A CNC milling machine has slower spindle speed as compared to CNC router. Due to this, the CNC miller is capable of handling harder work pieces than CNC router, however, the CNC router has an advantage when making sharp edges. The high spindle speed in CNC router is obtained generally by higher gear ratio, because of this, the resolution of router decreases. A CNC router is also characterized by larger working space than a milling machine.
CNC Router is for soft jobs like wood, plastic and foam, as it takes very less time in handling those jobs. It is not for industrial grade jobs. A CNC Milling machine is for hard jobs where much time is needed. Milling cutters are used to remove material from the surface of a work piece.
On a typical CNC router, the work is stationary and the spindle-head moves in x/y/z coordinates, But CNC mill, the work moves in x/y coordinates (ie, is attached to an x/y table) and the spindle-head moves in the z axis only.
A CNC miller generally cuts slow RPM, from 3,000 to 5,000 with a lot of torque, whereas a CNC router will usually run 10 times that with 30,000 to 50,000 RPM with much less torque.