A novel approach to 5 axis NC milling simulation using GPU is presented. Modelling swept volumes of a milling tool that undergoes a translational and rotational motion is based on the idea behind Gauss maps. The main process is that it 1) transforms the tool shape and the moving direction of the tool from Euclidean space into an unit sphere by means of Gauss function and gets the spherical domains which are called Tool map (T-Map) and Contact map (C-Map) respectively 2) finds an intersection region of T-Map with C-Map and 3) transforms intersected region inversely into Euclidean space to get the envelope profile of the tool at prescribed instant time. As of now, Graphics Processor Unit (GPU) in graphics hardware is being developed more drastically as compared with Central Processing Unit (CPU). To achieve our purpose of updating the work piece GPU is exploited as follows: 1) a swept volume is rendered using graphics hardware (Model building) 2) colour and depth information is read back from the frame buffer in GPU to CPU (sampling) 3) at last, the updated work piece is built based on extracted data (surface reconstruction).