Your controller may or may not require a Program Number, but it is a good idea to provide one. A Program Number is an “O” word (in g-code we refer to the letters as “words” because each is a “word” telling the controller something to do). Programs and subprograms need a number for reference, and this is provided by the Program Number. There are still machines out there happily churning out parts that worked this way, but by now their controllers have often been upgraded or at least the tape reader has been replaced with a serial port or USB key front end. They have a historical origin dating back to when nc programs were stored on punched paper tape. All these references to “Leaders” and “Tape” may seem odd to relative newcomers to cnc. Such comments are referred to as being in the “Leader” section. Most will ignore anything after the “%”, so you can put comments there. Put one as the first line (block) and one as the last line (block) of any g-code program.

The percent “%” is used to denote the beginning and end of a program. Let’s look at the function of each of these beginning parts, and remember, a block doesn’t have to have any of them. In particular, it can optionally begin with a Sequence Number, a Block Skip, a Program Number, or a Tape Start/End character (“%”). Certain parts of a block have to come first if they are to be present in the block. Beginning a BlockĪ block can contain a number of optional parts. So the first thing you have to know is how to create blocks since they’re the basic unit of a g-code part program. But, there’s a lot more power waiting to be unleashed if we delve a little deeper into the g-code language. As I’ve been saying, it’s like having a really nice manual machine with DRO’s and Power Feeds on all axes. Up until now, we’ve been typing in one block at a time rather than trying to create full g-code program.

G-Code Basics: Program Format and Structure CNCCookbook’s G-Code Tutorial Blocks = Lines of G-CodeĪ line of g-code is commonly called a “Block”.

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