The prerequisite for four-axis turning, also known as balance cutting, is a turning machine with at least two independent tool carriers. As a rule, this involves one tool turret behind the rotation center and a second in front of the rotation center. The machine has to be designed in such a way that both tool carriers can be engaged on one workpiece simultaneously - one on the main spindle and one on the counter spindle. If both tool carriers are moved independently, two independent CNC programs are executed simultaneously, thus activating a multi-channel structure in the CNC control system.
In this respect, four-axis chip removal can be considered a special form of multi-channel machining: simultaneous machining with two identical tools (for example two 80-degree roughing inserts) on one machining profile of the workpiece. Balance cutting offers two significant advantages compared with machining using only one cutting insert: First, when machining long, thin components, the balancing of the cutting forces increases the dimensional accuracy, since the use of two opposite cutting inserts eliminates the distortion of the workpiece resulting from the cutting force. Second, the cutting volume per time is increased. There are two possible strategies for achieving these benefits: either synchronous or offset tool path control.