CNC machining centers are very popular in manufacturing companies. Just about every company that performs metal-cutting operations has at least one. Since they are so popular, people beginning their CNC careers are often exposed to machining centers first. This makes learning about them an excellent first choice for people beginning their careers in CNC.

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This self-study manual is for people who want to learn G-code level, manual programming for CNC machining centers. It is the companion manual to the Machining Center Setup and Operation self-study manual. We assume in this text that you understand certain things about basic machining practices – topics that are addressed in the Machining Center Setup and Operation manual. This text can also be used by people that have some shop experience who are not interested in learning about how machining centers are set up or how production runs are completed.

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Note that we do offer another self-study manual that covers all three tasks a person must master in order to be fully proficient with CNC machining centers: Machining Center Programming, Setup, and Operation. This more comprehensive manual also assumes you have some shop experience. If you are just getting started with CNC, we recommend that you begin with the Machining Center Setup and Operation self-study manual.

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We use a Key Concepts approach to teaching you about CNC. This proven tutorial method allows us to stress the reasons why things are done as importantly as how they’re done. It provides a building blocks approach to learning. And it limits the number of things you must master in order to become proficient. You must understand six Key Concepts to master CNC machining center G code level, manual programming.

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The six Key Concepts are further divided into sixteen lessons. Most lessons include quizzes and practice exercises right in the text (answers provided close by) and every lesson ends with a test (answers provided at the end of the text). Many lessons also include a programming activity (again, answers provided at the end of the text). This combination of tutorial text, explanatory illustrations, and lots of practice truly turns this text a self-study course that will teach you what you need to know in order to become a proficient CNC machining center programmer.

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Here are the Key Concepts and lessons:

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• Key Concept 1: Know your machine from a programmer's viewpoint 

  • 1: Machine configurations 

  • 2: Visualizing program execution 

  • 3: Program zero and the rectangular coordinate system 

  • 4: Introduction to programming words

• Key Concept 2: You must prepare to write programs 

  • 5: Preparation steps for programming

• Key Concept 3: Understand the motion types 

  • 6: Programming the three most basic motion types

• Key Concept 4: Know the compensation types 

  • 7: Introduction to compensation 

  • 8: Tool length compensation 

  • 9: Cutter radius compensation 

  • 0: Fixture offsets

• Key Concept 5: You must provide structure to your CNC programs 

  • 11: Introduction to program structure 

  • 12: Four types of program format

• Key Concept 6: Special features that help with programming 

  • 13: Hole-machining canned cycles 

  • 14: Working with subprograms

  • 15: Other special programming features 

  • 16: Programming rotary devices

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When you finish reading this text and doing the exercises, you will have a firm understanding of what it takes to program a CNC machining center at G code level.

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A note about G code level programming

It is at G code level that a CNC programmer can be the most intimate with the machine. Commands in the program explicitly tell the machine what to do, one function at a time. G code level programmers (also called manual programmers) develop these commands in exactly the same manner that the CNC machine will interpret them.

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There is another way to create CNC programs – by using a computer aided manufacturing (CAM) system. With a CAM system, a programmer works at a higher level, importing a drawing form a computer aided design (CAD) system and then specifying how the workpiece is to be machined. The CAM system will automatically create the G code level program (the same kind of program a G code level programmer creates manually).

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While CAM systems take much of the tediousness out of creating CNC programs – and there are some people in the industry that feel that there is no need to learn about G code – we feel a firm understanding of G code level programming is an important prerequisite to learning how to use a cam system. Without a knowledge of G code, you will not be able to determine if the CAM system is generating appropriate (correct) commands for your CNC machine. And if programs must be modified at the machine, changes must be made at G code level.

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We compare learning G code prior to learning a CAM system to learning how to perform longhand arithmetic calculations before learning how to use a calculator. A person will not be able to judge whether a calculator’s answer is correct if they don’t know longhand arithmetic. In similar fashion, a CAM system programmer will not be able to judge the CAM system’s output (G code) if they don’t understand G code level programming.