Chapter 21 Introduction to CNC Machining 399 Copyright Goodheart-Willcox Co., Inc. • Keep all cooling fans, intakes, and exhausts in the computer control panel clean and free of obstruc- tions. This helps prevent overheating and malfunc- tion of equipment and possibly even equipment fires. • If the machine crashes or does anything out of the ordinary, stop the machine, follow OSHA’s lockout/ tagout procedures, and contact the area supervisor. Lockout/tagout procedures ensure the equipment is stopped and its energy source is removed to prevent accidental injuries. 21.6 CNC Coordinate Systems The CNC program drives the motors that position all of the moving axes. The program uses a coordinate system to com- municate the direction and distance the workpiece or tool must move to the motors and the control. The most common systems in use today are the Cartesian coordinate system and the polar coordinate system. 21.6.1 Cartesian Coordinate System The Cartesian coordinate system, shown in Figure 21-17, forms the basis of CNC programming. Programs, written in either inch or metric units, specify the destination of a particular movement. With the destination established, the axis of movement (X, Y, or Z) and the direction of movement (+ or –) can be identified. To determine whether the move- ment is positive (+) or negative (–), the program is written as though the tool, rather than the work, is doing the moving. Spindle motion is assigned the Z axis. This means that for a drill press or vertical milling machine, the Z axis is vertical. For machines such as a lathe or horizontal milling machine, however, the Z axis is horizontal. See Figure 21-18. The system of coordinates used for machine axis designa- tion is specified according to the right-hand rule of Carte- sian coordinates, as shown in Figure 21-19. Machining instructions can be programmed directly into computer memory by entering the information through the keypad on the control. Programs can also be created and +Z –Z – Y +Y +X –X Goodheart-Willcox Publisher Figure 21-17. The Cartesian coordinate system is the basis of all CNC programming. Each of the three major axes (X, Y, and Z) is perpendicular (at a 90° angle) to the other two. The arrows indicate the direction of travel, positive or negative. WORKPLACE SKILLS Decision Making and Problem Solving Employers value workers who have the ability to make sound decisions and solve problems that arise. The processes for making decisions and solving problems are similar: 1. Identify the problem or issue to be decided. 2. Brainstorm possible solutions. 3. Decide which solution to implement. 4. Implement the solution. 5. Evaluate the results. Having the ability to solve problems on the job shows an employer that you are able to handle more responsibility. Solving problems as a group can strengthen the team and help employees feel more pride in their work. Making decisions and solving problems both require critical thinking skills. These are higher-level skills that enable you to think beyond the obvious. You learn to interpret information and make judgments. Super- visors appreciate employees who can analyze problems and think of workable solutions.