What are you planning to use this for? Most drills are a bit slow for machining, but if you're using it for drilling only, that might work to some degree. A Dremel tool makes a poor substitute for a CNC spindle, but I suppose you could try it and fry it (turn it on when you start and off when you're done). The basic problem you'll discover is lack of rigidity. Printers don't need much, since they don't have cutting forces to deal with. But CNC routers are more demanding in this respect. Since you're fixing this machine with a new control, why not make it a better printer instead of a crappy router?