GCMC Guilloche Plot Generator

It turns out the Spirograph patterns I’d been using to wring out the MPCNC are also known as Guilloché, perhaps after the guy who invented a lathe-turning machine to engrave them. Sounds pretentious, but they still look nice:

Guilloche 591991062 - scanned

Guilloche 591991062 – scanned

With the ballpoint pen / knife collet holder in mind, I stripped the tool changes out of the Spirograph generator GCMC source code, set the “paper size” to a convenient 100 mm square, and tidied up the code a bit.

As with Spirograph patterns, changing the random number seed produces entirely different results. A collection differing in the last digit, previewed online:

Seed = 213478836:

Guilloche 213478836

Guilloche 213478836

Seed = 213478837:

Guilloche 213478837

Guilloche 213478837

Seed = 213478838:

Guilloche 213478838

Guilloche 213478838

Seed = 213478839:

Guilloche 213478839

Guilloche 213478839

They’re such unique snowflakes …

The Bash script now accepts a single parameter to force the PRNG seed to a value you presumably want to plot again, rather than just accept whatever the Gods of Cosmic Jest will pick for you.

The GCMC source code and Bash (or whatever) script feeding it as a GitHub Gist:


  1. MPCNC: Acrylic Engraving First Light | The Smell of Molten Projects in the Morning
  2. MPCNC: Guilloche Engraving First Light | The Smell of Molten Projects in the Morning

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