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gcmc - G-Code Meta Compiler


Gcmc is a front-end language for generating G-code, SVG and DXF for CNC mills, lathes, laser cutters and other numerical controlled machines employing G-code, SVG or DXF. The language is a context-free grammar created to overcome the archaic format of G-code programming and aims to be more readable and understandable. Gcmc makes extensive use of vector mathematics to support the 3D nature of CNC machining.

An introduction document is available. The introduction goes through basic syntax and program outline and describes an example to create involute gears in under 200 lines of code (under 100 lines when excluding source code comments).

Getting and building gcmc

You can get the source from the link below. The windows executable is a 32bit MinGW cross-compiled command-line version.
Source tarball: gcmc-1.8.2.tar.gz
Windows exe:
Git repo:
Please note: the git repository has been moved from to You should rebase your local repository if you have cloned it.

Older sources are available and a SHA1 sum and/or SHA256 sum may be used to verify the archives.

Building from source is straight forward and should function on Linux, *BSD, MinGW/MSYS and Cygwin:
$ tar xzf gcmc-1.8.2.tar.gz
$ cd gcmc-1.8.2
$ ./configure
$ make

After 'make' you should have an executable in the 'src' directory named 'gcmc'. For a MinGW cross-compile you should use 'configure --host i686-w64-mingw32' or whatever your cross-target-host specifier is and it should result in 'gcmc.exe'.

Building on any system with a different set of autotools may require you to re-configure the setup. Gcmc 1.8.2 uses autotools 1.15, whereas Debian 7 is on version 1.10 and Debian 8 is on version 1.14. Other distributions may have different versions installed. Please read the first part of doc/ on how to re-configure. This should work across distributions.

Running gcmc

Running gcmc, assuming you are in the src directory, is as simple as:
$ ./gcmc -o output.ngc input.gcmc

This will convert the input file "input.gcmc" into a G-code file "output.ngc". The output is written to stdout if no -o option is given. Stdin is used if no input file is given.

You may compile and inspect the examples by running (from the top or the example directory):
$ make examples

This will give you G-code, SVG and DXF versions of the examples, which can be inspected with the appropriate programs.

The gcmc man-page gives you a complete summary of all option.


gcmc-1.8.2 - 2017-02-19
  • Fix: spindle() function must first set speed with S before enabling spindle with M3/M4
gcmc-1.8.1 - 2017-02-11
  • Fix: Use-after-free bug in filename referencing when handling includes
  • Fix: Split the Bezier min-length and co-linear calculations to become slightly more accurate
gcmc-1.8.0 - 2016-07-25
  • Feature: Convert all internal string handling to Unicode (wchar_t)
  • Feature: to_float() and to_int() now can convert strings to values including units
  • Feature: Functions insert(), delete(), head(), tail() and reverse() can now operate on strings
  • Feature: Allow strings to be indexed as rvalues, returning the indexed character as string
  • Feature: Add to_val() and to_chr() functions to allow character manipulations
  • Feature: Add relocate() function to support adhoc relative offsets
  • Feature: Add TODO (wish)list
  • Fix: Several interpreter memory leaks plugged using valgrind
  • Fix: Allow delete() to delete all entries
  • Fix: Use correct source argument in insert() to insert into target
  • Fix: Fix relative arcs, specifically SVG, to use the correct movement
  • Fix: Fix arcs and circles, use global position whith undef end coord.
For older changes see Changes page for details.

Bugs reports and feature requests

Please report any bugs you may encounter to gcmc _at_ Please include an example that triggers the bug.

If you want more/extra/different features included, then write me an email with the request and a description what you want to add and want to achieve with the change or addition.

Gcmc documentation

gcmc man-page All command-line options and switches.
gcmc introduction page Starting with a simple step-by-step introduction to the basic concepts and ending with the creation of an example to create involute gears.
gcmc syntax page Detailed description of language syntax and its semantics.
gcmc function reference page All built-in functions described with all parameters, types and operational modes.
gcmc library page Library functions are more complex operations like tool compensation and canned drill sequences.

Gcmc examples and screenshots

(click on images to enlarge)

Text fonts (source: text-fonts.gcmc)

Text on a circle path (source: text-on-circle.gcmc)

Involute gears (sources: involute-gear.gcmc and

Cycloids (source: cycloids.gcmc)

Ball-in-a-Cube (source: ball-in-cube.gcmc)

Continuous curvature pocketing (sources: cc_hole.gcmc and

Sunflower floret arrangement of 500 holes (source: floret-vogel.gcmc)
Rapid path is about 55.5 meters without sorting the individual holes:

Sorting the holes with a simple nearest neighbor algorithm shortens the rapid path to about 4.1 meters:

Using a bin-sorting algorithm shortens the rapid path to about 3.7 meters using 20 bins:

Tool-size compensation of an open or closed path on either left or right side (source: tool-compensate.gcmc)

High-speed milling using trochoidal movement (source: trochoidal.gcmc)

Executive Decision Maker Pro box example (source)
edm-pro-ngc edm-pro-svg
Cutter example (source)
cutter-ngc cutter-svg
Wheels example (source)
wheels-ngc wheels-svg

Posted: 2013-11-04
Updated: 2015-05-14

Overengineering @ request