If you want to use your RepRap for CNC use, such as milling PCB’s, regular 3D printing firmwares might not be ideal. For instance, Marlin is not able to handle the slow step rates used for CNC work.
I have ported grbl, a firmware specifically for CNC use (from which Marlin derived its acceleration routines), to Printrboard and Teensylu. You can download it from my fork at: https://github.com/lincomatic/grbl.