the main VSD is used to drive the milling head at different speeds to match the work being done.

The Aciera F1 has two speed selection dials, one with 125, 250 and 500 rpm and the other with 1,000, 2,000 and 4,000 rpm. The milling machine is linked to the VSD so selecting the speed on the Aciera selects the appropriate speed from the VSD.

Accurate speed control improves finishing

Says Chadburn: “If I am cutting brass then I would select 4,000 rpm, certainly nothing under 3,200 rpm. With multi-tooth cutters, most of the finishing of the piece is achieved during the cut itself, doing up to 80 percent of the polishing work. Controlling the speed in this way means I can accurately replicate wear on a component, making it look 250 years old. For hard steel, the VSD allows me to slow the milling machine right down – if it is too fast, it can destroy the cutters or overheat and scorch the component.”

One of the drives supplies the three-phase power for the milling machine as well as providing speed control, while the other simply provides three-phase power to the coolant pump. ABB machinery drives are intended for use by the machine building sector and are available in ratings of 0.37 kW to 22 kW. They are designed to be quick and easy to install and commission, with Chadburn’s installation taking less than a day.

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