gcoco — G-code Combiner

Combines and nests multiple G-code files into a single output file, automatically arranging pieces within your machine's working area to minimise material waste. Useful when your CAM software (Fusion 360, FreeCAD, etc.) generates one file per part and you want to cut them all in one job.

Designed for Grbl and LinuxCNC machines. Handles standard G-code from common CAM tools.

How it works

Each input file is assumed to have its own origin at (0, 0, 0). gcoco:

1. Parses each file to compute its XY bounding box
2. Arranges all pieces within the specified working area using bin-packing (largest pieces first, minimising wasted space)
3. If pieces don't all fit, splits them across multiple output files
4. Writes combined output files with all coordinates translated to their assigned positions

Between pieces the tool lifts to a safe Z height, rapids to the next piece's position, then continues.

Installation

go install github.com/ashep/gcoco@latest

Or build from source:

git clone https://github.com/ashep/gcoco
cd gcoco
go build -o gcoco .

Usage

gcoco [flags] file1.gcode file2.gcode ...

Flags

Flag	Default	Description
--width	required	Working area width in mm
--height	required	Working area height in mm
--safe-z	5	Z height for rapid moves between pieces (mm)
--spacing	1	Minimum gap between pieces (mm)
--output-dir	.	Directory for output files

Example

gcoco --width 400 --height 300 --safe-z 5 --spacing 3 --output-dir ./out *.nc

Output:

Packing 4 piece(s) into 1 batch(es)...
  Batch 1: 4 piece(s)
    Front.nc  -> X=0.00  Y=0.00
    Back.nc   -> X=0.00  Y=76.80
    Left.nc   -> X=141.00 Y=0.00
    Right.nc  -> X=141.00 Y=76.80
Done. Output written to ./out/

Output files are named combined_1.gcode, combined_2.gcode, etc. — one per batch.

Output file format

Each combined file:

• Sets absolute mode (G90) and mm units (G21)
• Lifts to safe Z before the first piece and between pieces
• Returns to origin (G0 X0 Y0) and ends with M2 at the end

The following codes are stripped from input files and handled at the combined file level: G21, G90, G91, G28, M2, M30.

Limitations

Pieces are not rotated — they are placed in the same orientation as in the input files. If rotating a piece would allow for a better fit, you need to do that in your CAM software before running gcoco.

Requirements

• Input files must use mm units (G21)
• Input files must use absolute coordinates (G90) — the tool assumes this by default, matching standard CAM output
• Compatible with Grbl and LinuxCNC flavoured G-code