Asquith Butler Launches Two 6-Axis Mill-Turn Centers

The addition of turning capability to Asquith Butler's super high precision, travelling gantry, vertical spindle machining centres and travelling column, horizontal spindle machining centres has resulted in the introduction of two new, large capacity, 6-axis mill-turn machining centres, called STARTURN-VTG (Vertical Turning Gantry) and POWERCENTRE-500 MT respectively.

Availability of the former machine was announced during MACH 2012. The latter was on show for the first time at the company's open house, held at its Brighouse HQ and technical centre during the first week of December 2012.


The POWERCENTRE-500 MT horizontal mill-turning centre represented a double first at the show. It not only made its debut, fitted with a 3-metre turning and positioning table, but also incorporated a new system for error mapping and compensation throughout the entire working envelope. The result was to increase by an order of magnitude the machine's already very high inherent positional accuracy.

The volumetric and thermal error compensation system, MCS/TEC, was developed by the University of Huddersfield's Centre for Precision Technology in close collaboration with Asquith Butler. Its open house marked the first time that this advanced iteration of the machine compensation system had been incorporated into any machine tool.

The POWERCENTRE-500 MT mill-turn centre offers 6-axis machining advantages for applications where a horizontal spindle is preferable, although a wide choice of indexing, servo and angle heads means that the user is by no means restricted to horizontal work.

The machine demonstrated had an X-axis of 8 metres, a vertical Y-axis of 2 metres and Z-axis ram traverse of 1.5 metres, with cutting and rapid feed rates up to 10 m/min and 24 m/min respectively. Two rotary axes were provided by the 360-degree C-axis ram and a 220-degree A-axis head, both of which can be indexed in one-degree increments or servo operated, enabling everything from 5-sided machining to fully interpolative 5-axis profiling.

Stepless speeds up to 3,000 rpm were provided by a 37/43 kW spindle (although options deliver up to 20,000 rpm). The advanced specification includes an 80-station tool magazine with ATC, through-spindle and external flood coolant, a Siemens Sinumerik 840DSL control system and Sinamics servo drives.

The sixth axis was in the form of a 3-metre diameter, 30-tonne capacity, 60 kW turning and positioning table, capable of up to 100 rpm and delivering 25,000 Nm of torque. It incorporated the latest Siemens liquid-cooled permanent-magnet spindle motor technology, with rotary positioning feedback provided by a Renishaw RESD high-resolution, non-contact measuring system. Equally high accuracy is achieved when turning as during prismatic machining operations.

Tables of 4 or 5 metres diameter may also be specified, according to the size of the machine and customer preference. Machining centres already in the field may be retrofitted with the new table to extend production flexibility.


The STARTURN-VTG range of vertical machining centres announced earlier in the year can be similarly equipped with any of these tables, as well as the MCS/TEC system of error compensation. The machine is aimed primarily at the nuclear, oil, gas and renewables industries internationally, as well as the marine and defence sectors.

Linear axis travels range from 3 to 30 metres in X, 3 to 6 metres in Y, and 1 to 3 metres in Z. Cutting feed rate is up to the rapid traverse of 20 m/min, maximising metal removal and ensuring short idle times.

Automatic exchange of multiple milling heads, 50 kW of spindle power and speeds from 3,000 to 12,000 rpm allow rough, semi-finish and finish milling, according to the type of head chosen.

The rotating ram allows up to eight Capto C6 or C8 turning toolholders to be mounted on a turret-type attachment to suit the machining application, avoiding manual intervention for tool change. Positioning and clamping is achieved using a Hirth coupling and four pull studs, allowing high metal removal rates.

If more turning tools are needed to complete a cutting cycle, the requirement is met by automatic exchange of the turning head or individual tools. Turning tool attachments to accommodate long bars for internal boring are also available.

The chain-type magazine for automatic exchange of prismatic machining cutters and turning tools has 60, 80, 100 or 120 pocket options. Coolant delivery to the cutting area is by external flood as well as an advanced, high pressure, internal through-the-spindle system.

Positional feedback to the Fanuc, Siemens or Heidenhain control is via linear scales and high resolution rotary encoders to ensure utmost precision.

As with the POWERCENTRE-500 MT, behind the STARTURN-VTG's intrinsic, long-term, micron-level accuracy and repeatability, despite its large size, are high levels of stiffness and vibration damping designed into the structure using the latest finite element analysis techniques. Further features ensuring close tolerance machining include optimised column and gantry structures, and generously proportioned guideways.

On behalf of:    Asquith Butler Ltd,

    Spring Vale Industrial Estate, Elland Road,

    Brookfoot, Brighouse, West Yorkshire, HD6 2RA, UK.

    Tel: +44 (0)1484 726620.  Fax: +44 (0)1484 718708.

    Contact: Paul Hinchliffe, Managing Director.



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