Starrag has already been meeting requirements such as these for a few years, for example with the STC 800, the smallest version of the 5-axis machining centre range. It is offered as an MT version with a rotary table to meet all of the demands for high-performance turning. Since – as Marcel Leuch says – the demand for larger machines with this technology has increased, decision-makers at Starrag opted to develop a matching MT variant for every STC machine.

Securely-mounted rotary table sets standards

The central new component of the Starrag STC MT variants is the fast- turning rotary table, which replaces the conventional machining table while maintaining the same axis arrangement. This means that for models STC 1000 to STC 1600, the linear X-axis and the rotary B-axis are located in the workpiece. The Y- and Z-axes and swivel axis A are located in the tool. Being of a good size, the workpiece interference diameter is ideal for machining large, cubic parts such as casings. The rotary table used in models STC 1000 MT to STC 1600 MT is designed and built at the Mönchengladbach site. They have also been used for a long time in turning lathes from Berthiez, also a part of the Starrag Group. “Our STC MT machines, or their users, are now also benefiting from this experience,” says Marcel Leuch happily. Our rotary tables are built so well that they are able to main- tain a comparatively high speed even under significant load. The STC 1000 MT can be loaded with up to 3 tons and rotate the component at up to 500 rpm. Even the STC 1600 MT with its load capacity of 8 tons can turn at 320 rpm.

The crucial advantage of the selfconstructed rotary tables is in the rigid bearing. While alternative rotary tables use an internal bearing and external motors for cost reasons, the Starrag Group uses a large external bearing that provides significantly higher resistance to tilt and radial rigidity. The rotary tables can run at high speeds even when heavily loaded, and are not short of torque: an STC 1250 MT, for example, provides 6,000 Nm.

Turning as if on a dedicated machine

Even when it comes to control, there is nothing left to be desired: Multi-task tools with several blades can be used, and eccentric turning is no problem either. “We have already produced several eccentric and conical polygons,” confirms Marcel Leuch. To guarantee high machining quality, it’s not just the tool that is clamped to the spindle while turning. On models STC 1000 MT to STC 1600 MT it is also possible to clamp the rotary table guide. This reduces the effect of an imbalance in the workpiece, which would create small oscillations in the X-axis.

Marcel Leuch supports the theory with results of a test: “We put a sample casing blank with a diameter of 1,800 mm on an STC 1250 MT. In a test cut, we were able to achieve cutting depths of 8 mm with 7/10 mm pitch.” This shows that top-quality turning is possible. The user can confidently dispense with clamping the component for further machining on a separate turning lathe.