Anatomy of a CNC Router
The spindle is the shaft that rotates very fast. It is attached to a big motor on one side and your cutting bit (or a holder that holds your bit) on the other side. For CNC routers, a spindle speed of 10,000-20,000 RPM is standard. For CNC mills, the spindle is generally much slower at 1,000-10,000 RPM, but with significantly more torque.