I really have not understood the point of running these machines on low powered microprocessors when you still need a computer as a user interface and you give up so much functionality. If the size of the electronics is an issue, LinuxCNC runs great on Intel ITX boards. Same with the cost. I run LinuxCNC on a 10 year old computer I got for free. There are plenty of uses for Arduinos (I have several) but this is not one of them.