Post processors
The post processor writes your toolpaths as G-code in the exact dialect your controller expects. Pick the one that matches your controller, not your machine brand. Symptoms of the wrong post look like machine faults but are not.
What it does
CAM knows the geometry: where the tool goes, how fast, how deep. The post processor knows your machine: what commands it accepts, how it wants a tool change expressed, whether it supports arcs, what it needs at the start and end of a file, and which units.
Same toolpaths, different post, completely different text file.
Symptoms of the wrong post
| What happens | Usual post cause |
|---|---|
| Everything is 25.4 times too big or too small | Post outputs the wrong units for the controller |
| The machine ignores tool changes and keeps cutting | Tool change command the controller does not understand |
| The spindle does not start, or does not stop | Spindle commands in a form the controller does not accept |
| The tool plunges at rapid speed | Plunge expressed as a rapid rather than a feed move |
| Circles come out faceted | Arc fitting off, so arcs are output as line segments |
| The controller throws an error on a specific line | A command the controller does not support |
| The file does not load at all | Wrong file extension or format for the controller |
All of these look like machine problems. They are not. If a machine behaved normally and then started doing one of these after a software change, check the post first.
Choosing the right one
The order to look:
- Your machine manufacturer's own documentation or downloads.
- The CAM package's bundled post list, which usually covers common controllers.
- Your machine's user community, which often maintains a refined version.
Testing a new post safely
- Post a small, simple job.
- Open the file in a text editor and read the first twenty lines. Check the units command, the spindle command and the coordinate system.
- Load it and run it in the air, well above the material, watching what the machine does.
- Then run it in scrap.
- Only then use it on real material.
When to edit a post
Rarely, and only with a specific reason: adding a pause at tool changes, changing the spindle warm-up delay, adjusting how the file ends. Post files are plain text and editable, and a broken post produces G-code that can drive your machine into something. Keep a copy of the original before you change anything.