I have a creation station running the realtime LinuxCNC OS.
I use it to make PCB, =.
Step one design your circuit in Fritzing.
Step two export as a Gerber file.
Step three open up in pcb2gcodeGUI(python version)
Step four set-up parameters for milling .05 mm for Z work.
Step five open in LinxCNC , set cnc up to carve PCB.
Done.
I tried this and had issues getting the board level enough that the bit cut all the way through the copper, without cutting so deeply it tore up fine traces, but I was using v-shaped engraving bits. What do you use as a cutter?
I would say try using a square endmill. Or maybe round end mill.
It’s hard to find endmills that fine for the sort of layouts I do, alas.
v-bits tend to lift the edges, try these http://www.amazon.com/SPTA-cutters-engraving-router-Proxxon/dp/B01AGH45RU
they break easily but thats why they come in packs of 10 
The trick is the combination of Z-work depth( depth needs to go just enough to cut just the thickness of the copper cladding .035mm), the rate of feed 400 nm/min, and rpm 26500. I am using a 1/8" shaft 60 degree V bit( yes those 10 packs http://www.amazon.com/CNC-Cutting-Carving-Engraving-Cutters/dp/B0126DMZXI/ref=sr_1_6?s=hi&ie=UTF8&qid=1458387108&sr=1-6&keywords=carving+bit+60+degrees+1%2F8 ). Just remember not to cut too deep I set mine to - 0.05 plunge depth in the g-code and so far this has given me the best results.