The most CNC-machining centres own a common aggregates support for the processing-aggregates like working spindle and boring head, often also for further milling spindles. They lower together during the processing, because there is only one Z-axis for the aggregates support. This causes a strong limitation of the processing height. There are always tools that lower together with the other ones but are not supposed to touch the workpiece. The efficient extraction of single aggregates is limited, too.
The easiest way to solve this problem is the positioning of the aggregates support via Z-axis. The required aggregate is lowered by a defined value. The machine has to be designed for the traversing path of the actual Z-axis plus stroke, which is a disadvantage of this variant. Thereby the actual working range is limited in Z-direction or the cantilever has to be arranged higher than necessary to use the possible traversing range.
Another easy variant with independent z-axes (for example Weeke 2 Z- axes) contains the arrangement of all aggregates on a common aggregates support. However, the working spindles and boring unit here each have an own Z-axis. The aggregates support can be arranged fixedly and the design of the cantilever can be very low in contrast to the pneumatic stroke-variant with the same workpiece height.
Each working unit gets an own aggregates support in another variant, which is quite expensive, but has big advantages especially for high-performance manchines. It is possible to achieve a very efficient extraction, right up to hoods with their own CNC-axes, and the weight distribution for example for high-dynamic processes in 5-axes spindles can be optimized. A free positioning of the aggregates at the cantilever or portal is possible, too. Significantly more independent z-axes may be present in this variant. It is used for example in machines with multiple milling spindles for the simultaneous processing of mulitple identical workpieces.