That looks like the head of a Foredom flexshaft. But since these are only used as spindles on cheap Chinese routers, it's probably a knock-off. The original is a good choice for intermittent hand work, but it wouldn't last long as a CNC spindle (and the original probably uses better bearings). Also, a Jacobs chuck is okay for drilling, but not a good choice for milling, especially with small bits, since the run-out is too great and will break them. If you plan to use this for fine work, or extended periods, replace it with something that uses collets.