Post Processors


When making gcode for any CNC machine, there will come a time where you’ll click the final button to “Generate Gcode”. Doing so, how will you know that the g-code file is going to be properly suited to your particular CNC? Though many CNCs are able to interpret what’s broadly known as ‘g-code’, the reality is that different manufacturers have their own quirks that their machines expect to see; you can think of this as g-code being the primary language while different CNCs speak with dialects or accents. For the LongMill and many other hobby CNCs, this dialect is known as “GRBL”.

This is where post-processing comes in. A ‘post-processor’ is simply a set of rules that can be followed to add tweaks to the main g-code and ensure it’ll work for particular machines. If the post-processor isn’t selected or set up correctly this will usually result in errors, stalls, or unexpected behaviour while running your jobs.

To help out, we’ve put together a simple table which shows popular CAM programs and their LongMill-compatible post-processors. Some CAM programs may not have post-processor options since they’re already designed for hobby CNC use:

CAM SoftwarePost-Processor
Vectric Cut2D, Vectric VCarve, Vectric AspireGRBL (in) or GRBL (mm)
Carveco Maker, Carveco Maker+GRBL (in) or GRBL (mm)
Fusion 360GRBL**
Easel, Easel ProNo selection required
Carbide CreateGRBL
CAMLabNo selection required
ESTL CamNo selection required
FreeCADGRBL (in) or GRBL (mm)
Inventor CAMGRBL (in) or GRBL (mm)

**To avoid potential issues with Fusion 360, we also recommend you make the following checks to your post-processor:

  • G28 Safe Retracts set as โ€œClearance Heightโ€
  • Output M6 set as “No”
  • Output Tool Number set as “No”

If you’re interested, there have also been instances of LM community members putting their own post-processors to download. Some examples include:

Fun fact: some other members of the GRBL CNC family include OpenBuilds, Shapeoko, BobsCNC and X-Carve – all starting just as the LongMill has from an Arduino Uno.