403 Copyright Goodheart-Willcox Co., Inc. Chapter Review Summary • Computer numerical control (CNC) is a computer- controlled version of the numerical control machines developed in the 1950s. • CNC technology results in faster, more precise machin- ing, but CNC machines typically cost much more than their manual counterparts. • CNC milling machines are similar to traditional milling machines but have built-in CNC capabilities. • Machining centers are CNC milling machines equipped with automatic tool changers. • CNC turning machines consist of computer-controlled lathes, including basic CNC lathes, gang-tool lathes, tur- ret lathes, and Swiss-type turning centers. • All of the safety guidelines for manual machines should be followed for their CNC counterparts. • CNC machines have additional safety guidelines related to the computer and the automation of the equipment. • CNC programs use the Cartesian coordinate system and the polar coordinate system to communicate the direc- tion and distance a workpiece or tool must move. • CNC axes are driven by stepper motors or servomotors, depending on the speed and cost of the equipment. Review Questions Answer the following questions using the information provided in this chapter. 1. What medium was used to store the programs that controlled machine tools in the original numerical control machines? 2. What technological advance in the 1960s was responsible for dramatically increasing the use of numerical control technology? 3. Name two advantages of using CNC equipment instead of manual methods. 4. What is the biggest disadvantage of using CNC? 5. How many axes of movement does a basic milling center have? 6. Basic CNC milling centers use a method called ______ that allows operators to select operations from menus without having to know a programming language. 7. Why might a milling center need more axes of rotation than are provided on a basic model? 8. Describe the difference between a basic CNC lathe and a gang-tool lathe. 9. Why might you avoid using a gang-tool lathe for parts that have a relatively large diameter? 10. What is the purpose of the turret on a turret lathe? 11. Why do operators of turret lathes require more training than those who operate basic CNC lathes? 12. Which type of CNC turning center would be used to machine small parts that have a high degree of elaborate detail? 13. When changing tools manually, wait for the machine axes and the ______ to come to a complete stop. 14. What is the purpose of a dry cycle? 15. In the ______ coordinate system, movement is specified in a positive or negative direction along the X, Y, or Z axis. 16. The ______ coordinate system specifies movement by giving a straight-line distance and travel angle from a tool’s current point location. 17. A(n) ______ is a transducer that provides electronic feedback about the position of the moving axes to the control in a CNC machine. 18. What is the difference between an open-loop system and a closed-loop system? 19. Why must the lead screws and lead nuts in the motors that drive the CNC machine axes be checked and replaced at regular intervals?