Wow, just wanted to say thanks for this (EVEN ALL THESE YEARS LATER!!!), I am completely new to CNC and just recently got a good size OX CNC Router.
It runs grbl, not mach but I stumbled across this post/site when looking for a good picture resource to engrave and carve from etc.... I have barely scratched the surface of what's available, but for someone like myself who has loads of cheap bits, it's fantastic being able to get ready planned out pics that translate to great shallow carve/engrave files and there's Hundreds of them!