Chapter 21 Introduction to CNC Machining 395 Copyright Goodheart-Willcox Co., Inc. machined in a single CNC program cycle within the cubic space provided by a basic 3-axis system, Figure 21-8. The additional axes allow for more flexibility in the types and complexity of parts that can be produced. The advantages of the VMC are tied to its machining capabilities. VMC machines vary in accuracy, precision, speed, power, tool change capabilities, and the ability to add rotational axes. Their biggest disadvantage is cost. As capa- bilities increase, so do the costs of the machines. Costs can be controlled by selecting equipment with fewer options, then tailoring the machine setups in-house to meet the requirements. However, such practices limit the flexibility of the machines. 21.4 CNC Turning Machines CNC turning machines are designed to machine cylindrical parts about an axis of rotation. A CNC turning machine is basically a computer-controlled lathe, and it has the same fea- tures as a manual lathe. A CNC turning machine equipped with an automatic tool changer is known as a turning center, Figure 21-9. There are many types of CNC turning machines, each with its own advantages and disadvantages. The four types of CNC turning machines described in this chapter are presented in order from least expensive to most expensive because one of the first things a company studies when con- sidering the purchase of CNC equipment is the cost of the machinery. 21.4.1 Basic CNC Lathes Basic CNC lathes are common lathes with CNC capabilities included, Figure 21-10. Some CNC lathes can be operated in manual mode, just like a traditional engine lathe, as well as in full CNC mode. The control system built into this machine uses the same type of programming used in more expensive models. Its computer capabilities differ only in the amount of storage memory available. As memory capacity increases, so does the cost of the machine. Z B W X Y C Y X C A Z A B Goodheart-Willcox Publisher Figure 21-8. Multiaxis machining. A—A 5-axis CNC milling machine. B—A 6-axis vertical machining center (VMC). A B Mazak MAG IAS, LLC Figure 21-9. Turning centers. A—This 4-axis turning center permits operations to be performed on both sides of the workpiece, reducing machining time. B—Another example of a 4-axis vertical turning center.