Abstract: A PC-based open computer numerical control system is described. This system can be used both for virtual axis tool grinders and for conventional tool grinders. The hardware setup and software structure are presented. The machine controller consists of two major elements: a PC and an IN/OUT board (installed inside the PC). The software mainly includes movement function lib and user application, which can be reusable. Movement variables are calculated and the resultant data for the axis movement are temporarily stored in the hard disk. The data are then sent to generate real time signals to drive the motors. Examples are detailed to show the grinding control of twist drill points on both a virtual axis tool grinder and a conventional tool grinder.