Post Processors


When making gcode for your LongMill, or any CNC for that matter, there will come a time where you’ll click the final button to “Generate Gcode”. When this time comes, how will you know that the gcode file is going to be properly suited to your machine? Though many CNCs are able to interpret what’s broadly known as ‘gcode’, the reality is that different manufacturers will have their own quirks that their machines expect to see – you can think of this as gcode 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 any gcode generating program can follow to add small tweaks to the main gcode to ensure it’ll work for your particular CNC machine. If the post-processor isn’t set up correctly or the appropriate one isn’t selected this will usually result in errors, stalls, or unexpected behaviour while running your jobs. Sometimes, even the correct post-processor can cause issues depending on the interface program you’re using (for example, UGS tends to be particularly picky with the gcode that you send it).

To help out, we’ve put together a simple table which shows popular CAM programs alongside the names of 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+UGS GRBL
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)

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

  • Set G28 Safe Retracts as “Clearance Height”
  • Set Output M6 as “No”
  • Set Output Tool Number as “No”

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.