Please enjoy the GantryPlasmaMachine information. I think there is a lot of reasonably good example code there. Took us a while, but I think we made a nice little plasma / router machine using linuxcnc.
Any questions, contact me at the feedback from on my website: www.tubeclock.com (sorry for the round-a-bout contact method, but it holds the spam-bots a bay a little ;-).
Cheers,
-Peter