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Building Block 4 of 5

G-Code Programming

Writing M and G code for mill and lathe, then visualizing what it does. Students program in the NextGen CNC Simulator, so practice is not rationed by how many lab machines are free.

  • An end mill cutting a circular boss on a steel block held in a Kurt vise on a CNC mill, with chips scattered across the vise and parallels.

    CNC mill project

    The program from the previous screen, cutting metal

  • A turning insert cutting a stepped shaft on a CNC lathe, the workpiece spinning in the chuck with the finished diameters visible behind the tool.

    CNC lathe project

    Turning the profile down to the finished diameters

Why this comes before CAM

CAM is only as good as the person driving it. Machinists, and people with machining backgrounds, are the ones who make successful CAM programmers — and writing G-code by hand is a large part of what builds that.

That is why this is a prerequisite rather than a formality. A student who has written the code can read what a post processor gives them and tell whether it is sane.

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What this building block covers

  • 3-axis CNC milling machine programming
  • CNC lathe programming
  • Programming workbook, built for certification preparation
  • CNC mill projects — print reading through to part inspection
  • CNC lathe projects — print reading through to part inspection
  • Multi-axis machining
A student has hovered G41 in the code panel of the NextGen simulator. A panel explains it as Cutter Comp Left, climb cut, modal group 7, and warns that it requires a D word, that the controller setting decides whether the offset is a radius or a diameter, that it cannot be switched on or off during an arc, and that it must be activated at least half a diameter away from the part.
Hover a code, and the editor explains it — including the traps.

The reference is in the editor

Every code carries its own explanation: what it does, which modal group it belongs to, and the things that catch people out. G41 needs a D word. It cannot be turned on or off inside an arc. It wants at least half a tool diameter of lead-in before it reaches the part.

A student meets that at the moment they need it, rather than in a table they have to know to go looking for — and an instructor stops answering the same question about cutter compensation every term.

Optional: Haas Intuitive Programming

Conversational programming for mill and lathe on Haas controls, available alongside the core path for programs running Haas machines.

Projects, not exercises

The project courses run the whole job rather than a fragment of it: read the print, write the program, choose tooling and work holding, set the machine, run it, and inspect what comes off. That is the sequence a shop actually pays for, and it is where the earlier building blocks come together.

A G13 circular pocket canned cycle in the NextGen simulator. The code panel shows the cycle called with a three-quarter inch end mill, switching to incremental mode for a 3.5 inch diameter pocket, and the simulation view draws the resulting spiral toolpath stepping outward from the centre.
A canned cycle written, then run — the spiral stepping out from centre is the machine’s interpretation of two lines of code.

The NextGen CNC Simulator carries the programming practice, so a mistake costs seconds rather than a scrapped billet.

Next in the pathway

G-Code Programming leads into CAM Programming, where students move from writing code by hand to driving it from a model.

Building Block 5: CAM Programming