n a twin-turret, twin-opposed-spindle bar automatic, three tools can cut simultaneously and accurately thanks to a 'world-first' use of a kinematic drive to replace turret compound slide.

A 'world first' is claimed by German turning machine manufacturer, Index, for its new C-Series of twin-turret, twin-opposed-spindle bar automatics, which see the disappearance of the conventional compound slide for turret movement. In its place is a patented guideway system employing two plates sliding directly over the 75 deg slant bed. The turret is mounted on the front plate while the rear retaining plate is kinematically driven in X and Z.

The advantage of this system is that the distance between the turret centreline and the point, at which it is driven is shorter than for a compound slide, making it several times stiffer.

The result is greater rigidity and better damping, leading to higher accuracy machining, even for strenuous applications involving intermittent hard turning and reaming.

Tool life is also extended.

The turret and drive plates are fitted with ceramics-coated, hardened tool steel strips at top and bottom which slide over a third plate of surface-hardened cast iron fitted into the bed, the latter plate being effectively sandwiched between the other two.

The parallel kinematic drive to the rear plate is effected by three ballscrew-actuated rods at the back of the machine, two vertical and one horizontal.

Glass linear scales provide positional feedback.

The system is faster than a compound slide, allowing rapid traverse rates of 25m/min in X and 50m/min in Z, and acceleration of 1G.

As a result, the manufacturer says that the lathe reduces cycle times by between 10 and 30% compared with other twin-turret, twin-spindle lathes on the market.

The compact turret design contributes to a small machine footprint, allowing four C-Series lathes to fit in the space occupied by three equivalent turning machines from other manufacturers.

Additional space in the working area also makes for better access and chip evacuation.

Both turrets are equipped with a 70mm Y-axis for even greater versatility when mill/turning highly complex components.

Available in two sizes through sole UK agent, Geo Kingsbury Machine Tools, the Index lathes are called SpeedLine C42 and C65, the numbers representing the maximum bar capacity in millimetres.

The 6.5 tonne machines are being built at the rate of one per day at the Index factory in Esslingen, where an 18-stage flow line and adjacent turret assembly line have been set up at a cost of EUR 1 million.

A full C-axis and 27kW of spindle power are provided at both ends, delivering top speeds of 6,300 rev/min and 5,000 rev/min for the respective models.

Clearance between the 140/160mm diameter chucks for between-centres work is 615mm.

The patented, air-cooled spindles are manufactured in-house, allowing close quality control to be maintained.

The opposed spindle is not only powerful but also has the unusual option of 150mm of X-axis movement in addition to 600mm of longitudinal travel.

By electronically coupling the movements with the X/Z motion of a lower, double-sided, 24-tool turret (optionally available in place of the single-sided version), Index provides the ability to have three tools in cut simultaneously.

This is achieved by deploying the upper 12-station turret and the left face of the lower turret to machine a component in the left hand spindle while the 'slave' right hand spindle follows the latter turret around, enabling a parted-off component to be machined using the right face of the lower turret.

In other words, the X- and Z-axis movements of the lower turret resulting from the cutting cycle in the left hand spindle are continually allowed for in the programmed movements for back-working.

Driven tool capacity is 8kW/6,000 rev/min, available at all 12 stations of each turret.

Noteworthy also is polygon generation using a head mounted directly on the counter spindle rather than on a turret, ensuring vibration-free machining and hence greater accuracy and longer tool life, especially when cutting alloy steels.