Abstract: Methods of interference checking in NC programming are briefly discussed. A new approach for interference detection in 3-axis NC machining of sculptured surfaces based on the concept of construction space is introduced. The space is first divided into millable space and gouge one, and then the toolpath segments in the gouge space are checked and eliminated. To detect cutter interference, the cutter-location-surface and safeguard-surface of the part are discretized and triangulated. Then, the gouge free toolpath is generated based on the uppermost envelope of these triangles. The algorithm described is stable and reliable, and is suitable for ball-end, fillet-end and flat-end cutters.