Machining Fundamentals 398 Copyright Goodheart-Willcox Co., Inc. 21.5 CNC Safety The only difference between CNC machines and their manu- ally operated counterparts is that the CNC machines are automated. They are controlled by a computer system as it executes a computer program written by a human. There- fore, the safety warnings and cautions related to manual machines are applicable to CNC equipment as well. Review Chapter 3, Shop Safety, for more information. The following are additional safety concerns related solely to CNC equipment: • Before operating a machine for the first time, obtain training on the machine. You must have a working knowledge of the machine and safe operating prac- tices. Different machines may have different operat- ing mechanisms. Read the operation and maintenance manuals provided with each machine. • Do not remove or bypass guards, doors, and other safety devices on any CNC machine so that they do not work as they were designed. • Know the sequence of operations executed by any program run by the machine you are operating. This allows you to recognize problems with the machine when it does something out of the ordinary. • When changing tools manually, wait for the machine axes and the spindle to come to a complete stop. • Know where the emergency stop buttons are located. One will always be located on the control panel and others may be located in other areas around the CNC Software, Inc. ©Copyright 1983–2013. All rights reserved. Figure 21-15. A small, intricate component made of brass being machined on a Swiss-type turning center with a gang-tool setup. machine. The emergency stop brings the program to an immediate halt. • Know how to manually jog the machine to a point clear of the workpiece. • Know how to restart the program from its beginning and, if multiple tools are part of the program, how to manually change the tools. This will have to be done in the event of an emergency stop. • Be familiar with all error codes and cautions that may appear on the control screen. Know what steps to take to correct each error code. • Obtain training in the use of all auxiliary devices on the machine. Many machines have coolant systems, automated lubrication systems for spindles and other moving parts, and automated chip handlers. Know how to maintain these. • Never try to remove chips while the machine is run- ning, even if the chips appear to be clear of the work area. • Cycle all programs once without a part in place dur- ing setup (this is called a dry cycle). It is best to run the program in single-step mode, with the feed rate overridden to its lowest range. This can prevent an accidental machine crash. • CNC programs can also be verified by machining a sample part from plastic, wax, or a similar inexpen- sive material, Figure 21-16. • Be careful around automated tool changers. They can move without warning and trap an operator against a part of the machine. Automated tool changers are usually pneumatically powered, so take care around compressed air systems as well. CNC Software, Inc. ©Copyright 1983–2013. All rights reserved. Figure 21-16. CNC programs can be verifi ed by producing a part in an inexpensive material, such as plastic or wax.