• Identify the program’s list instructions.
• Understand the Program Format
• Understand the G & M Codes.

CNC Program Language and Structure

CNC programs list instructions to be performed in the order they are written. They read like a book, left to right and top-down. Each sentence in a CNC program is written on a separate line, called a Block. Blocks are arranged in a specific sequence that promotes safety, predictability and readability, so it is important to follow a standard program structure.  In this course, a basic CNC program is separated into three sections: the header, the body, and the footer.

The blocks (lines of code) are arranged in the following order:

The Header:

The steps listed above represent the simplest type of CNC program, where only one tool is used and one operation performed. Programs that use multiple tools repeat steps two through nine for each.

Table 1 and Table 2 below show the most common G and M codes that should be memorized if possible. CNC codes also use letters. Table 3 offers definitions for different letters.

Like any language, the G-code language has rules. For example, some codes are modal, meaning they do not have to be repeated if they do not change between blocks. Some codes have different meanings depending on how and where there are used.

While these rules are covered in this chapter, do not concern yourself with learning every nuance of the language. It is the job of the CNC Programmer to properly format and write the CNC program.  A CNC Operator follows the program.  It is good for an operator to understand the format of the program.