Originally Posted by
dharmic
Don't need a heated bed for some plastics (notably PLA) but others (ABS, Nylon, PET etc) need a warm baseplate or they won't stick down.
The big difference is that you want your printer to run FAST. For example I'm running 120mm/s (around 300ipm) on my printer and max 2000mm/min (80ipm) on my router. On a dedicated printer with lightweight frame and carriage etc it's pretty easy to get that speed, on a CNC designed to throw around a spindle with a bit of force it gets harder.
Worth having a dig if you have the hardware, I believe things like the Rostock Max and the Kossel from which it was born are open source and have plans available for building 'em up.