Post-processor and G-code output in CNC Programming

Introduction

A post-processor changes toolpath data into G-code that a CNC machine understands. It makes sure the machine runs the job correctly.

When you want to turn a CAD design into instructions for a CNC machine.

When you need to customize G-code for a specific CNC machine model.

When you want to add special commands or safety checks to your CNC program.

When switching between different CNC machines that use different G-code formats.

Syntax

CNC Programming

function postProcess(toolpathData) {
  // Convert toolpath data to G-code commands
  let gcode = '';
  for (const move of toolpathData) {
    gcode += `G1 X${move.x} Y${move.y} Z${move.z}\n`;
  }
  return gcode;
}

This example shows a simple post-processor function in JavaScript.

Each move is converted to a G1 command with X, Y, Z coordinates.

Examples

G0 moves the tool quickly without cutting.G1 moves the tool slowly to cut material.

CNC Programming

G0 X0 Y0 Z5  ; Rapid move to start position
G1 X10 Y10 Z-1 ; Linear cut move

This function creates G1 moves only with X and Y coordinates.

CNC Programming

function simplePostProcessor(moves) {
  let gcode = '';
  for (const m of moves) {
    gcode += `G1 X${m.x} Y${m.y}\n`;
  }
  return gcode;
}

Sample Program

This script converts a list of tool moves into G-code commands. It sets units to millimeters and uses absolute positioning. Each move is a G1 command with feed rate 1000. The program ends with M30.

CNC Programming

function postProcess(toolpathData) {
  let gcode = 'G21 ; Set units to millimeters\n';
  gcode += 'G90 ; Use absolute positioning\n';
  for (const move of toolpathData) {
    gcode += `G1 X${move.x} Y${move.y} Z${move.z} F1000\n`;
  }
  gcode += 'M30 ; End of program\n';
  return gcode;
}

const toolpath = [
  {x: 0, y: 0, z: 5},
  {x: 10, y: 0, z: 0},
  {x: 10, y: 10, z: -1},
  {x: 0, y: 10, z: -1},
  {x: 0, y: 0, z: 5}
];

const gcodeOutput = postProcess(toolpath);
console.log(gcodeOutput);

Important Notes

Different CNC machines may require different G-code formats.

Post-processors help customize output for each machine's needs.

Always test G-code on a simulator before running on a real machine.

Summary

Post-processors turn toolpath data into machine-ready G-code.

They help customize instructions for different CNC machines.

Writing simple post-processors can automate CNC programming tasks.